Ticket #21280817 - Windows console rewrite to only create one thread per stdio channel.

Functional, but not complete.

1 files changed, 1294 insertions, 667 deletions

diff --git a/win/tclWinConsole.c b/win/tclWinConsole.c
index c3ba814..14cc6e5 100644
--- a/win/tclWinConsole.c
+++ b/win/tclWinConsole.c
@@ -2,15 +2,51 @@
  * tclWinConsole.c --
  *
  *	This file implements the Windows-specific console functions, and the
- *	"console" channel driver.
+ *	"console" channel driver. Windows 7 or later required.
  *
- * Copyright © 1999 Scriptics Corp.
+ * Copyright © 2022 Ashok P. Nadkarni
  *
  * See the file "license.terms" for information on usage and redistribution of
  * this file, and for a DISCLAIMER OF ALL WARRANTIES.
  */
 
+#define TCL_CONSOLE_DEBUG
+#ifdef TCL_CONSOLE_DEBUG
+#undef NDEBUG /* Enable asserts */
+#endif
+
 #include "tclWinInt.h"
+#include <assert.h>
+#include <ctype.h>
+
+/*
+ * A general note on the design: The console channel driver differs from most
+ * other drivers in the following respects:
+ *
+ * - There can be at most 3 console handles at any time since Windows does
+ *   support allocation of more than one console (with three handles
+ *   corresponding to stdin, stdout, stderr)
+ *
+ * - Consoles are created / inherited at process startup. There is currently
+ *   no way in Tcl to programmatically create a console. Even if there were
+ *   added the above Windows limitation would still apply.
+ *
+ * - Unlike files, sockets etc. where there is a one-to-one
+ *   correspondence between Tcl channels and operating system handles,
+ *   std* channels are shared amongst threads which means there can be
+ *   multiple Tcl channels corresponding to a single console handle.
+ *
+ * - Even with multiple threads, more than one file event handler is unlikely.
+ *   It does not make sense for multiple threads to register handlers for
+ *   stdin because the input would be randomly fragmented amongst the threads
+ *   (not even on a per line basis).
+ *
+ * Various design factors are driven by the above, e.g. use of lists instead
+ * of hash tables (at most 3 console handles) and use of global instead of
+ * per thread queues which simplifies lock management particularly because
+ * thread-console relation is not one-one and is likely more performant as
+ * well with fewer locks needing to be obtained.
+ */
 
 /*
  * The following variable is used to tell whether this module has been
@@ -19,106 +55,119 @@
 
 static int initialized = 0;
 
-/*
- * The consoleMutex locks around access to the initialized variable, and it is
- * used to protect background threads from being terminated while they are
- * using APIs that hold locks.
- */
-
-TCL_DECLARE_MUTEX(consoleMutex)
+#define CONSOLE_BUFFER_SIZE 8000 // TODO - must be at least 2 :-)
 
 /*
- * Bit masks used in the flags field of the ConsoleInfo structure below.
+ * Ring buffer for storing data. Actual data is from bufPtr[start]:bufPtr[size-1]
+ * and bufPtr[0]:bufPtr[length - (size-start)].
  */
-
-#define CONSOLE_PENDING	 (1<<0)	/* Message is pending in the queue. */
-#define CONSOLE_ASYNC	 (1<<1)	/* Channel is non-blocking. */
-#define CONSOLE_READ_OPS (1<<4)	/* Channel supports read-related ops. */
-#define CONSOLE_RESET    (1<<5)	/* Console mode needs to be reset. */
+#if TCL_MAJOR_VERSION > 8
+typedef ptrdiff_t RingSizeT; /* Tcl9 TODO */
+#define RingSizeT_MAX PTRDIFF_MAX
+#else
+typedef int RingSizeT;
+#define RingSizeT_MAX INT_MAX
+#endif
+typedef struct RingBuffer {
+    char *bufPtr;	/* Pointer to buffer storage */
+    RingSizeT capacity;	/* Size of the buffer in RingBufferChar */
+    RingSizeT start;	/* Start of the data within the buffer. */
+    RingSizeT length;	/* Number of RingBufferChar*/
+} RingBuffer;
+#define RingBufferLength(ringPtr_) ((ringPtr_)->length)
+#define RingBufferFreeSpace(ringPtr_) ((ringPtr_)->capacity - (ringPtr_)->length)
+#define RINGBUFFER_ASSERT(ringPtr_) assert(RingBufferCheck(ringPtr_))
 
 /*
- * Bit masks used in the sharedFlags field of the ConsoleInfo structure below.
+ * The Win32 console API does not support non-blocking I/O in any form. Thus
+ * the actual calls are made on a separate thread. Moreover, separate
+ * threads are needed for each handle because (for example) blocking on user
+ * input on stdin should not prevent output to stdout when non-blocking i/o
+ * is configured at the script level.
+ *
+ * In the input (e.g. stdin) case, the console stdin thread is the producer
+ * writing to the buffer ring buffer. The Tcl interpreter threads are the
+ * consumer. For the output (e.g. stdout/stderr) case, the Tcl interpreter
+ * are the producers while the console stdout/stderr threads are the
+ * consumers.
+ *
+ * Consoles are identified purely by handles and multiple threads may open
+ * them (as stdin/stdout/stderr are shared).
+ *
+ * Note on reference counting - a ConsoleHandleInfo instance has multiple
+ * references to it - one each from every channel that is attached to it
+ * plus one from the console thread itself which also serves as the reference
+ * from gConsoleHandleInfoList.
  */
-
-#define CONSOLE_EOF	  (1<<2)  /* Console has reached EOF. */
-#define CONSOLE_BUFFERED  (1<<3)  /* Data was read into a buffer by the reader
-				   * thread. */
-
-#define CONSOLE_BUFFER_SIZE (8*1024)
-
-/*
- * Structure containing handles associated with one of the special console
- * threads.
- */
-
-typedef struct {
-    HANDLE thread;		/* Handle to reader or writer thread. */
-    HANDLE readyEvent;		/* Manual-reset event to signal _to_ the main
-				 * thread when the worker thread has finished
-				 * waiting for its normal work to happen. */
-    TclPipeThreadInfo *TI;	/* Thread info structure of writer and reader. */
-} ConsoleThreadInfo;
+typedef struct ConsoleHandleInfo {
+    struct ConsoleHandleInfo *nextPtr; /* Process-global list of consoles */
+    HANDLE console;       /* Console handle */
+    HANDLE consoleThread; /* Handle to thread doing actual i/o on the console */
+    SRWLOCK lock;	  /* Controls access to this structure.
+			   * Cheaper than CRITICAL_SECTION but note does not
+			   * support recursive locks or Try* style attempts.*/
+    CONDITION_VARIABLE consoleThreadCV;/* For awakening console thread */
+    CONDITION_VARIABLE interpThreadCV; /* For awakening interpthread(s) */
+    RingBuffer buffer;	  /* Buffer for data transferred between console
+			   * threads and Tcl threads. For input consoles,
+			   * written by the console thread and read by Tcl
+			   * threads. The converse for output threads */
+    DWORD initMode;	  /* Initial console mode. */
+    DWORD lastError;	  /* An error caused by the last background
+			   * operation. Set to 0 if no error has been
+			   * detected. */
+    int numRefs;	  /* See comments above */
+    int permissions;	  /* TCL_READABLE for input consoles, TCL_WRITABLE
+			   * for output. Only one or the other can be set. */
+} ConsoleHandleInfo;
 
 /*
  * This structure describes per-instance data for a console based channel.
+ *
+ * Note on locking - this structure has no locks because it is accessed
+ * only from the thread owning channel EXCEPT when a console traverses it
+ * looking for a channel that is watching for events on the console. Even
+ * in that case, no locking is required because that access is only under
+ * the consoleLock lock which prevents the channel from being removed from
+ * the gWatchingChannelList which in turn means it will not be deallocated
+ * from under the console thread. Access to individual fields does not need
+ * to be controlled because
+ *   - the console thread does not write to any fields
+ *   - changes to the nextWatchingChannelPtr field and CONSOLE_EVENT_QUEUE
+ *     bit flags are under the gConsoleLock lock
+ *   - changes to other fields do not matter because after being read for
+ *     queueing events, they are verified again when the event is received
+ *     in the interpreter thread (since they could have changed anyways while
+ *     the event was in-flight on the event queue)
+ *
+ * Note on reference counting - a structure instance may be referenced from
+ * three places:
+ *   - the Tcl channel subsystem. This reference is created when on channel
+ *     opening and dropped on channel close. This also covers the reference
+ *     from gWatchingChannelList since queueing / dequeuing from that list
+ *     happens in conjunction with channel operations.
+ *   - the Tcl event queue entries. This reference is added when the event
+ *     is queued and dropped on receipt.
  */
-
-typedef struct ConsoleInfo {
-    HANDLE handle;
-    int type;
-    struct ConsoleInfo *nextPtr;/* Pointer to next registered console. */
+typedef struct ConsoleChannelInfo {
+    HANDLE handle; 		/* Console handle */
+    Tcl_ThreadId threadId;	/* Id of owning thread */
+    struct ConsoleChannelInfo
+	*nextWatchingChannelPtr; /* Pointer to next channel watching events. */
     Tcl_Channel channel;	/* Pointer to channel structure. */
-    int validMask;		/* OR'ed combination of TCL_READABLE,
+    DWORD initMode;		/* Initial console mode. */
+    int numRefs;		/* See comments above */
+    int permissions;            /* OR'ed combination of TCL_READABLE,
 				 * TCL_WRITABLE, or TCL_EXCEPTION: indicates
 				 * which operations are valid on the file. */
     int watchMask;		/* OR'ed combination of TCL_READABLE,
 				 * TCL_WRITABLE, or TCL_EXCEPTION: indicates
 				 * which events should be reported. */
-    int flags;			/* State flags, see above for a list. */
-    Tcl_ThreadId threadId;	/* Thread to which events should be reported.
-				 * This value is used by the reader/writer
-				 * threads. */
-    ConsoleThreadInfo writer;	/* A specialized thread for handling
-				 * asynchronous writes to the console; the
-				 * waiting starts when a control event is sent,
-				 * and a reset event is sent back to the main
-				 * thread when the write is done. */
-    ConsoleThreadInfo reader;	/* A specialized thread for handling
-				 * asynchronous reads from the console; the
-				 * waiting starts when a control event is sent,
-				 * and a reset event is sent back to the main
-				 * thread when input is available. */
-    DWORD writeError;		/* An error caused by the last background
-				 * write. Set to 0 if no error has been
-				 * detected. This word is shared with the
-				 * writer thread so access must be
-				 * synchronized with the writable object. */
-    char *writeBuf;		/* Current background output buffer. Access is
-				 * synchronized with the writable object. */
-    int writeBufLen;		/* Size of write buffer. Access is
-				 * synchronized with the writable object. */
-    int toWrite;		/* Current amount to be written. Access is
-				 * synchronized with the writable object. */
-    int readFlags;		/* Flags that are shared with the reader
-				 * thread. Access is synchronized with the
-				 * readable object. */
-    int bytesRead;		/* Number of bytes in the buffer. */
-    int offset;			/* Number of bytes read out of the buffer. */
-    DWORD initMode;		/* Initial console mode. */
-    char buffer[CONSOLE_BUFFER_SIZE];
-				/* Data consumed by reader thread. */
-} ConsoleInfo;
-
-typedef struct {
-    /*
-     * The following pointer refers to the head of the list of consoles that
-     * are being watched for file events.
-     */
-
-    ConsoleInfo *firstConsolePtr;
-} ThreadSpecificData;
-
-static Tcl_ThreadDataKey dataKey;
+    int flags;			/* State flags */
+#define CONSOLE_EVENT_QUEUED (1 << 0) /* Notification event already queued */
+#define CONSOLE_ASYNC        (1 << 1) /* Channel is non-blocking. */
+#define CONSOLE_READ_OPS     (1 << 2) /* Channel supports read-related ops. */
+} ConsoleChannelInfo;
 
 /*
  * The following structure is what is added to the Tcl event queue when
@@ -126,51 +175,101 @@ static Tcl_ThreadDataKey dataKey;
  */
 
 typedef struct {
-    Tcl_Event header;		/* Information that is standard for all
-				 * events. */
-    ConsoleInfo *infoPtr;	/* Pointer to console info structure. Note
-				 * that we still have to verify that the
-				 * console exists before dereferencing this
-				 * pointer. */
+    Tcl_Event header;	/* Information that is standard for all events. */
+    ConsoleChannelInfo *chanInfoPtr; /* Pointer to console info structure. Note
+				      * that we still have to verify that the
+				      * console exists before dereferencing this
+				      * pointer. */
 } ConsoleEvent;
 
 /*
  * Declarations for functions used only in this file.
  */
 
-static int		ConsoleBlockModeProc(ClientData instanceData,
-			    int mode);
-static void		ConsoleCheckProc(ClientData clientData, int flags);
-static int		ConsoleCloseProc(ClientData instanceData,
-			    Tcl_Interp *interp, int flags);
-static int		ConsoleEventProc(Tcl_Event *evPtr, int flags);
-static void		ConsoleExitHandler(ClientData clientData);
-static int		ConsoleGetHandleProc(ClientData instanceData,
-			    int direction, ClientData *handlePtr);
-static int		ConsoleGetOptionProc(ClientData instanceData,
-			    Tcl_Interp *interp, const char *optionName,
-			    Tcl_DString *dsPtr);
-static void		ConsoleInit(void);
-static int		ConsoleInputProc(ClientData instanceData, char *buf,
-			    int toRead, int *errorCode);
-static int		ConsoleOutputProc(ClientData instanceData,
-			    const char *buf, int toWrite, int *errorCode);
+static int	ConsoleBlockModeProc(ClientData instanceData, int mode);
+static void	ConsoleCheckProc(ClientData clientData, int flags);
+static int	ConsoleCloseProc(ClientData instanceData,
+		    Tcl_Interp *interp, int flags);
+static int	ConsoleEventProc(Tcl_Event *evPtr, int flags);
+static void	ConsoleExitHandler(ClientData clientData);
+static int	ConsoleGetHandleProc(ClientData instanceData,
+		    int direction, ClientData *handlePtr);
+static int	ConsoleGetOptionProc(ClientData instanceData,
+		    Tcl_Interp *interp, const char *optionName,
+		    Tcl_DString *dsPtr);
+static void	ConsoleInit(void);
+static int	ConsoleInputProc(ClientData instanceData, char *buf,
+		    int toRead, int *errorCode);
+static int	ConsoleOutputProc(ClientData instanceData,
+		    const char *buf, int toWrite, int *errorCode);
+static int	ConsoleSetOptionProc(ClientData instanceData,
+		    Tcl_Interp *interp, const char *optionName,
+		    const char *value);
+static void	ConsoleSetupProc(ClientData clientData, int flags);
+static void	ConsoleWatchProc(ClientData instanceData, int mask);
+static void	ProcExitHandler(ClientData clientData);
+static void	ConsoleThreadActionProc(ClientData instanceData, int action);
+static DWORD	ReadConsoleChars(HANDLE hConsole, WCHAR *lpBuffer,
+		    RingSizeT nChars, RingSizeT *nCharsReadPtr);
+static DWORD	WriteConsoleChars(HANDLE hConsole,
+		    const WCHAR *lpBuffer, RingSizeT nChars,
+		    RingSizeT *nCharsWritten);
+static void	RingBufferInit(RingBuffer *ringPtr, RingSizeT capacity);
+static void	RingBufferClear(RingBuffer *ringPtr);
+static char *	RingBufferSegment(const RingBuffer *ringPtr, RingSizeT *lenPtr);
+static int	RingBufferCheck(const RingBuffer *ringPtr);
+static RingSizeT	RingBufferIn(RingBuffer *ringPtr, const char *srcPtr,
+			    RingSizeT srcLen, int partialCopyOk);
+static RingSizeT	RingBufferOut(RingBuffer *ringPtr, char *dstPtr,
+			    RingSizeT dstCapacity, int partialCopyOk);
+static ConsoleHandleInfo *AllocateConsoleHandleInfo(HANDLE consoleHandle,
+			    int permissions);
+static ConsoleHandleInfo *FindConsoleInfo(const ConsoleChannelInfo *);
 static DWORD WINAPI	ConsoleReaderThread(LPVOID arg);
-static int		ConsoleSetOptionProc(ClientData instanceData,
-			    Tcl_Interp *interp, const char *optionName,
-			    const char *value);
-static void		ConsoleSetupProc(ClientData clientData, int flags);
-static void		ConsoleWatchProc(ClientData instanceData, int mask);
 static DWORD WINAPI	ConsoleWriterThread(LPVOID arg);
-static void		ProcExitHandler(ClientData clientData);
-static int		WaitForRead(ConsoleInfo *infoPtr, int blocking);
-static void		ConsoleThreadActionProc(ClientData instanceData,
-			    int action);
-static BOOL		ReadConsoleBytes(HANDLE hConsole, LPVOID lpBuffer,
-			    DWORD nbytes, LPDWORD nbytesread);
-static BOOL		WriteConsoleBytes(HANDLE hConsole,
-			    const void *lpBuffer, DWORD nbytes,
-			    LPDWORD nbyteswritten);
+#ifdef OBSOLETE
+static int	WaitForRead(ConsoleChannelInfo *infoPtr, int blocking);
+#endif
+
+/*
+ * Static data.
+ */
+
+typedef struct {
+    /* Currently this struct is only used to detect thread initialization */
+    int notUsed; /* Dummy field */
+} ThreadSpecificData;
+static Tcl_ThreadDataKey dataKey;
+
+/*
+ * All access to static data is controlled through a single process-wide
+ * lock. A process can have only a single console at a time, with three
+ * handles for stdin, stdout and stderr. Creation/destruction of consoles is
+ * a relatively rare event (currently only possible during process start),
+ * the number of consoles (as opposed to channels) is small (only stdin,
+ * stdout and stderr), and contention low. More finer-grained locking would
+ * likely not only complicate implementation but be slower due to multiple
+ * locks being held. Note console channels also differ from other Tcl
+ * channel types in that the channel<->OS descriptor mapping is not one-to-one.
+ *
+ * The gConsoleLock locks around access to the initialized variable, and it
+ * is used to protect background threads from being terminated while they
+ * are using APIs that hold locks. TBD - is this still true?
+ */
+SRWLOCK gConsoleLock;
+
+
+/* Process-wide list of console handles. Access control through gConsoleLock */
+static ConsoleHandleInfo *gConsoleHandleInfoList;
+
+/*
+ * Process-wide list of channels that are listening for events. Again access
+ * control through gConsoleLock. Common list for all threads is simplifies
+ * locking and bookkeeping and is workable because in practice multiple
+ * threads are very unlikely to be all waiting on stdin (not workable
+ * because input would be randomly distributed to threads)
+ */
+static ConsoleChannelInfo *gWatchingChannelList;
 
 /*
  * This structure describes the channel type structure for command console
@@ -178,82 +277,350 @@ static BOOL		WriteConsoleBytes(HANDLE hConsole,
  */
 
 static const Tcl_ChannelType consoleChannelType = {
-    "console",			/* Type name. */
-    TCL_CHANNEL_VERSION_5,	/* v5 channel */
-    TCL_CLOSE2PROC,		/* Close proc. */
-    ConsoleInputProc,		/* Input proc. */
-    ConsoleOutputProc,		/* Output proc. */
-    NULL,			/* Seek proc. */
-    ConsoleSetOptionProc,	/* Set option proc. */
-    ConsoleGetOptionProc,	/* Get option proc. */
-    ConsoleWatchProc,		/* Set up notifier to watch the channel. */
-    ConsoleGetHandleProc,	/* Get an OS handle from channel. */
-    ConsoleCloseProc,		/* close2proc. */
-    ConsoleBlockModeProc,	/* Set blocking or non-blocking mode. */
-    NULL,			/* Flush proc. */
-    NULL,			/* Handler proc. */
-    NULL,			/* Wide seek proc. */
-    ConsoleThreadActionProc,	/* Thread action proc. */
-    NULL			/* Truncation proc. */
+    "console",               /* Type name. */
+    TCL_CHANNEL_VERSION_5,   /* v5 channel */
+    TCL_CLOSE2PROC,          /* Close proc. */
+    ConsoleInputProc,        /* Input proc. */
+    ConsoleOutputProc,       /* Output proc. */
+    NULL,                    /* Seek proc. */
+    ConsoleSetOptionProc,    /* Set option proc. */
+    ConsoleGetOptionProc,    /* Get option proc. */
+    ConsoleWatchProc,        /* Set up notifier to watch the channel. */
+    ConsoleGetHandleProc,    /* Get an OS handle from channel. */
+    ConsoleCloseProc,        /* close2proc. */
+    ConsoleBlockModeProc,    /* Set blocking or non-blocking mode. */
+    NULL,                    /* Flush proc. */
+    NULL,                    /* Handler proc. */
+    NULL,                    /* Wide seek proc. */
+    ConsoleThreadActionProc, /* Thread action proc. */
+    NULL                     /* Truncation proc. */
 };
+
+/*
+ *------------------------------------------------------------------------
+ *
+ * RingBufferInit --
+ *
+ *    Initializes the ring buffer to a given size.
+ *
+ * Results:
+ *    None.
+ *
+ * Side effects:
+ *    Panics on allocation failure.
+ *
+ *------------------------------------------------------------------------
+ */
+static void
+RingBufferInit(RingBuffer *ringPtr, RingSizeT capacity)
+{
+    if (capacity <= 0 || capacity > RingSizeT_MAX) {
+	Tcl_Panic("Internal error: invalid ring buffer capacity requested.");
+    }
+    ringPtr->bufPtr = (char *)ckalloc(capacity);
+    ringPtr->capacity = capacity;
+    ringPtr->start    = 0;
+    ringPtr->length   = 0;
+}
 
 /*
- *----------------------------------------------------------------------
+ *------------------------------------------------------------------------
  *
- * ReadConsoleBytes, WriteConsoleBytes --
+ * RingBufferClear
  *
- *	Wrapper for ReadConsoleW, that takes and returns number of bytes
- *	instead of number of WCHARS.
+ *    Clears the contents of a ring buffer.
  *
- *----------------------------------------------------------------------
+ * Results:
+ *    None.
+ *
+ * Side effects:
+ *    The allocated internal buffer is freed.
+ *
+ *------------------------------------------------------------------------
+ */
+static void
+RingBufferClear(RingBuffer *ringPtr)
+{
+    if (ringPtr->bufPtr) {
+	ckfree(ringPtr->bufPtr);
+	ringPtr->bufPtr = NULL;
+    }
+    ringPtr->capacity = 0;
+    ringPtr->start    = 0;
+    ringPtr->length   = 0;
+}
+
+/*
+ *------------------------------------------------------------------------
+ *
+ * RingBufferIn --
+ *
+ *    Appends data to the ring buffer.
+ *
+ * Results:
+ *    Returns number of bytes copied.
+ *
+ * Side effects:
+ *    Internal buffer is updated.
+ *
+ *------------------------------------------------------------------------
+ */
+static RingSizeT
+RingBufferIn(
+    RingBuffer *ringPtr,
+    const char *srcPtr, /* Source to be copied */
+    RingSizeT srcLen,	  /* Length of source */
+    int partialCopyOk 		  /* If true, partial copy is permitted */
+    )
+{
+    RingSizeT freeSpace;
+    RingSizeT endSpace;
+
+    RINGBUFFER_ASSERT(ringPtr);
+
+    freeSpace = ringPtr->capacity - ringPtr->length;
+    if (freeSpace < srcLen) {
+	if (!partialCopyOk) {
+	    return 0;
+	}
+	/* Copy only as much as free space allows */
+	srcLen = freeSpace;
+    }
+
+    /* Copy as much as possible to the tail */
+    if (ringPtr->capacity - ringPtr->start > ringPtr->length) {
+	/* There is room at the back */
+	RingSizeT endSpaceStart = ringPtr->start + ringPtr->length;
+	endSpace = ringPtr->capacity - endSpaceStart;
+	if (endSpace > srcLen) {
+	    endSpace = srcLen;
+	}
+	memmove(endSpaceStart + ringPtr->bufPtr, srcPtr, endSpace);
+    }
+    else {
+	endSpace = 0;
+    }
+
+    /* Wrap around any left over data. Have already copied endSpace bytes */
+    if (srcLen > endSpace) {
+	memmove(ringPtr->bufPtr, endSpace + srcPtr, srcLen - endSpace);
+    }
+
+    ringPtr->length += srcLen;
+
+    RINGBUFFER_ASSERT(ringPtr);
+
+    return srcLen;
+}
+
+/*
+ *------------------------------------------------------------------------
+ *
+ * RingBufferOut --
+ *
+ *    Moves data out of the ring buffer.  If dstPtr is NULL, the data
+ *    is simply removed.
+ *
+ * Results:
+ *    Returns number of bytes copied or removed.
+ *
+ * Side effects:
+ *    Internal buffer is updated.
+ *
+ *------------------------------------------------------------------------
+ */
+static RingSizeT
+RingBufferOut(RingBuffer *ringPtr,
+	      char *dstPtr,	      /* Buffer for output data. May be NULL */
+	      RingSizeT dstCapacity,  /* Size of buffer */
+	      int partialCopyOk)      /* If true, return what's available */
+{
+    RingSizeT leadLen;
+
+    RINGBUFFER_ASSERT(ringPtr);
+
+    if (dstCapacity > ringPtr->length) {
+	if (dstPtr && !partialCopyOk) {
+	    return 0;
+	}
+	dstCapacity = ringPtr->length;
+    }
+
+    if (ringPtr->start <= (ringPtr->capacity - ringPtr->length)) {
+	/* No content wrap around. So leadLen is entire content */
+	leadLen = ringPtr->length;
+    }
+    else {
+	/* Content wraps around so lead segment stretches to end of buffer */
+	leadLen = ringPtr->capacity - ringPtr->start;
+    }
+    if (leadLen >= dstCapacity) {
+	if (dstPtr) {
+	    memmove(dstPtr, ringPtr->start + ringPtr->bufPtr, dstCapacity);
+	}
+	ringPtr->start += dstCapacity;
+    }
+    else {
+	RingSizeT wrapLen = dstCapacity - leadLen;
+	if (dstPtr) {
+	    memmove(dstPtr,
+		    ringPtr->start + ringPtr->bufPtr,
+		    leadLen);
+	    memmove(
+		leadLen + dstPtr, ringPtr->bufPtr, wrapLen);
+	}
+	ringPtr->start = wrapLen;
+    }
+
+    ringPtr->length -= dstCapacity;
+    if (ringPtr->start == ringPtr->capacity || ringPtr->length == 0) {
+	ringPtr->start = 0;
+    }
+
+    RINGBUFFER_ASSERT(ringPtr);
+
+    return dstCapacity;
+}
+
+/*
+ *------------------------------------------------------------------------
+ *
+ * RingBufferSegment --
+ *
+ *    Returns a pointer to the leading data segment in the ring buffer.
+ *
+ * Results:
+ *    Pointer to start of segment.
+ *
+ * Side effects:
+ *    None.
+ *
+ *------------------------------------------------------------------------
  */
+ static char *
+ RingBufferSegment(const RingBuffer *ringPtr, RingSizeT *lengthPtr)
+{
+    RINGBUFFER_ASSERT(ringPtr);
+    if (ringPtr->length <= (ringPtr->capacity - ringPtr->start)) {
+	/* No content wrap around. */
+	*lengthPtr = ringPtr->length;
+    }
+    else {
+	/* Content wraps around so lead segment stretches to end of buffer */
+	*lengthPtr = ringPtr->capacity - ringPtr->start;
+    }
+    return *lengthPtr == 0 ? NULL : ringPtr->start + ringPtr->bufPtr;
+}
+
+static int
+RingBufferCheck(const RingBuffer *ringPtr)
+{
+    return (ringPtr->bufPtr != NULL && ringPtr->capacity == CONSOLE_BUFFER_SIZE
+	    && ringPtr->start < ringPtr->capacity
+	    && ringPtr->length <= ringPtr->capacity);
+}
 
-static BOOL
-ReadConsoleBytes(
+/*
+ *------------------------------------------------------------------------
+ *
+ * ReadConsoleChars --
+ *
+ *    Wrapper for ReadConsoleW.
+ *
+ * Results:
+ *    Returns 0 on success, else Windows error code.
+ *
+ * Side effects:
+ *    On success the number of characters (not bytes) read is stored in
+ *    *nCharsReadPtr. This will be 0 if the operation was interrupted by
+ *    a Ctrl-C or a CancelIo call.
+ *
+ *------------------------------------------------------------------------
+ */
+static DWORD
+ReadConsoleChars(
     HANDLE hConsole,
-    LPVOID lpBuffer,
-    DWORD nbytes,
-    LPDWORD nbytesread)
+    WCHAR *lpBuffer,
+    RingSizeT nChars,
+    RingSizeT *nCharsReadPtr)
 {
-    DWORD ntchars;
+    DWORD nRead;
     BOOL result;
 
     /*
-     * If user types a Ctrl-Break or Ctrl-C, ReadConsole will return
-     * success with ntchars == 0 and GetLastError() will be
-     * ERROR_OPERATION_ABORTED. We do not want to treat this case
-     * as EOF so we will loop around again. If no Ctrl signal handlers
-     * have been established, the default signal OS handler in a separate
-     * thread will terminate the program. If a Ctrl signal handler
-     * has been established (through an extension for example), it
-     * will run and take whatever action it deems appropriate.
+     * If user types a Ctrl-Break or Ctrl-C, ReadConsole will return success
+     * with ntchars == 0 and GetLastError() will be ERROR_OPERATION_ABORTED.
+     * If no Ctrl signal handlers have been established, the default signal
+     * OS handler in a separate thread will terminate the program. If a Ctrl
+     * signal handler has been established (through an extension for
+     * example), it will run and take whatever action it deems appropriate.
+     *
+     * If one thread closes its channel, it calls CancelSynchronousIo on the
+     * console handle which results again in success being returned and
+     * GetLastError() being ERROR_OPERATION_ABORTED but ntchars in
+     * unmodified.
+     *
+     * In both cases above we will return success but with nbytesread as 0.
+     * This allows caller to check for thread termination etc.
+     *
+     * See https://bugs.python.org/issue30237
+     * or https://github.com/microsoft/terminal/issues/12143
      */
-    do {
-        result = ReadConsoleW(hConsole, lpBuffer, nbytes / sizeof(WCHAR), &ntchars,
-                             NULL);
-    } while (result && ntchars == 0 && GetLastError() == ERROR_OPERATION_ABORTED);
-    if (nbytesread != NULL) {
-	*nbytesread = ntchars * sizeof(WCHAR);
-    }
-    return result;
+    nRead = (DWORD)-1;
+    result = ReadConsoleW(hConsole, lpBuffer, nChars, &nRead, NULL);
+    if (result) {
+	if ((nRead == 0 || nRead == (DWORD)-1)
+	    && GetLastError() == ERROR_OPERATION_ABORTED) {
+	    nRead = 0;
+	}
+	*nCharsReadPtr = nRead;
+	return 0;
+    }
+    else
+	return GetLastError();
 }
+
+/*
+ *------------------------------------------------------------------------
+ *
+ * WriteConsoleChars --
+ *
+ *    Wrapper for WriteConsoleW.
+ *
+ * Results:
+ *    Returns 0 on success, Windows error code on failure.
+ *
+ * Side effects:
+ *    On success the number of characters (not bytes) written is stored in
+ *    *nCharsWrittenPtr. This will be 0 if the operation was interrupted by
+ *    a Ctrl-C or a CancelIo call.
+ *
+ *------------------------------------------------------------------------
+ */
 
-static BOOL
-WriteConsoleBytes(
+static DWORD
+WriteConsoleChars(
     HANDLE hConsole,
-    const void *lpBuffer,
-    DWORD nbytes,
-    LPDWORD nbyteswritten)
+    const WCHAR *lpBuffer,
+    RingSizeT nChars,
+    RingSizeT *nCharsWrittenPtr)
 {
-    DWORD ntchars;
+    DWORD nCharsWritten;
     BOOL result;
 
-    result = WriteConsoleW(hConsole, lpBuffer, nbytes / sizeof(WCHAR), &ntchars,
-	    NULL);
-    if (nbyteswritten != NULL) {
-	*nbyteswritten = ntchars * sizeof(WCHAR);
+    /* See comments in ReadConsoleChars, not sure that applies here */
+    nCharsWritten = (DWORD)-1;
+    result = WriteConsoleW(hConsole, lpBuffer, nChars, &nCharsWritten, NULL);
+    if (result) {
+	if (nCharsWritten == (DWORD) -1) {
+	    nCharsWritten = 0;
+	}
+	*nCharsWrittenPtr = nCharsWritten;
+	return 0;
+    }
+    else {
+	return GetLastError();
     }
-    return result;
 }
 
 /*
@@ -281,18 +648,18 @@ ConsoleInit(void)
      */
 
     if (!initialized) {
-	Tcl_MutexLock(&consoleMutex);
+	AcquireSRWLockExclusive(&gConsoleLock);
 	if (!initialized) {
 	    initialized = 1;
 	    Tcl_CreateExitHandler(ProcExitHandler, NULL);
 	}
-	Tcl_MutexUnlock(&consoleMutex);
+	ReleaseSRWLockExclusive(&gConsoleLock);
     }
 
     if (TclThreadDataKeyGet(&dataKey) == NULL) {
 	ThreadSpecificData *tsdPtr = TCL_TSD_INIT(&dataKey);
 
-	tsdPtr->firstConsolePtr = NULL;
+	tsdPtr->notUsed = 0;
 	Tcl_CreateEventSource(ConsoleSetupProc, ConsoleCheckProc, NULL);
 	Tcl_CreateThreadExitHandler(ConsoleExitHandler, NULL);
     }
@@ -343,9 +710,9 @@ static void
 ProcExitHandler(
     TCL_UNUSED(ClientData))
 {
-    Tcl_MutexLock(&consoleMutex);
+    AcquireSRWLockExclusive(&gConsoleLock);
     initialized = 0;
-    Tcl_MutexUnlock(&consoleMutex);
+    ReleaseSRWLockExclusive(&gConsoleLock);
 }
 
 /*
@@ -354,7 +721,9 @@ ProcExitHandler(
  * ConsoleSetupProc --
  *
  *	This procedure is invoked before Tcl_DoOneEvent blocks waiting for an
- *	event.
+ *	event. It walks the channel list and if any input channel has data
+ *      available or output channel has space for data, sets the event loop
+ *      blocking time to 0 so that it will poll immediately.
  *
  * Results:
  *	None.
@@ -370,34 +739,40 @@ ConsoleSetupProc(
     TCL_UNUSED(ClientData),
     int flags)			/* Event flags as passed to Tcl_DoOneEvent. */
 {
-    ConsoleInfo *infoPtr;
+    ConsoleChannelInfo *chanInfoPtr;
     Tcl_Time blockTime = { 0, 0 };
     int block = 1;
-    ThreadSpecificData *tsdPtr = TCL_TSD_INIT(&dataKey);
 
     if (!(flags & TCL_FILE_EVENTS)) {
 	return;
     }
 
     /*
-     * Look to see if any events are already pending. If they are, poll.
+     * Walk the list of channels. See general comments for struct
+     * ConsoleChannelInfo with regard to locking and field access.
      */
-
-    for (infoPtr = tsdPtr->firstConsolePtr; infoPtr != NULL;
-	    infoPtr = infoPtr->nextPtr) {
-	if (infoPtr->watchMask & TCL_WRITABLE) {
-	    if (WaitForSingleObject(infoPtr->writer.readyEvent,
-		    0) != WAIT_TIMEOUT) {
-		block = 0;
+    AcquireSRWLockShared(&gConsoleLock); /* READ lock - no data modification */
+
+    for (chanInfoPtr = gWatchingChannelList; block && chanInfoPtr != NULL;
+	 chanInfoPtr = chanInfoPtr->nextWatchingChannelPtr) {
+	ConsoleHandleInfo *handleInfoPtr;
+	handleInfoPtr = FindConsoleInfo(chanInfoPtr);
+	if (handleInfoPtr != NULL) {
+	    AcquireSRWLockShared(&handleInfoPtr->lock);
+	    if ((chanInfoPtr->watchMask & TCL_READABLE)
+		&& RingBufferLength(&handleInfoPtr->buffer) > 0) {
+		block = 0; /* Input data available */
 	    }
-	}
-	if (infoPtr->watchMask & TCL_READABLE) {
-	    if (WaitForRead(infoPtr, 0) >= 0) {
-		block = 0;
+	    else if (RingBufferFreeSpace(&handleInfoPtr->buffer) > 0) {
+		block = 0; /* Output space available */
 	    }
+	    ReleaseSRWLockShared(&handleInfoPtr->lock);
 	}
     }
+    ReleaseSRWLockShared(&gConsoleLock);
+
     if (!block) {
+	/* At least one channel is readable/writable. Set block time to 0 */
 	Tcl_SetMaxBlockTime(&blockTime);
     }
 }
@@ -424,54 +799,69 @@ ConsoleCheckProc(
     TCL_UNUSED(ClientData),
     int flags)			/* Event flags as passed to Tcl_DoOneEvent. */
 {
-    ConsoleInfo *infoPtr;
+    ConsoleChannelInfo *chanInfoPtr;
+    Tcl_ThreadId me;
     int needEvent;
-    ThreadSpecificData *tsdPtr = TCL_TSD_INIT(&dataKey);
 
     if (!(flags & TCL_FILE_EVENTS)) {
 	return;
     }
 
+    me = Tcl_GetCurrentThread();
+
     /*
-     * Queue events for any ready consoles that don't already have events
-     * queued.
+     * Acquire a shared lock. Note this is ok even though we potentially
+     * modify the chanInfoPtr->flags because chanInfoPtr is only modified
+     * when it belongs to this thread and no other thread will write to it.
+     * THe shared lock is intended to protect the global gWatchingChannelList
+     * as we traverse it.
      */
+    AcquireSRWLockShared(&gConsoleLock);
+
+    for (chanInfoPtr = gWatchingChannelList; chanInfoPtr != NULL;
+	    chanInfoPtr = chanInfoPtr->nextWatchingChannelPtr) {
+	ConsoleHandleInfo *handleInfoPtr;
 
-    for (infoPtr = tsdPtr->firstConsolePtr; infoPtr != NULL;
-	    infoPtr = infoPtr->nextPtr) {
-	if (infoPtr->flags & CONSOLE_PENDING) {
+	if (chanInfoPtr->threadId != me) {
+	    /* Some other thread owns the channel */
+	    continue;
+	}
+	if (chanInfoPtr->flags & CONSOLE_EVENT_QUEUED) {
+	    /* A notification event already queued. No point in another. */
 	    continue;
 	}
 
-	/*
-	 * Queue an event if the console is signaled for reading or writing.
-	 */
+	handleInfoPtr = FindConsoleInfo(chanInfoPtr);
+	/* Pointer is safe to access as we are holding gConsoleLock */
 
-	needEvent = 0;
-	if (infoPtr->watchMask & TCL_WRITABLE) {
-	    if (WaitForSingleObject(infoPtr->writer.readyEvent,
-		    0) != WAIT_TIMEOUT) {
-		needEvent = 1;
+	if (handleInfoPtr != NULL) {
+	    AcquireSRWLockShared(&handleInfoPtr->lock);
+	    if ((chanInfoPtr->watchMask & TCL_READABLE)
+		&& RingBufferLength(&handleInfoPtr->buffer) > 0) {
+		needEvent = 1; /* Input data available */
 	    }
-	}
-
-	if (infoPtr->watchMask & TCL_READABLE) {
-	    if (WaitForRead(infoPtr, 0) >= 0) {
-		needEvent = 1;
+	    else if (RingBufferFreeSpace(&handleInfoPtr->buffer) > 0) {
+		needEvent = 1; /* Output space available */
 	    }
+	    ReleaseSRWLockShared(&handleInfoPtr->lock);
 	}
 
 	if (needEvent) {
 	    ConsoleEvent *evPtr = (ConsoleEvent *)ckalloc(sizeof(ConsoleEvent));
 
-	    infoPtr->flags |= CONSOLE_PENDING;
+	    /* See note above loop why this can be accessed without locks */
+	    chanInfoPtr->flags |= CONSOLE_EVENT_QUEUED;
+	    chanInfoPtr->numRefs += 1; /* So it does not go away while event
+					  is in queue */
 	    evPtr->header.proc = ConsoleEventProc;
-	    evPtr->infoPtr = infoPtr;
+	    evPtr->chanInfoPtr = chanInfoPtr;
 	    Tcl_QueueEvent((Tcl_Event *) evPtr, TCL_QUEUE_TAIL);
 	}
     }
+
+    ReleaseSRWLockShared(&gConsoleLock);
 }
-
+
 /*
  *----------------------------------------------------------------------
  *
@@ -494,7 +884,7 @@ ConsoleBlockModeProc(
     int mode)			/* TCL_MODE_BLOCKING or
 				 * TCL_MODE_NONBLOCKING. */
 {
-    ConsoleInfo *infoPtr = (ConsoleInfo *)instanceData;
+    ConsoleChannelInfo *chanInfoPtr = (ConsoleChannelInfo *)instanceData;
 
     /*
      * Consoles on Windows can not be switched between blocking and
@@ -505,9 +895,9 @@ ConsoleBlockModeProc(
      */
 
     if (mode == TCL_MODE_NONBLOCKING) {
-	infoPtr->flags |= CONSOLE_ASYNC;
+	chanInfoPtr->flags |= CONSOLE_ASYNC;
     } else {
-	infoPtr->flags &= ~CONSOLE_ASYNC;
+	chanInfoPtr->flags &= ~CONSOLE_ASYNC;
     }
     return 0;
 }
@@ -530,102 +920,86 @@ ConsoleBlockModeProc(
 
 static int
 ConsoleCloseProc(
-    ClientData instanceData,	/* Pointer to ConsoleInfo structure. */
+    ClientData instanceData,	/* Pointer to ConsoleChannelInfo structure. */
     TCL_UNUSED(Tcl_Interp *),
     int flags)
 {
-    ConsoleInfo *consolePtr = (ConsoleInfo *)instanceData;
+    ConsoleChannelInfo *chanInfoPtr = (ConsoleChannelInfo *)instanceData;
+    ConsoleHandleInfo *handleInfoPtr;
     int errorCode = 0;
-    ConsoleInfo *infoPtr, **nextPtrPtr;
-    ThreadSpecificData *tsdPtr = TCL_TSD_INIT(&dataKey);
+    ConsoleChannelInfo **nextPtrPtr;
 
     if ((flags & (TCL_CLOSE_READ | TCL_CLOSE_WRITE)) != 0) {
 	return EINVAL;
     }
 
-    /*
-     * Clean up the background thread if necessary. Note that this must be
-     * done before we can close the file, since the thread may be blocking
-     * trying to read from the console.
-     */
+    AcquireSRWLockExclusive(&gConsoleLock);
 
-    if (consolePtr->reader.thread) {
-	TclPipeThreadStop(&consolePtr->reader.TI, consolePtr->reader.thread);
-	CloseHandle(consolePtr->reader.thread);
-	CloseHandle(consolePtr->reader.readyEvent);
-	consolePtr->reader.thread = NULL;
+    /* Remove channel from watchers' list */
+    for (nextPtrPtr = &gWatchingChannelList; *nextPtrPtr != NULL;
+	 nextPtrPtr = &(*nextPtrPtr)->nextWatchingChannelPtr) {
+	if (*nextPtrPtr == (ConsoleChannelInfo *) chanInfoPtr) {
+	    *nextPtrPtr = (*nextPtrPtr)->nextWatchingChannelPtr;
+	    break;
+	}
     }
-    consolePtr->validMask &= ~TCL_READABLE;
 
-    /*
-     * Wait for the writer thread to finish the current buffer, then terminate
-     * the thread and close the handles. If the channel is nonblocking, there
-     * should be no pending write operations.
-     */
-
-    if (consolePtr->writer.thread) {
-	if (consolePtr->toWrite) {
-	    /*
-	     * We only need to wait if there is something to write. This may
-	     * prevent infinite wait on exit. [Python Bug 216289]
-	     */
+    handleInfoPtr = FindConsoleInfo(chanInfoPtr);
+    if (handleInfoPtr) {
+	/*
+	 * Console thread may be blocked either waiting for console i/o
+	 * or waiting on the condition variable for buffer empty/full
+	 */
+	AcquireSRWLockShared(&handleInfoPtr->lock);
 
-	    WaitForSingleObject(consolePtr->writer.readyEvent, 5000);
-	}
+	handleInfoPtr->numRefs -= 1; /* Remove reference from this channel */
 
-	TclPipeThreadStop(&consolePtr->writer.TI, consolePtr->writer.thread);
-	CloseHandle(consolePtr->writer.thread);
-	CloseHandle(consolePtr->writer.readyEvent);
-	consolePtr->writer.thread = NULL;
-    }
-    consolePtr->validMask &= ~TCL_WRITABLE;
+	/* Break the thread out of blocking console i/o */
+	CancelSynchronousIo(handleInfoPtr->consoleThread);
 
-    /*
-     * If the user has been tinkering with the mode, reset it now. We ignore
-     * any errors from this; we're quite possibly about to close or exit
-     * anyway.
-     */
+	/* Wake up the console handling thread */
+	WakeConditionVariable(&handleInfoPtr->consoleThreadCV);
 
-    if ((consolePtr->flags & CONSOLE_READ_OPS) &&
-	    (consolePtr->flags & CONSOLE_RESET)) {
-	SetConsoleMode(consolePtr->handle, consolePtr->initMode);
+	ReleaseSRWLockShared(&handleInfoPtr->lock);
     }
 
-    /*
-     * Don't close the Win32 handle if the handle is a standard channel during
-     * the thread exit process. Otherwise, one thread may kill the stdio of
-     * another.
-     */
+    ReleaseSRWLockExclusive(&gConsoleLock);
 
-    if (!TclInThreadExit()
-	    || ((GetStdHandle(STD_INPUT_HANDLE) != consolePtr->handle)
-		&& (GetStdHandle(STD_OUTPUT_HANDLE) != consolePtr->handle)
-		&& (GetStdHandle(STD_ERROR_HANDLE) != consolePtr->handle))) {
-	if (CloseHandle(consolePtr->handle) == FALSE) {
-	    Tcl_WinConvertError(GetLastError());
-	    errorCode = errno;
+    chanInfoPtr->channel = NULL;
+    chanInfoPtr->watchMask   = 0;
+    chanInfoPtr->permissions = 0;
+
+    if (chanInfoPtr->handle) {
+	/*
+	 * Don't close the Win32 handle if the handle is a standard channel
+	 * during the thread exit process. Otherwise, one thread may kill the
+	 * stdio of another. TODO - an explicit close in script will still close
+	 * it.
+	 */
+	if (!TclInThreadExit()
+	    || ((GetStdHandle(STD_INPUT_HANDLE) != chanInfoPtr->handle)
+		&& (GetStdHandle(STD_OUTPUT_HANDLE) != chanInfoPtr->handle)
+		&& (GetStdHandle(STD_ERROR_HANDLE) != chanInfoPtr->handle))) {
+	    if (CloseHandle(chanInfoPtr->handle) == FALSE) {
+		Tcl_WinConvertError(GetLastError());
+		errorCode = errno;
+	    }
 	}
+	chanInfoPtr->handle = NULL;
     }
 
-    consolePtr->watchMask &= consolePtr->validMask;
-
     /*
-     * Remove the file from the list of watched files.
+     * Note, we can check and manipulate numRefs without a lock because
+     * we have removed it from the watch queue so the console thread cannot
+     * get at it.
      */
-
-    for (nextPtrPtr = &tsdPtr->firstConsolePtr, infoPtr = *nextPtrPtr;
-	    infoPtr != NULL;
-	    nextPtrPtr = &infoPtr->nextPtr, infoPtr = *nextPtrPtr) {
-	if (infoPtr == (ConsoleInfo *) consolePtr) {
-	    *nextPtrPtr = infoPtr->nextPtr;
-	    break;
-	}
+    if (chanInfoPtr->numRefs > 1) {
+	/* There may be references already on the event queue */
+	chanInfoPtr->numRefs -= 1;
     }
-    if (consolePtr->writeBuf != NULL) {
-	ckfree(consolePtr->writeBuf);
-	consolePtr->writeBuf = 0;
+    else {
+	ckfree(chanInfoPtr);
     }
-    ckfree(consolePtr);
 
     return errorCode;
 }
@@ -647,80 +1021,85 @@ ConsoleCloseProc(
  *
  *----------------------------------------------------------------------
  */
-
 static int
 ConsoleInputProc(
     ClientData instanceData,	/* Console state. */
-    char *buf,			/* Where to store data read. */
+    char *bufPtr,		/* Where to store data read. */
     int bufSize,		/* How much space is available in the
 				 * buffer? */
     int *errorCode)		/* Where to store error code. */
 {
-    ConsoleInfo *infoPtr = (ConsoleInfo *)instanceData;
-    DWORD count, bytesRead = 0;
-    int result;
+    ConsoleChannelInfo *chanInfoPtr = (ConsoleChannelInfo *)instanceData;
+    ConsoleHandleInfo *handleInfoPtr;
+    RingSizeT numRead;
 
     *errorCode = 0;
 
-    /*
-     * Synchronize with the reader thread.
-     */
-
-    result = WaitForRead(infoPtr, (infoPtr->flags & CONSOLE_ASYNC) ? 0 : 1);
-
-    /*
-     * If an error occurred, return immediately.
-     */
-
-    if (result == -1) {
-	*errorCode = errno;
-	return -1;
+    AcquireSRWLockShared(&gConsoleLock);
+    handleInfoPtr = FindConsoleInfo(chanInfoPtr);
+    if (handleInfoPtr == NULL) {
+	/* Really shouldn't happen since channel is holding a reference */
+	ReleaseSRWLockShared(&gConsoleLock);
+	return 0; /* EOF */
     }
+    AcquireSRWLockExclusive(&handleInfoPtr->lock);
+    ReleaseSRWLockShared(&gConsoleLock); /* AFTER acquiring handleInfoPtr->lock */
 
-    if (infoPtr->readFlags & CONSOLE_BUFFERED) {
+    numRead = RingBufferOut(&handleInfoPtr->buffer, bufPtr, bufSize, 1);
+    while (numRead == 0) {
 	/*
-	 * Data is stored in the buffer.
+	 * No data available.
+	 *  - If an error was recorded, generate that and reset it.
+	 *  - If EOF, indicate as much. TODO - can console thread still be
+	 * running in that case?
+	 *  - Otherwise, if non-blocking return EAGAIN or wait for more data.
 	 */
-
-	if (bufSize < (infoPtr->bytesRead - infoPtr->offset)) {
-	    memcpy(buf, &infoPtr->buffer[infoPtr->offset], bufSize);
-	    bytesRead = bufSize;
-	    infoPtr->offset += bufSize;
-	} else {
-	    memcpy(buf, &infoPtr->buffer[infoPtr->offset], bufSize);
-	    bytesRead = infoPtr->bytesRead - infoPtr->offset;
-
-	    /*
-	     * Reset the buffer.
-	     */
-
-	    infoPtr->readFlags &= ~CONSOLE_BUFFERED;
-	    infoPtr->offset = 0;
+	if (handleInfoPtr->lastError != 0) {
+	    Tcl_WinConvertError(handleInfoPtr->lastError);
+	    handleInfoPtr->lastError = 0;
+	    *errorCode = Tcl_GetErrno();
+	    numRead    = -1;
+	}
+	else if (handleInfoPtr->console == NULL) {
+	    /* EOF - break with numRead == 0 */
+	    break;
+	}
+	else {
+	    if (chanInfoPtr->flags & CONSOLE_ASYNC) {
+		*errorCode = EAGAIN;
+		numRead    = -1;
+	    }
+	    else {
+		/*
+		 * Release the lock and sleep. Note that because the channel
+		 * holds a reference count on handleInfoPtr, it will not
+		 * be deallocated while the lock is released.
+		 */
+		WakeConditionVariable(&handleInfoPtr->consoleThreadCV);
+		if (SleepConditionVariableSRW(&handleInfoPtr->interpThreadCV,
+					      &handleInfoPtr->lock,
+					      INFINITE,
+					      0)) {
+		    /*
+		     * Lock is reacquired. However, in the meanwhile another
+		     * thread could have consumed data. So loop continues
+		     * with check of numRead value.
+		     */
+		    numRead = RingBufferOut(
+			&handleInfoPtr->buffer, bufPtr, bufSize, 1);
+		}
+		else {
+		    /* Report the error */
+		    Tcl_WinConvertError(GetLastError());
+		    *errorCode = Tcl_GetErrno();
+		    numRead    = -1;
+		}
+	    }
 	}
-
-	return bytesRead;
-    }
-
-    /*
-     * Attempt to read bufSize bytes. The read will return immediately if
-     * there is any data available. Otherwise it will block until at least one
-     * byte is available or an EOF occurs.
-     */
-
-    if (ReadConsoleBytes(infoPtr->handle, (LPVOID) buf, (DWORD) bufSize,
-	    &count) == TRUE) {
-	/*
-	 * TODO: This potentially writes beyond the limits specified
-	 * by the caller.  In practice this is harmless, since all writes
-	 * are into ChannelBuffers, and those have padding, but still
-	 * ought to remove this, unless some Windows wizard can give
-	 * a reason not to.
-	 */
-	buf[count] = '\0';
-	return count;
     }
 
-    return -1;
+    ReleaseSRWLockExclusive(&handleInfoPtr->lock);
+    return numRead;
 }
 
 /*
@@ -740,7 +1119,6 @@ ConsoleInputProc(
  *
  *----------------------------------------------------------------------
  */
-
 static int
 ConsoleOutputProc(
     ClientData instanceData,	/* Console state. */
@@ -748,74 +1126,70 @@ ConsoleOutputProc(
     int toWrite,		/* How many bytes to write? */
     int *errorCode)		/* Where to store error code. */
 {
-    ConsoleInfo *infoPtr = (ConsoleInfo *)instanceData;
-    ConsoleThreadInfo *threadInfo = &infoPtr->writer;
-    DWORD bytesWritten, timeout;
+    ConsoleChannelInfo *chanInfoPtr = (ConsoleChannelInfo *)instanceData;
+    ConsoleHandleInfo *handleInfoPtr;
+    RingSizeT numWritten;
 
     *errorCode = 0;
 
-    /* avoid blocking if pipe-thread exited */
-    timeout = (infoPtr->flags & CONSOLE_ASYNC) || !TclPipeThreadIsAlive(&threadInfo->TI)
-	|| TclInExit() || TclInThreadExit() ? 0 : INFINITE;
-    if (WaitForSingleObject(threadInfo->readyEvent, timeout) == WAIT_TIMEOUT) {
-	/*
-	 * The writer thread is blocked waiting for a write to complete and
-	 * the channel is in non-blocking mode.
-	 */
-
-	errno = EWOULDBLOCK;
-	goto error;
-    }
-
-    /*
-     * Check for a background error on the last write.
-     */
-
-    if (infoPtr->writeError) {
-	Tcl_WinConvertError(infoPtr->writeError);
-	infoPtr->writeError = 0;
-	goto error;
+    AcquireSRWLockShared(&gConsoleLock);
+    handleInfoPtr = FindConsoleInfo(chanInfoPtr);
+    if (handleInfoPtr == NULL) {
+	/* Really shouldn't happen since channel is holding a reference */
+	*errorCode = EPIPE;
+	ReleaseSRWLockShared(&gConsoleLock);
+	return -1;
     }
-
-    if (infoPtr->flags & CONSOLE_ASYNC) {
-	/*
-	 * The console is non-blocking, so copy the data into the output
-	 * buffer and restart the writer thread.
-	 */
-
-	if (toWrite > infoPtr->writeBufLen) {
+    AcquireSRWLockExclusive(&handleInfoPtr->lock);
+    ReleaseSRWLockShared(&gConsoleLock); /* AFTER acquiring handleInfoPtr->lock */
+
+    numWritten = RingBufferIn(&handleInfoPtr->buffer, buf, toWrite, 1);
+    while (numWritten < toWrite) {
+	if (handleInfoPtr->lastError != 0) {
+	    Tcl_WinConvertError(handleInfoPtr->lastError);
+	    *errorCode = Tcl_GetErrno();
+	    numWritten = -1;
+	    break;
+	}
+	if (handleInfoPtr->console == NULL) {
+	    *errorCode = EPIPE;
+	    numWritten = -1;
+	    break;
+	}
+	if (chanInfoPtr->flags & CONSOLE_ASYNC) {
+	    /* Async, just accept whatever was written */
+	    break;
+	}
+	else {
 	    /*
-	     * Reallocate the buffer to be large enough to hold the data.
+	     * Release the lock and sleep. Note that because the channel
+	     * holds a reference count on handleInfoPtr, it will not
+	     * be deallocated while the lock is released.
 	     */
-
-	    if (infoPtr->writeBuf) {
-		ckfree(infoPtr->writeBuf);
+	    WakeConditionVariable(&handleInfoPtr->consoleThreadCV);
+	    if (SleepConditionVariableSRW(&handleInfoPtr->interpThreadCV,
+					  &handleInfoPtr->lock,
+					  INFINITE,
+					  0)) {
+		/* Lock is reacquired. Continue loop */
+		numWritten += RingBufferIn(&handleInfoPtr->buffer,
+					   numWritten + buf,
+					   toWrite - numWritten,
+					   1);
+	    }
+	    else {
+		/* Report the error */
+		Tcl_WinConvertError(GetLastError());
+		*errorCode = Tcl_GetErrno();
+		numWritten = -1;
+		break;
 	    }
-	    infoPtr->writeBufLen = toWrite;
-	    infoPtr->writeBuf = (char *)ckalloc(toWrite);
-	}
-	memcpy(infoPtr->writeBuf, buf, toWrite);
-	infoPtr->toWrite = toWrite;
-	ResetEvent(threadInfo->readyEvent);
-	TclPipeThreadSignal(&threadInfo->TI);
-	bytesWritten = toWrite;
-    } else {
-	/*
-	 * In the blocking case, just try to write the buffer directly. This
-	 * avoids an unnecessary copy.
-	 */
-
-	if (WriteConsoleBytes(infoPtr->handle, buf, (DWORD) toWrite,
-		&bytesWritten) == FALSE) {
-	    Tcl_WinConvertError(GetLastError());
-	    goto error;
 	}
     }
-    return bytesWritten;
 
-  error:
-    *errorCode = errno;
-    return -1;
+    ReleaseSRWLockExclusive(&handleInfoPtr->lock);
+    WakeConditionVariable(&handleInfoPtr->consoleThreadCV);
+    return numWritten;
 }
 
 /*
@@ -846,66 +1220,69 @@ ConsoleEventProc(
 				 * such as TCL_FILE_EVENTS. */
 {
     ConsoleEvent *consoleEvPtr = (ConsoleEvent *) evPtr;
-    ConsoleInfo *infoPtr;
-    int mask;
-    ThreadSpecificData *tsdPtr = TCL_TSD_INIT(&dataKey);
+    ConsoleChannelInfo *chanInfoPtr;
+    int freeChannel;
 
     if (!(flags & TCL_FILE_EVENTS)) {
 	return 0;
     }
 
+    chanInfoPtr = consoleEvPtr->chanInfoPtr;
     /*
-     * Search through the list of watched consoles for the one whose handle
-     * matches the event. We do this rather than simply dereferencing the
-     * handle in the event so that consoles can be deleted while the event is
-     * in the queue.
-     */
-
-    for (infoPtr = tsdPtr->firstConsolePtr; infoPtr != NULL;
-	    infoPtr = infoPtr->nextPtr) {
-	if (consoleEvPtr->infoPtr == infoPtr) {
-	    infoPtr->flags &= ~CONSOLE_PENDING;
-	    break;
-	}
-    }
-
-    /*
-     * Remove stale events.
+     * We know chanInfoPtr is valid because its reference count would have
+     * been incremented when the event was queued. The corresponding release
+     * happens in this function.
      */
 
-    if (!infoPtr) {
-	return 1;
-    }
+    AcquireSRWLockShared(&gConsoleLock);
+    chanInfoPtr->flags &= ~CONSOLE_EVENT_QUEUED;
 
     /*
-     * Check to see if the console is readable. Note that we can't tell if a
-     * console is writable, so we always report it as being writable unless we
-     * have detected EOF.
+     * Only handle the event if the Tcl channel has not gone away AND is
+     * still owned by this thread AND is still watching events.
      */
-
-    mask = 0;
-    if (infoPtr->watchMask & TCL_WRITABLE) {
-	if (WaitForSingleObject(infoPtr->writer.readyEvent,
-		0) != WAIT_TIMEOUT) {
-	    mask = TCL_WRITABLE;
+    if (chanInfoPtr->channel && chanInfoPtr->threadId == Tcl_GetCurrentThread()
+	&& (chanInfoPtr->watchMask & (TCL_READABLE|TCL_WRITABLE))) {
+	ConsoleHandleInfo *handleInfoPtr;
+	int mask = 0;
+	handleInfoPtr = FindConsoleInfo(chanInfoPtr);
+	if (handleInfoPtr == NULL) {
+	    /* Console was closed. EOF->read event only (not write) */
+	    if (chanInfoPtr->watchMask & TCL_READABLE) {
+		mask = TCL_READABLE;
+	    }
 	}
-    }
-
-    if (infoPtr->watchMask & TCL_READABLE) {
-	if (WaitForRead(infoPtr, 0) >= 0) {
-	    if (infoPtr->readFlags & CONSOLE_EOF) {
+	else {
+	    AcquireSRWLockShared(&handleInfoPtr->lock);
+	    if (chanInfoPtr->watchMask & TCL_READABLE
+		&& RingBufferLength(&handleInfoPtr->buffer)) {
 		mask = TCL_READABLE;
-	    } else {
-		mask |= TCL_READABLE;
 	    }
+	    else if (RingBufferFreeSpace(&handleInfoPtr->buffer)) {
+		/* Generate write event space available */
+		mask = TCL_WRITABLE;
+	    }
+	    ReleaseSRWLockShared(&handleInfoPtr->lock);
+	}
+	if (mask) {
+	    Tcl_NotifyChannel(chanInfoPtr->channel, mask);
 	}
     }
+    /* Remove the reference to the channel from event record */
+    if (chanInfoPtr->numRefs > 1) {
+	chanInfoPtr->numRefs -= 1;
+	freeChannel = 0;
+    }
+    else {
+	assert(chanInfoPtr->channel == NULL);
+	freeChannel = 1;
+	ckfree(chanInfoPtr);
+    }
+    ReleaseSRWLockShared(&gConsoleLock);
 
-    /*
-     * Inform the channel of the events.
-     */
+    if (freeChannel)
+	ckfree(chanInfoPtr);
 
-    Tcl_NotifyChannel(infoPtr->channel, infoPtr->watchMask & mask);
     return 1;
 }
 
@@ -928,39 +1305,39 @@ ConsoleEventProc(
 static void
 ConsoleWatchProc(
     ClientData instanceData,	/* Console state. */
-    int mask)			/* What events to watch for, OR-ed combination
+    int permissions)		/* What events to watch for, OR-ed combination
 				 * of TCL_READABLE, TCL_WRITABLE and
 				 * TCL_EXCEPTION. */
 {
-    ConsoleInfo **nextPtrPtr, *ptr;
-    ConsoleInfo *infoPtr = (ConsoleInfo *)instanceData;
-    int oldMask = infoPtr->watchMask;
-    ThreadSpecificData *tsdPtr = TCL_TSD_INIT(&dataKey);
+    ConsoleChannelInfo **nextPtrPtr, *ptr;
+    ConsoleChannelInfo *chanInfoPtr = (ConsoleChannelInfo *)instanceData;
+    int oldMask = chanInfoPtr->watchMask;
 
     /*
      * Since most of the work is handled by the background threads, we just
      * need to update the watchMask and then force the notifier to poll once.
      */
 
-    infoPtr->watchMask = mask & infoPtr->validMask;
-    if (infoPtr->watchMask) {
+    chanInfoPtr->watchMask = permissions & chanInfoPtr->permissions;
+    if (chanInfoPtr->watchMask) {
 	Tcl_Time blockTime = { 0, 0 };
 
 	if (!oldMask) {
-	    infoPtr->nextPtr = tsdPtr->firstConsolePtr;
-	    tsdPtr->firstConsolePtr = infoPtr;
+	    /* Add to list of watched channels */
+	    AcquireSRWLockExclusive(&gConsoleLock);
+	    chanInfoPtr->nextWatchingChannelPtr = gWatchingChannelList;
+	    gWatchingChannelList = chanInfoPtr;
+	    ReleaseSRWLockExclusive(&gConsoleLock);
 	}
 	Tcl_SetMaxBlockTime(&blockTime);
     } else if (oldMask) {
-	/*
-	 * Remove the console from the list of watched consoles.
-	 */
+	/* Remove from list of watched channels */
 
-	for (nextPtrPtr = &(tsdPtr->firstConsolePtr), ptr = *nextPtrPtr;
+	for (nextPtrPtr = &gWatchingChannelList, ptr = *nextPtrPtr;
 		ptr != NULL;
-		nextPtrPtr = &ptr->nextPtr, ptr = *nextPtrPtr) {
-	    if (infoPtr == ptr) {
-		*nextPtrPtr = ptr->nextPtr;
+		nextPtrPtr = &ptr->nextWatchingChannelPtr, ptr = *nextPtrPtr) {
+	    if (chanInfoPtr == ptr) {
+		*nextPtrPtr = ptr->nextWatchingChannelPtr;
 		break;
 	    }
 	}
@@ -991,12 +1368,13 @@ ConsoleGetHandleProc(
     TCL_UNUSED(int) /*direction*/,
     ClientData *handlePtr)	/* Where to store the handle. */
 {
-    ConsoleInfo *infoPtr = (ConsoleInfo *)instanceData;
+    ConsoleChannelInfo *chanInfoPtr = (ConsoleChannelInfo *)instanceData;
 
-    *handlePtr = infoPtr->handle;
+    *handlePtr = chanInfoPtr->handle;
     return TCL_OK;
 }
 
+#ifdef OBSOLETE
 /*
  *----------------------------------------------------------------------
  *
@@ -1020,7 +1398,7 @@ ConsoleGetHandleProc(
 
 static int
 WaitForRead(
-    ConsoleInfo *infoPtr,	/* Console state. */
+    ConsoleChannelInfo *infoPtr,	/* Console state. */
     int blocking)		/* Indicates whether call should be blocking
 				 * or not. */
 {
@@ -1100,6 +1478,7 @@ WaitForRead(
 	TclPipeThreadSignal(&threadInfo->TI);
     }
 }
+#endif
 
 /*
  *----------------------------------------------------------------------
@@ -1110,12 +1489,10 @@ WaitForRead(
  *	available on a console.
  *
  * Results:
- *	None.
+ *	Always 0.
  *
  * Side effects:
- *	Signals the main thread when input become available. May cause the
- *	main thread to wake up by posting a message. May one line from the
- *	console for each wait operation.
+ *	Signals the main thread when input become available.
  *
  *----------------------------------------------------------------------
  */
@@ -1124,76 +1501,147 @@ static DWORD WINAPI
 ConsoleReaderThread(
     LPVOID arg)
 {
-    TclPipeThreadInfo *pipeTI = (TclPipeThreadInfo *)arg;
-    ConsoleInfo *infoPtr = NULL; /* access info only after success init/wait */
-    HANDLE *handle = NULL;
-    ConsoleThreadInfo *threadInfo = NULL;
-    int done = 0;
+    ConsoleHandleInfo *handleInfoPtr = (ConsoleHandleInfo *) arg;
+    ConsoleHandleInfo **iterator;
+    BOOL success;
+    char inputChars[200]; /* Temporary buffer */
+    RingSizeT inputLen = 0;
+    RingSizeT inputOffset = 0;
 
-    while (!done) {
-	/*
-	 * Wait for the main thread to signal before attempting to read.
-	 */
+    /*
+     * Keep looping until one of the following happens.
+     *
+     * - there are not more channels listening on the console
+     * - the console handle has been closed
+     *
+     * On each iteration,
+     * - if the channel buffer is full, wait for some channel reader to read
+     * - if there is data in our input buffer copy it to the channel buffer
+     * - get more data from the console
+     */
+
+    /* This thread is holding a reference so pointer is safe */
+    AcquireSRWLockExclusive(&handleInfoPtr->lock);
 
-	if (!TclPipeThreadWaitForSignal(&pipeTI)) {
-	    /* exit */
+    while (1) {
+
+	if (handleInfoPtr->numRefs == 1) {
+	    /* Sole reference. That's this thread. Exit since no one clients */
 	    break;
 	}
-	if (!infoPtr) {
-	    infoPtr = (ConsoleInfo *)pipeTI->clientData;
-	    handle = (HANDLE *)infoPtr->handle;
-	    threadInfo = &infoPtr->reader;
-	}
 
+	if (RingBufferFreeSpace(&handleInfoPtr->buffer) == 0) {
+	    /* No room in buffer. Awaken any reader channels */
+	    WakeConditionVariable(&handleInfoPtr->interpThreadCV);
+		/* XXX - does not wake up fileevent channels! */
+
+	    /* Release lock and wait for room */
+	    success = SleepConditionVariableSRW(&handleInfoPtr->consoleThreadCV,
+						&handleInfoPtr->lock,
+						INFINITE,
+						0);
+	    /* Note: lock has been acquired again! */
+
+	    if (!success && GetLastError() != ERROR_TIMEOUT) {
+		/* TODO - what can be done? Should not happen */
+		/* For now keep going */
+	    }
+	    continue; /* Restart loop so we can check for exit conditions */
+	}
 
 	/*
-	 * Look for data on the console, but first ignore any events that are
-	 * not KEY_EVENTs.
+	 * The shared buffer now has room. If we had any leftover from last
+	 * read, store that.
 	 */
+	if (inputLen > 0) {
+	    RingSizeT nStored;
+	    HANDLE consoleHandle;
+	    ConsoleChannelInfo *chanInfoPtr;
+
+	    nStored = RingBufferIn(&handleInfoPtr->buffer,
+				   inputOffset + inputChars,
+				   inputLen - inputOffset,
+				   1);
+	    inputOffset += nStored;
+	    if (inputOffset == inputLen) {
+		/* Temp buffer now empty */
+		inputOffset = 0;
+		inputLen = 0;
+	    }
+	    /* Wake up any threads waiting synchronously. */
+	    WakeConditionVariable(&handleInfoPtr->interpThreadCV);
 
-	if (ReadConsoleBytes(handle, infoPtr->buffer, CONSOLE_BUFFER_SIZE,
-		(LPDWORD) &infoPtr->bytesRead) != FALSE) {
 	    /*
-	     * Data was stored in the buffer.
+	     * Wake up all channels registered for file events. Note in
+	     * order to follow the locking hierarchy, we need to release
+	     * handleInfoPtr->lock before acquiring gConsoleLock and
+	     * relock it.
 	     */
-
-	    infoPtr->readFlags |= CONSOLE_BUFFERED;
-	} else {
-	    DWORD err = GetLastError();
-
-	    if (err == (DWORD) EOF) {
-		infoPtr->readFlags = CONSOLE_EOF;
+	    consoleHandle = handleInfoPtr->console;
+	    ReleaseSRWLockExclusive(&handleInfoPtr->lock);
+	    AcquireSRWLockShared(&gConsoleLock); /* Shared-read lock */
+	    for (chanInfoPtr = gWatchingChannelList; chanInfoPtr;
+		 chanInfoPtr = chanInfoPtr->nextWatchingChannelPtr) {
+		/*
+		 * Notify channels interested in our handle AND that have
+		 * a thread attached.
+		 * No lock needed for chanInfoPtr. See ConsoleChannelInfo.
+		 */
+		if (chanInfoPtr->handle == consoleHandle
+		    && chanInfoPtr->threadId != NULL) {
+		    Tcl_ThreadAlert(chanInfoPtr->threadId);
+		}
 	    }
-	    done = 1;
+	    ReleaseSRWLockShared(&gConsoleLock);
+	    AcquireSRWLockExclusive(&handleInfoPtr->lock);
+	    continue; /* Restart loop */
 	}
 
 	/*
-	 * Signal the main thread by signalling the readable event and then
-	 * waking up the notifier thread.
+	 * Need to go get more data from console. We only store the last
+	 * error. It is up to channel handlers to decide whether to close or
+	 * what to do.
 	 */
+	ReleaseSRWLockExclusive(&handleInfoPtr->lock);
+	handleInfoPtr->lastError =
+	    ReadConsoleChars(handleInfoPtr->console,
+			     (WCHAR *)inputChars,
+			     sizeof(inputChars) / sizeof(WCHAR),
+			     &inputLen);
+	inputLen *= sizeof(WCHAR);
+	AcquireSRWLockExclusive(&handleInfoPtr->lock);
+    }
 
-	SetEvent(threadInfo->readyEvent);
-
-	/*
-	 * Alert the foreground thread. Note that we need to treat this like a
-	 * critical section so the foreground thread does not terminate this
-	 * thread while we are holding a mutex in the notifier code.
-	 */
+    /*
+     * Exiting:
+     * - remove the console from global list
+     * - close the handle if still valid
+     * - release the structure
+     */
+    ReleaseSRWLockExclusive(&handleInfoPtr->lock);
+    AcquireSRWLockExclusive(&gConsoleLock); /* Modifying - exclusive lock */
+    for (iterator = &gConsoleHandleInfoList; *iterator;
+	 iterator = &(*iterator)->nextPtr) {
+	if (*iterator == handleInfoPtr) {
+	    *iterator = handleInfoPtr->nextPtr;
+	    break;
+	}
+    }
+    ReleaseSRWLockExclusive(&gConsoleLock);
 
-	Tcl_MutexLock(&consoleMutex);
-	if (infoPtr->threadId != NULL) {
-	    /*
-	     * TIP #218. When in flight ignore the event, no one will receive
-	     * it anyway.
-	     */
+    /* No need for relocking - no other thread should have access to it now */
+    RingBufferClear(&handleInfoPtr->buffer);
 
-	    Tcl_ThreadAlert(infoPtr->threadId);
-	}
-	Tcl_MutexUnlock(&consoleMutex);
+    if (handleInfoPtr->console) {
+	SetConsoleMode(handleInfoPtr->console, handleInfoPtr->initMode);
     }
+    /*
+     * NOTE: we do not call CloseHandle(handleInfoPtr->console)
+     * As per the GetStdHandle documentation, it need not be closed.
+     * TODO - what about when application closes and re-opens? - Test
+     */
 
-    /* Worker exit, so inform the main thread or free TI-structure (if owned) */
-    TclPipeThreadExit(&pipeTI);
+    ckfree(handleInfoPtr);
 
     return 0;
 }
@@ -1210,89 +1658,262 @@ ConsoleReaderThread(
  *	Always returns 0.
  *
  * Side effects:
-
- *	Signals the main thread when an output operation is completed. May
- *	cause the main thread to wake up by posting a message.
+ *	Signals the main thread when an output operation is completed.
  *
  *----------------------------------------------------------------------
  */
-
 static DWORD WINAPI
-ConsoleWriterThread(
-    LPVOID arg)
+ConsoleWriterThread(LPVOID arg)
 {
-    TclPipeThreadInfo *pipeTI = (TclPipeThreadInfo *)arg;
-    ConsoleInfo *infoPtr = NULL; /* access info only after success init/wait */
-    HANDLE *handle = NULL;
-    ConsoleThreadInfo *threadInfo = NULL;
-    DWORD count, toWrite;
-    char *buf;
-    int done = 0;
-
-    while (!done) {
-	/*
-	 * Wait for the main thread to signal before attempting to write.
-	 */
-	if (!TclPipeThreadWaitForSignal(&pipeTI)) {
-	    /* exit */
-	    break;
-	}
-	if (!infoPtr) {
-	    infoPtr = (ConsoleInfo *)pipeTI->clientData;
-	    handle = (HANDLE *)infoPtr->handle;
-	    threadInfo = &infoPtr->writer;
-	}
+    ConsoleHandleInfo *handleInfoPtr = (ConsoleHandleInfo *) arg;
+    ConsoleHandleInfo **iterator;
+    ConsoleChannelInfo *chanInfoPtr = NULL;
+    BOOL success;
+    char buffer[4000];
+    RingSizeT length;
+
+    /*
+     * Keep looping until one of the following happens.
+     *
+     * - there are not more channels listening on the console
+     * - the console handle has been closed
+     *
+     * On each iteration,
+     * - if the channel buffer is empty, wait for some channel writer to write
+     * - if there is data in our buffer, write it to the console
+     */
 
-	buf = infoPtr->writeBuf;
-	toWrite = infoPtr->toWrite;
+    /* This thread is holding a reference so pointer is safe */
+    AcquireSRWLockExclusive(&handleInfoPtr->lock);
+    while (1) {
+	/* handleInfoPtr->lock must be held on entry to loop */
+
+	int offset;
+	HANDLE consoleHandle;
 
 	/*
-	 * Loop until all of the bytes are written or an error occurs.
+	 * Sadly, we need to do another copy because do not want to hold
+	 * a lock on handleInfoPtr->buffer while calling WriteConsole as that
+	 * might block. Also, we only want to copy an integral number of
+	 * WCHAR's, i.e. even number of chars so do some length checks up
+	 * front.
 	 */
-
-	while (toWrite > 0) {
-	    if (WriteConsoleBytes(handle, buf, (DWORD) toWrite,
-		    &count) == FALSE) {
-		infoPtr->writeError = GetLastError();
-		done = 1;
+	length = RingBufferLength(&handleInfoPtr->buffer);
+	length &= ~1; /* Copy integral number of WCHARs -> even number of bytes */
+	if (length == 0) {
+	    /* No data to write */
+	    if (handleInfoPtr->numRefs == 1) {
+		/*
+		 * Sole reference. That's this thread. Exit since no clients
+		 * and no buffered output.
+		 */
 		break;
 	    }
-	    toWrite -= count;
-	    buf += count;
+	    /* Wake up any threads waiting synchronously. */
+	    WakeConditionVariable(&handleInfoPtr->interpThreadCV);
+	    success = SleepConditionVariableSRW(&handleInfoPtr->consoleThreadCV,
+						&handleInfoPtr->lock,
+						INFINITE,
+						0);
+	    /* Note: lock has been acquired again! */
+	    if (!success && GetLastError() != ERROR_TIMEOUT) {
+		/* TODO - what can be done? Should not happen */
+		/* For now keep going */
+	    }
+	    continue;
 	}
 
-	/*
-	 * Signal the main thread by signalling the writable event and then
-	 * waking up the notifier thread.
-	 */
-
-	SetEvent(threadInfo->readyEvent);
+	/* We have data to write */
+	if (length > (sizeof(buffer) / sizeof(buffer[0]))) {
+	    length = sizeof(buffer);
+	}
+	/* No need to check result, we already checked length bytes available */
+	RingBufferOut(&handleInfoPtr->buffer, buffer, length, 0);
+
+	WakeConditionVariable(&handleInfoPtr->interpThreadCV);
+	ReleaseSRWLockExclusive(&handleInfoPtr->lock);
+	offset = 0;
+	while (length > 0) {
+	    RingSizeT numWChars = length / sizeof(WCHAR);
+	    DWORD status;
+	    status = WriteConsoleChars(
+		handleInfoPtr->console, (WCHAR *) (offset + buffer) , numWChars, &numWChars);
+	    if (status != 0) {
+		/* Only overwrite if no previous error */
+		if (handleInfoPtr->lastError == 0) {
+		    handleInfoPtr->lastError = status;
+		}
+		/* Assume this write is done but keep looping in case
+		 * it is a transient error. Not sure just closing handle
+		 * and exiting thread is a good idea.
+		 */
+		break;
+	    }
+	    length -= numWChars * sizeof(WCHAR);
+	    offset += numWChars * sizeof(WCHAR);
+	}
 
 	/*
-	 * Alert the foreground thread. Note that we need to treat this like a
-	 * critical section so the foreground thread does not terminate this
-	 * thread while we are holding a mutex in the notifier code.
+	 * Wake up all channels registered for file events. Note in
+	 * order to follow the locking hierarchy, we need to release
+	 * handleInfoPtr->lock before acquiring gConsoleLock and
+	 * relock it.
 	 */
-
-	Tcl_MutexLock(&consoleMutex);
-	if (infoPtr->threadId != NULL) {
+	/* Wake up any threads waiting synchronously. */
+	WakeConditionVariable(&handleInfoPtr->interpThreadCV);
+	AcquireSRWLockShared(&gConsoleLock); /* Shared-read lock */
+	consoleHandle = handleInfoPtr->console;
+	for (chanInfoPtr = gWatchingChannelList; chanInfoPtr;
+	     chanInfoPtr = chanInfoPtr->nextWatchingChannelPtr) {
 	    /*
-	     * TIP #218. When in flight ignore the event, no one will receive
-	     * it anyway.
+	     * Notify channels interested in our handle AND that have
+	     * a thread attached.
+	     * No lock needed for chanInfoPtr. See ConsoleChannelInfo.
 	     */
+	    if (chanInfoPtr->handle == consoleHandle
+		&& chanInfoPtr->threadId != NULL) {
+		Tcl_ThreadAlert(chanInfoPtr->threadId);
+	    }
+	}
+	ReleaseSRWLockShared(&gConsoleLock);
+	AcquireSRWLockExclusive(&handleInfoPtr->lock);
+    }
 
-	    Tcl_ThreadAlert(infoPtr->threadId);
+    /*
+     * Exiting:
+     * - remove the console from global list
+     * - close the handle if still valid
+     * - release the structure
+     */
+    ReleaseSRWLockExclusive(&handleInfoPtr->lock);
+    AcquireSRWLockExclusive(&gConsoleLock); /* Modifying - exclusive lock */
+    for (iterator = &gConsoleHandleInfoList; *iterator;
+	 iterator = &(*iterator)->nextPtr) {
+	if (*iterator == handleInfoPtr) {
+	    *iterator = handleInfoPtr->nextPtr;
+	    break;
 	}
-	Tcl_MutexUnlock(&consoleMutex);
     }
+    ReleaseSRWLockExclusive(&gConsoleLock);
+
+    RingBufferClear(&handleInfoPtr->buffer);
+
+    /*
+     * NOTE: we do not call CloseHandle(handleInfoPtr->console)
+     * As per the GetStdHandle documentation, it need not be closed.
+     * TODO - what about when application closes and re-opens? - Test
+     */
 
-    /* Worker exit, so inform the main thread or free TI-structure (if owned) */
-    TclPipeThreadExit(&pipeTI);
+    ckfree(handleInfoPtr);
 
     return 0;
 }
 
 /*
+ *------------------------------------------------------------------------
+ *
+ * AllocateConsoleHandleInfo --
+ *
+ *    Allocates a ConsoleHandleInfo for the passed console handle. As
+ *    a side effect starts a console thread to handle i/o on the handle.
+ *
+ *    Important: Caller must be holding an EXCLUSIVE lock on gConsoleLock
+ *    when calling this function. The lock continues to be held on return.
+ *
+ * Results:
+ *    Pointer to an unlocked ConsoleHandleInfo structure. The reference
+ *    count on the structure is 1. This corresponds to the common reference
+ *    from the console thread and the gConsoleHandleInfoList. Returns NULL
+ *    on error.
+ *
+ * Side effects:
+ *    A console reader or writer thread is started. The returned structure
+ *    is placed on the active console handler list gConsoleHandleInfoList.
+ *
+ *------------------------------------------------------------------------
+ */
+static ConsoleHandleInfo *
+AllocateConsoleHandleInfo(
+    HANDLE consoleHandle,
+    int permissions)   /* TCL_READABLE or TCL_WRITABLE */
+{
+    ConsoleHandleInfo *handleInfoPtr;
+    DWORD consoleMode;
+
+
+    handleInfoPtr = (ConsoleHandleInfo *)ckalloc(sizeof(*handleInfoPtr));
+    handleInfoPtr->console = consoleHandle;
+    InitializeSRWLock(&handleInfoPtr->lock);
+    InitializeConditionVariable(&handleInfoPtr->consoleThreadCV);
+    InitializeConditionVariable(&handleInfoPtr->interpThreadCV);
+    RingBufferInit(&handleInfoPtr->buffer, CONSOLE_BUFFER_SIZE);
+    handleInfoPtr->lastError = 0;
+    handleInfoPtr->permissions = permissions;
+    handleInfoPtr->numRefs = 1; /* See function header */
+    if (permissions == TCL_READABLE) {
+	GetConsoleMode(consoleHandle, &handleInfoPtr->initMode);
+	consoleMode = handleInfoPtr->initMode;
+	consoleMode &= ~(ENABLE_WINDOW_INPUT | ENABLE_MOUSE_INPUT);
+	consoleMode |= ENABLE_LINE_INPUT;
+	SetConsoleMode(consoleHandle, consoleMode);
+    }
+    handleInfoPtr->consoleThread = CreateThread(
+	NULL, /* default security descriptor */
+	8192, /* Stack size - will get rounded up to allocation granularity */
+	permissions == TCL_READABLE ? ConsoleReaderThread : ConsoleWriterThread,
+	handleInfoPtr, /* Pass to thread */
+	0,             /* Flags - no special cases */
+	NULL);         /* Don't care about thread id */
+    if (handleInfoPtr->consoleThread == NULL) {
+	/* Note - SRWLock and condition variables do not need finalization */
+	RingBufferClear(&handleInfoPtr->buffer);
+	ckfree(handleInfoPtr);
+	return NULL;
+    }
+
+    /* Chain onto global list */
+    handleInfoPtr->nextPtr = gConsoleHandleInfoList;
+    gConsoleHandleInfoList = handleInfoPtr;
+
+    return handleInfoPtr;
+}
+
+/*
+ *------------------------------------------------------------------------
+ *
+ * FindConsoleInfo --
+ *
+ *    Finds the ConsoleHandleInfo record for a given ConsoleChannelInfo.
+ *    The found record must match the console handle. It is the caller's
+ *    responsibility to check the permissions (read/write) in the returned
+ *    ConsoleHandleInfo match permissions in chanInfoPtr. This function does
+ *    not check that.
+ *
+ *    Important: Caller must be holding an shared or exclusive lock on
+ *    gConsoleMutex. That ensures the returned pointer stays valid on
+ *    return without risk of deallocation by other threads.
+ *
+ * Results:
+ *    Pointer to the found ConsoleHandleInfo or NULL if not found
+ *
+ * Side effects:
+ *    None.
+ *
+ *------------------------------------------------------------------------
+ */
+static ConsoleHandleInfo *
+FindConsoleInfo(const ConsoleChannelInfo *chanInfoPtr)
+{
+    ConsoleHandleInfo *handleInfoPtr;
+    for (handleInfoPtr = gConsoleHandleInfoList; handleInfoPtr; handleInfoPtr = handleInfoPtr->nextPtr) {
+	if (handleInfoPtr->console == chanInfoPtr->handle) {
+	    return handleInfoPtr;
+	}
+    }
+    return NULL;
+}
+
+/*
  *----------------------------------------------------------------------
  *
  * TclWinOpenConsoleChannel --
@@ -1309,33 +1930,30 @@ ConsoleWriterThread(
  *
  *----------------------------------------------------------------------
  */
-
 Tcl_Channel
 TclWinOpenConsoleChannel(
     HANDLE handle,
     char *channelName,
     int permissions)
 {
-    char encoding[4 + TCL_INTEGER_SPACE];
-    ConsoleInfo *infoPtr;
-    DWORD modes;
+    ConsoleChannelInfo *chanInfoPtr;
+    ConsoleHandleInfo *handleInfoPtr;
 
-    ConsoleInit();
-
-    /*
-     * See if a channel with this handle already exists.
-     */
+    /* A console handle can either be input or output, not both */
+    if (permissions != TCL_READABLE && permissions != TCL_WRITABLE) {
+	return NULL;
+    }
 
-    infoPtr = (ConsoleInfo *)ckalloc(sizeof(ConsoleInfo));
-    memset(infoPtr, 0, sizeof(ConsoleInfo));
+    ConsoleInit();
 
-    infoPtr->validMask = permissions;
-    infoPtr->handle = handle;
-    infoPtr->channel = (Tcl_Channel) NULL;
+    chanInfoPtr = (ConsoleChannelInfo *)ckalloc(sizeof(*chanInfoPtr));
+    memset(chanInfoPtr, 0, sizeof(*chanInfoPtr));
 
-    wsprintfA(encoding, "cp%d", GetConsoleCP());
+    chanInfoPtr->permissions = permissions;
+    chanInfoPtr->handle = handle;
+    chanInfoPtr->channel = (Tcl_Channel) NULL;
 
-    infoPtr->threadId = Tcl_GetCurrentThread();
+    chanInfoPtr->threadId = Tcl_GetCurrentThread();
 
     /*
      * Use the pointer for the name of the result channel. This keeps the
@@ -1343,10 +1961,7 @@ TclWinOpenConsoleChannel(
      * for instance).
      */
 
-    sprintf(channelName, "file%" TCL_Z_MODIFIER "x", (size_t) infoPtr);
-
-    infoPtr->channel = Tcl_CreateChannel(&consoleChannelType, channelName,
-	    infoPtr, permissions);
+    sprintf(channelName, "file%" TCL_Z_MODIFIER "x", (size_t) chanInfoPtr);
 
     if (permissions & TCL_READABLE) {
 	/*
@@ -1355,38 +1970,78 @@ TclWinOpenConsoleChannel(
 	 * we only want to catch when complete lines are ready for reading.
 	 */
 
-	infoPtr->flags |= CONSOLE_READ_OPS;
-	GetConsoleMode(infoPtr->handle, &infoPtr->initMode);
-	modes = infoPtr->initMode;
-	modes &= ~(ENABLE_WINDOW_INPUT | ENABLE_MOUSE_INPUT);
-	modes |= ENABLE_LINE_INPUT;
-	SetConsoleMode(infoPtr->handle, modes);
-
-	infoPtr->reader.readyEvent = CreateEventW(NULL, TRUE, TRUE, NULL);
-	infoPtr->reader.thread = CreateThread(NULL, 256, ConsoleReaderThread,
-		TclPipeThreadCreateTI(&infoPtr->reader.TI, infoPtr,
-			infoPtr->reader.readyEvent), 0, NULL);
+	chanInfoPtr->flags |= CONSOLE_READ_OPS;
+	GetConsoleMode(handle, &chanInfoPtr->initMode);
+
+#ifdef OBSOLETE
+	/* Why was priority being set on console input? Code smell */
 	SetThreadPriority(infoPtr->reader.thread, THREAD_PRIORITY_HIGHEST);
+#endif
+    }
+    else {
+	/* Already checked permissions is WRITABLE if not READABLE */
+	/* TODO - enable ansi escape processing? */
     }
 
-    if (permissions & TCL_WRITABLE) {
+    /*
+     * Global lock but that's ok. See comments top of file. Allocations
+     * will happen only a few times in the life of a process and that too
+     * generally at start up where only one thread is active.
+     */
+    AcquireSRWLockExclusive(&gConsoleLock); /*Allocate needs exclusive lock */
 
-	infoPtr->writer.readyEvent = CreateEventW(NULL, TRUE, TRUE, NULL);
-	infoPtr->writer.thread = CreateThread(NULL, 256, ConsoleWriterThread,
-		TclPipeThreadCreateTI(&infoPtr->writer.TI, infoPtr,
-			infoPtr->writer.readyEvent), 0, NULL);
-	SetThreadPriority(infoPtr->writer.thread, THREAD_PRIORITY_HIGHEST);
+    handleInfoPtr = FindConsoleInfo(chanInfoPtr);
+    if (handleInfoPtr == NULL) {
+	/* Not found. Allocate one */
+	handleInfoPtr = AllocateConsoleHandleInfo(handle, permissions);
+    }
+    else {
+	/* Found. Its direction (read/write) better be the same */
+	if (handleInfoPtr->permissions != permissions) {
+	    handleInfoPtr = NULL;
+	}
+    }
+
+    if (handleInfoPtr == NULL) {
+	ReleaseSRWLockExclusive(&gConsoleLock);
+	if (permissions == TCL_READABLE) {
+	    SetConsoleMode(handle, chanInfoPtr->initMode);
+	}
+	ckfree(chanInfoPtr);
+	return NULL;
     }
 
     /*
+     * There is effectively a reference to this structure from the Tcl
+     * channel subsystem. So record that. This reference will be dropped
+     * when the Tcl channel is closed.
+     */
+    chanInfoPtr->numRefs = 1;
+
+    /*
+     * Need to keep track of number of referencing channels for closing.
+     * The pointer is safe since there is a reference held to it from
+     * gConsoleHandleInfoList but still need to lock the structure itself
+     */
+    AcquireSRWLockExclusive(&handleInfoPtr->lock);
+    handleInfoPtr->numRefs += 1;
+    ReleaseSRWLockExclusive(&handleInfoPtr->lock);
+
+    ReleaseSRWLockExclusive(&gConsoleLock);
+
+    /* Note Tcl_CreateChannel never fails other than panic on error */
+    chanInfoPtr->channel = Tcl_CreateChannel(&consoleChannelType, channelName,
+	    chanInfoPtr, permissions);
+
+    /*
      * Files have default translation of AUTO and ^Z eof char, which means
      * that a ^Z will be accepted as EOF when reading.
      */
 
-    Tcl_SetChannelOption(NULL, infoPtr->channel, "-translation", "auto");
-    Tcl_SetChannelOption(NULL, infoPtr->channel, "-eofchar", "\032 {}");
-    Tcl_SetChannelOption(NULL, infoPtr->channel, "-encoding", "utf-16");
-    return infoPtr->channel;
+    Tcl_SetChannelOption(NULL, chanInfoPtr->channel, "-translation", "auto");
+    Tcl_SetChannelOption(NULL, chanInfoPtr->channel, "-eofchar", "\032 {}");
+    Tcl_SetChannelOption(NULL, chanInfoPtr->channel, "-encoding", "utf-16");
+    return chanInfoPtr->channel;
 }
 
 /*
@@ -1410,33 +2065,16 @@ ConsoleThreadActionProc(
     ClientData instanceData,
     int action)
 {
-    ConsoleInfo *infoPtr = (ConsoleInfo *)instanceData;
-
-    /*
-     * We do not access firstConsolePtr in the thread structures. This is not
-     * for all serials managed by the thread, but only those we are watching.
-     * Removal of the filevent handlers before transfer thus takes care of
-     * this structure.
-     */
+    ConsoleChannelInfo *chanInfoPtr = (ConsoleChannelInfo *)instanceData;
 
-    Tcl_MutexLock(&consoleMutex);
+    /* No need for any locks as no other thread will be writing to it */
     if (action == TCL_CHANNEL_THREAD_INSERT) {
-	/*
-	 * We can't copy the thread information from the channel when the
-	 * channel is created. At this time the channel back pointer has not
-	 * been set yet. However in that case the threadId has already been
-	 * set by TclpCreateCommandChannel itself, so the structure is still
-	 * good.
-	 */
-
-	ConsoleInit();
-	if (infoPtr->channel != NULL) {
-	    infoPtr->threadId = Tcl_GetChannelThread(infoPtr->channel);
-	}
-    } else {
-	infoPtr->threadId = NULL;
+	ConsoleInit(); /* Needed to set up event source handlers for this thread */
+	chanInfoPtr->threadId = Tcl_GetCurrentThread();
+    }
+    else {
+	chanInfoPtr->threadId = NULL;
     }
-    Tcl_MutexUnlock(&consoleMutex);
 }
 
 /*
@@ -1456,7 +2094,6 @@ ConsoleThreadActionProc(
  *
  *----------------------------------------------------------------------
  */
-
 static int
 ConsoleSetOptionProc(
     ClientData instanceData,	/* File state. */
@@ -1464,7 +2101,7 @@ ConsoleSetOptionProc(
     const char *optionName,	/* Which option to set? */
     const char *value)		/* New value for option. */
 {
-    ConsoleInfo *infoPtr = (ConsoleInfo *)instanceData;
+    ConsoleChannelInfo *chanInfoPtr = (ConsoleChannelInfo *)instanceData;
     int len = strlen(optionName);
     int vlen = strlen(value);
 
@@ -1472,11 +2109,11 @@ ConsoleSetOptionProc(
      * Option -inputmode normal|password|raw
      */
 
-    if ((infoPtr->flags & CONSOLE_READ_OPS) && (len > 1) &&
+    if ((chanInfoPtr->flags & CONSOLE_READ_OPS) && (len > 1) &&
 	    (strncmp(optionName, "-inputmode", len) == 0)) {
 	DWORD mode;
 
-	if (GetConsoleMode(infoPtr->handle, &mode) == 0) {
+	if (GetConsoleMode(chanInfoPtr->handle, &mode) == 0) {
 	    Tcl_WinConvertError(GetLastError());
 	    if (interp != NULL) {
 		Tcl_SetObjResult(interp, Tcl_ObjPrintf(
@@ -1496,8 +2133,7 @@ ConsoleSetOptionProc(
 	    /*
 	     * Reset to the initial mode, whatever that is.
 	     */
-
-	    mode = infoPtr->initMode;
+	    mode = chanInfoPtr->initMode;
 	} else {
 	    if (interp) {
 		Tcl_SetObjResult(interp, Tcl_ObjPrintf(
@@ -1508,7 +2144,7 @@ ConsoleSetOptionProc(
 	    }
 	    return TCL_ERROR;
 	}
-	if (SetConsoleMode(infoPtr->handle, mode) == 0) {
+	if (SetConsoleMode(chanInfoPtr->handle, mode) == 0) {
 	    Tcl_WinConvertError(GetLastError());
 	    if (interp != NULL) {
 		Tcl_SetObjResult(interp, Tcl_ObjPrintf(
@@ -1518,19 +2154,10 @@ ConsoleSetOptionProc(
 	    return TCL_ERROR;
 	}
 
-	/*
-	 * If we've changed the mode from default, schedule a reset later.
-	 */
-
-	if (mode == infoPtr->initMode) {
-	    infoPtr->flags &= ~CONSOLE_RESET;
-	} else {
-	    infoPtr->flags |= CONSOLE_RESET;
-	}
 	return TCL_OK;
     }
 
-    if (infoPtr->flags & CONSOLE_READ_OPS) {
+    if (chanInfoPtr->flags & CONSOLE_READ_OPS) {
 	return Tcl_BadChannelOption(interp, optionName, "inputmode");
     } else {
 	return Tcl_BadChannelOption(interp, optionName, "");
@@ -1562,7 +2189,7 @@ ConsoleGetOptionProc(
     const char *optionName,	/* Option to get. */
     Tcl_DString *dsPtr)		/* Where to store value(s). */
 {
-    ConsoleInfo *infoPtr = (ConsoleInfo *)instanceData;
+    ConsoleChannelInfo *chanInfoPtr = (ConsoleChannelInfo *)instanceData;
     int valid = 0;		/* Flag if valid option parsed. */
     unsigned int len;
     char buf[TCL_INTEGER_SPACE];
@@ -1580,7 +2207,7 @@ ConsoleGetOptionProc(
      * represents what almost all scripts really want to know.
      */
 
-    if (infoPtr->flags & CONSOLE_READ_OPS) {
+    if (chanInfoPtr->flags & CONSOLE_READ_OPS) {
 	if (len == 0) {
 	    Tcl_DStringAppendElement(dsPtr, "-inputmode");
 	}
@@ -1588,7 +2215,7 @@ ConsoleGetOptionProc(
 	    DWORD mode;
 
 	    valid = 1;
-	    if (GetConsoleMode(infoPtr->handle, &mode) == 0) {
+	    if (GetConsoleMode(chanInfoPtr->handle, &mode) == 0) {
 		Tcl_WinConvertError(GetLastError());
 		if (interp != NULL) {
 		    Tcl_SetObjResult(interp, Tcl_ObjPrintf(
@@ -1619,7 +2246,7 @@ ConsoleGetOptionProc(
 	CONSOLE_SCREEN_BUFFER_INFO consoleInfo;
 
 	valid = 1;
-	if (!GetConsoleScreenBufferInfo(infoPtr->handle, &consoleInfo)) {
+	if (!GetConsoleScreenBufferInfo(chanInfoPtr->handle, &consoleInfo)) {
 	    Tcl_WinConvertError(GetLastError());
 	    if (interp != NULL) {
 		Tcl_SetObjResult(interp, Tcl_ObjPrintf(
@@ -1639,7 +2266,7 @@ ConsoleGetOptionProc(
     if (valid) {
 	return TCL_OK;
     }
-    if (infoPtr->flags & CONSOLE_READ_OPS) {
+    if (chanInfoPtr->flags & CONSOLE_READ_OPS) {
 	return Tcl_BadChannelOption(interp, optionName, "inputmode winsize");
     } else {
 	return Tcl_BadChannelOption(interp, optionName, "");