path: root/unix/tclKqueueNotfy.c

/*
 * tclKqueueNotfy.c --
 *
 *	This file contains the implementation of the kqueue()-based
 *	DragonFly/Free/Net/OpenBSD-specific notifier, which is the lowest-
 *	level part of the Tcl event loop. This file works together with
 *	generic/tclNotify.c.
 *
 * Copyright (c) 1995-1997 Sun Microsystems, Inc.
 * Copyright (c) 2016 Lucio Andrés Illanes Albornoz <l.illanes@gmx.de>
 *
 * See the file "license.terms" for information on usage and redistribution
 * of this file, and for a DISCLAIMER OF ALL WARRANTIES.
 */

#include "tclInt.h"
#ifndef HAVE_COREFOUNDATION	/* Darwin/Mac OS X CoreFoundation notifier is
				 * in tclMacOSXNotify.c */
#if defined(NOTIFIER_KQUEUE) && TCL_THREADS

#include <signal.h>
#include <sys/types.h>
#include <sys/event.h>
#include <sys/queue.h>
#include <sys/time.h>

/*
 * This structure is used to keep track of the notifier info for a registered
 * file.
 */

struct PlatformEventData;
typedef struct FileHandler {
    int fd;
    int mask;			/* Mask of desired events: TCL_READABLE,
				 * etc. */
    int readyMask;		/* Mask of events that have been seen since
				 * the last time file handlers were invoked
				 * for this file. */
    Tcl_FileProc *proc;		/* Function to call, in the style of
				 * Tcl_CreateFileHandler. */
    ClientData clientData;	/* Argument to pass to proc. */
    struct FileHandler *nextPtr;/* Next in list of all files we care about. */
    LIST_ENTRY(FileHandler) readyNode;
				/* Next/previous in list of FileHandlers asso-
				 * ciated with regular files (S_IFREG) that are
				 * ready for I/O. */
    struct PlatformEventData *pedPtr;
				/* Pointer to PlatformEventData associating this
				 * FileHandler with kevent(2) events. */
} FileHandler;

/*
 * The following structure associates a FileHandler and the thread that owns
 * it with the file descriptors of interest and their event masks passed to
 * kevent(2) and their corresponding event(s) returned by kevent(2).
 */

struct ThreadSpecificData;
struct PlatformEventData {
    FileHandler *filePtr;
    struct ThreadSpecificData *tsdPtr;
};

/*
 * The following structure is what is added to the Tcl event queue when file
 * handlers are ready to fire.
 */

typedef struct {
    Tcl_Event header;		/* Information that is standard for all
				 * events. */
    int fd;			/* File descriptor that is ready. Used to find
				 * the FileHandler structure for the file
				 * (can't point directly to the FileHandler
				 * structure because it could go away while
				 * the event is queued). */
} FileHandlerEvent;

/*
 * The following static structure contains the state information for the
 * kqueue based implementation of the Tcl notifier. One of these structures is
 * created for each thread that is using the notifier.
 */

LIST_HEAD(PlatformReadyFileHandlerList, FileHandler);
typedef struct ThreadSpecificData {
    FileHandler *firstFileHandlerPtr;
				/* Pointer to head of file handler list. */
    struct PlatformReadyFileHandlerList firstReadyFileHandlerPtr;
				/* Pointer to head of list of FileHandlers
				 * associated with regular files (S_IFREG)
				 * that are ready for I/O. */
    pthread_mutex_t notifierMutex;
				/* Mutex protecting notifier termination in
				 * PlatformEventsFinalize. */
    int triggerPipe[2];		/* pipe(2) used by other threads to wake
				 * up this thread for inter-thread IPC. */
    int eventsFd;		/* kqueue(2) file descriptor used to wait for
				 * fds. */
    struct kevent *readyEvents;	/* Pointer to at most maxReadyEvents events
				 * returned by kevent(2). */
    size_t maxReadyEvents;	/* Count of kevents in readyEvents. */
} ThreadSpecificData;

static Tcl_ThreadDataKey dataKey;

/*
 * Forward declarations of internal functions.
 */

static void		PlatformEventsControl(FileHandler *filePtr,
			    ThreadSpecificData *tsdPtr, int op, int isNew);
static void		PlatformEventsFinalize(void);
static void		PlatformEventsInit(void);
static int		PlatformEventsTranslate(struct kevent *eventPtr);
static int		PlatformEventsWait(struct kevent *events,
			    size_t numEvents, struct timeval *timePtr);

#include "tclUnixNotfy.c"

/*
 *----------------------------------------------------------------------
 *
 * Tcl_InitNotifier --
 *
 *	Initializes the platform specific notifier state.
 *
 * Results:
 *	Returns a handle to the notifier state for this thread.
 *
 * Side effects:
 *	If no initNotifierProc notifier hook exists, PlatformEventsInit
 *	is called.
 *
 *----------------------------------------------------------------------
 */

ClientData
Tcl_InitNotifier(void)
{
    if (tclNotifierHooks.initNotifierProc) {
	return tclNotifierHooks.initNotifierProc();
    } else {
	ThreadSpecificData *tsdPtr = TCL_TSD_INIT(&dataKey);

	PlatformEventsInit();
	return tsdPtr;
    }
}

/*
 *----------------------------------------------------------------------
 *
 * Tcl_FinalizeNotifier --
 *
 *	This function is called to cleanup the notifier state before a thread
 *	is terminated.
 *
 * Results:
 *	None.
 *
 * Side effects:
 *	If no finalizeNotifierProc notifier hook exists, PlatformEvents-
 *	Finalize is called.
 *
 *----------------------------------------------------------------------
 */

void
Tcl_FinalizeNotifier(
    ClientData clientData)
{
    if (tclNotifierHooks.finalizeNotifierProc) {
	tclNotifierHooks.finalizeNotifierProc(clientData);
	return;
    } else {
	PlatformEventsFinalize();
    }
}

/*
 *----------------------------------------------------------------------
 *
 * PlatformEventsControl --
 *
 *	This function registers interest for the file descriptor and the mask
 *	of TCL_* bits associated with filePtr on the kqueue file descriptor
 *	associated with tsdPtr.
 *
 *	Future calls to kevent will return filePtr and tsdPtr alongside with
 *	the event registered here via the PlatformEventData struct.
 *
 * Results:
 *	None.
 *
 * Side effects:
 *	- If adding a new file descriptor, a PlatformEventData struct will be
 *	  allocated and associated with filePtr.
 *	- fstat is called on the file descriptor; if it is associated with
 *	  a regular file (S_IFREG,) filePtr is considered to be ready for I/O
 *	  and added to or deleted from the corresponding list in tsdPtr.
 *	- If it is not associated with a regular file, the file descriptor is
 *	  added, modified concerning its mask of events of interest, or
 *	  deleted from the epoll file descriptor of the calling thread.
 *	- If deleting a file descriptor, kevent(2) is called twice specifying
 *	  EVFILT_READ first and then EVFILT_WRITE (see note below.)
 *
 *----------------------------------------------------------------------
 */

void
PlatformEventsControl(
    FileHandler *filePtr,
    ThreadSpecificData *tsdPtr,
    int op,
    int isNew)
{
    int numChanges;
    struct kevent changeList[2];
    struct PlatformEventData *newPedPtr;
    struct stat fdStat;

    if (isNew) {
        newPedPtr = (struct PlatformEventData *)ckalloc(sizeof(struct PlatformEventData));
        newPedPtr->filePtr = filePtr;
        newPedPtr->tsdPtr = tsdPtr;
        filePtr->pedPtr = newPedPtr;
    }

    /*
     * N.B. As discussed in Tcl_WaitForEvent(), kqueue(2) does not reproduce
     * the `always ready' {select,poll}(2) behaviour for regular files
     * (S_IFREG) prior to FreeBSD 11.0-RELEASE. Therefore, filePtr is in these
     * cases simply added or deleted from the list of FileHandlers associated
     * with regular files belonging to tsdPtr.
     */

    if (fstat(filePtr->fd, &fdStat) == -1) {
	Tcl_Panic("fstat: %s", strerror(errno));
    } else if ((fdStat.st_mode & S_IFMT) == S_IFREG) {
	switch (op) {
	case EV_ADD:
	    if (isNew) {
		LIST_INSERT_HEAD(&tsdPtr->firstReadyFileHandlerPtr, filePtr,
			readyNode);
	    }
	    break;
	case EV_DELETE:
	    LIST_REMOVE(filePtr, readyNode);
	    break;
	}
	return;
    }

    numChanges = 0;
    switch (op) {
    case EV_ADD:
	if (filePtr->mask & (TCL_READABLE | TCL_EXCEPTION)) {
	    EV_SET(&changeList[numChanges], (uintptr_t)filePtr->fd,
		    EVFILT_READ, op, 0, 0, filePtr->pedPtr);
	    numChanges++;
	}
	if (filePtr->mask & TCL_WRITABLE) {
	    EV_SET(&changeList[numChanges], (uintptr_t)filePtr->fd,
		    EVFILT_WRITE, op, 0, 0, filePtr->pedPtr);
	    numChanges++;
	}
        if (numChanges) {
	    if (kevent(tsdPtr->eventsFd, changeList, numChanges, NULL, 0,
		    NULL) == -1) {
		Tcl_Panic("kevent: %s", strerror(errno));
	    }
	}
	break;
    case EV_DELETE:
	/*
	 * N.B. kqueue(2) has separate filters for readability and writability
	 * fd events. We therefore need to ensure that fds are ompletely
	 * removed from the kqueue(2) fd when deleting.  This is exacerbated
	 * by changes to filePtr->mask w/o calls to PlatforEventsControl()
	 * after e.g. an exec(3) in a child process.
	 *
	 * As one of these calls can fail, two separate kevent(2) calls are
	 * made for EVFILT_{READ,WRITE}.
	 */
	EV_SET(&changeList[0], (uintptr_t)filePtr->fd, EVFILT_READ, op, 0, 0,
		NULL);
	if ((kevent(tsdPtr->eventsFd, changeList, 1, NULL, 0, NULL) == -1)
		&& (errno != ENOENT)) {
	    Tcl_Panic("kevent: %s", strerror(errno));
	}
	EV_SET(&changeList[0], (uintptr_t)filePtr->fd, EVFILT_WRITE, op, 0, 0,
		NULL);
	if ((kevent(tsdPtr->eventsFd, changeList, 1, NULL, 0, NULL) == -1)
		&& (errno != ENOENT)) {
	    Tcl_Panic("kevent: %s", strerror(errno));
	}
	break;
    }
}

/*
 *----------------------------------------------------------------------
 *
 * PlatformEventsFinalize --
 *
 *	This function closes the pipe and the kqueue file descriptors and
 *	frees the kevent structs owned by the thread of the caller.  The above
 *	operations are protected by tsdPtr->notifierMutex, which is destroyed
 *	thereafter.
 *
 * Results:
 *	None.
 *
 * Side effects:
 * 	While tsdPtr->notifierMutex is held:
 *	The per-thread pipe(2) fds are closed, if non-zero, and set to -1.
 *	The per-thread kqueue(2) fd is closed, if non-zero, and set to 0.
 *	The per-thread kevent structs are freed, if any, and set to 0.
 *
 *	tsdPtr->notifierMutex is destroyed.
 *
 *----------------------------------------------------------------------
 */

void
PlatformEventsFinalize(
    void)
{
    ThreadSpecificData *tsdPtr = TCL_TSD_INIT(&dataKey);

    pthread_mutex_lock(&tsdPtr->notifierMutex);
    if (tsdPtr->triggerPipe[0]) {
	close(tsdPtr->triggerPipe[0]);
	tsdPtr->triggerPipe[0] = -1;
    }
    if (tsdPtr->triggerPipe[1]) {
	close(tsdPtr->triggerPipe[1]);
	tsdPtr->triggerPipe[1] = -1;
    }
    if (tsdPtr->eventsFd > 0) {
	close(tsdPtr->eventsFd);
	tsdPtr->eventsFd = 0;
    }
    if (tsdPtr->readyEvents) {
	ckfree(tsdPtr->readyEvents);
	tsdPtr->maxReadyEvents = 0;
    }
    pthread_mutex_unlock(&tsdPtr->notifierMutex);
    if ((errno = pthread_mutex_destroy(&tsdPtr->notifierMutex))) {
	Tcl_Panic("pthread_mutex_destroy: %s", strerror(errno));
    }
}

/*
 *----------------------------------------------------------------------
 *
 * PlatformEventsInit --
 *
 *	This function abstracts creating a kqueue fd via the kqueue system
 *	call and allocating memory for the kevents structs in tsdPtr for the
 *	thread of the caller.
 *
 * Results:
 *	None.
 *
 * Side effects:
 *	The following per-thread entities are initialised:
 *	- notifierMutex is initialised.
 *	- The pipe(2) is created; fcntl(2) is called on both fds to set
 *	  FD_CLOEXEC and O_NONBLOCK.
 *	- The kqueue(2) fd is created; fcntl(2) is called on it to set
 *	  FD_CLOEXEC.
 *	- A FileHandler struct is allocated and initialised for the event-
 *	  fd(2), registering interest for TCL_READABLE on it via Platform-
 *	  EventsControl().
 *	- readyEvents and maxReadyEvents are initialised with 512 kevents.
 *
 *----------------------------------------------------------------------
 */

void
PlatformEventsInit(void)
{
    ThreadSpecificData *tsdPtr = TCL_TSD_INIT(&dataKey);
    int i, fdFl;
    FileHandler *filePtr;

    errno = pthread_mutex_init(&tsdPtr->notifierMutex, NULL);
    if (errno) {
	Tcl_Panic("Tcl_InitNotifier: %s", "could not create mutex");
    }
    if (pipe(tsdPtr->triggerPipe) != 0) {
	Tcl_Panic("Tcl_InitNotifier: %s", "could not create trigger pipe");
    } else for (i = 0; i < 2; i++) {
	if (fcntl(tsdPtr->triggerPipe[i], F_SETFD, FD_CLOEXEC) == -1) {
	    Tcl_Panic("fcntl: %s", strerror(errno));
	} else {
	    fdFl = fcntl(tsdPtr->triggerPipe[i], F_GETFL);
	    fdFl |= O_NONBLOCK;
	}
	if (fcntl(tsdPtr->triggerPipe[i], F_SETFL, fdFl) == -1) {
	    Tcl_Panic("fcntl: %s", strerror(errno));
	}
    }
    if ((tsdPtr->eventsFd = kqueue()) == -1) {
	Tcl_Panic("kqueue: %s", strerror(errno));
    } else if (fcntl(tsdPtr->eventsFd, F_SETFD, FD_CLOEXEC) == -1) {
	Tcl_Panic("fcntl: %s", strerror(errno));
    }
    filePtr = (FileHandler *)ckalloc(sizeof(FileHandler));
    filePtr->fd = tsdPtr->triggerPipe[0];
    filePtr->mask = TCL_READABLE;
    PlatformEventsControl(filePtr, tsdPtr, EV_ADD, 1);
    if (!tsdPtr->readyEvents) {
        tsdPtr->maxReadyEvents = 512;
	tsdPtr->readyEvents = (struct kevent *)ckalloc(
		tsdPtr->maxReadyEvents * sizeof(tsdPtr->readyEvents[0]));
    }
    LIST_INIT(&tsdPtr->firstReadyFileHandlerPtr);
}

/*
 *----------------------------------------------------------------------
 *
 * PlatformEventsTranslate --
 *
 *	This function translates the platform-specific mask of returned
 *	events in eventPtr to a mask of TCL_* bits.
 *
 * Results:
 *	Returns the translated mask.
 *
 * Side effects:
 *	None.
 *
 *----------------------------------------------------------------------
 */

int
PlatformEventsTranslate(
    struct kevent *eventPtr)
{
    int mask;

    mask = 0;
    if (eventPtr->filter == EVFILT_READ) {
	mask |= TCL_READABLE;
	if (eventPtr->flags & EV_ERROR) {
	    mask |= TCL_EXCEPTION;
	}
    }
    if (eventPtr->filter == EVFILT_WRITE) {
	mask |= TCL_WRITABLE;
	if (eventPtr->flags & EV_ERROR) {
	    mask |= TCL_EXCEPTION;
	}
    }
    return mask;
}

/*
 *----------------------------------------------------------------------
 *
 * PlatformEventsWait --
 *
 *	This function abstracts waiting for I/O events via the kevent system
 *	call.
 *
 * Results:
 *	Returns -1 if kevent failed. Returns 0 if polling and if no events
 *	became available whilst polling. Returns a pointer to and the count of
 *	all returned events in all other cases.
 *
 * Side effects:
 *	gettimeofday(2), kevent(2), and gettimeofday(2) are called, in the
 *	specified order.
 *	If timePtr specifies a positive value, it is updated to reflect the
 *	amount of time that has passed; if its value would {under, over}flow,
 *	it is set to zero.
 *
 *----------------------------------------------------------------------
 */

int
PlatformEventsWait(
    struct kevent *events,
    size_t numEvents,
    struct timeval *timePtr)
{
    int numFound;
    struct timeval tv0, tv1, tv_delta;
    struct timespec timeout, *timeoutPtr;

    ThreadSpecificData *tsdPtr = TCL_TSD_INIT(&dataKey);

    /*
     * If timePtr is NULL, kevent(2) will wait indefinitely. If it specifies a
     * timeout of {0,0}, kevent(2) will poll. Otherwise, the timeout will
     * simply be converted to a timespec.
     */

    if (!timePtr) {
	timeoutPtr = NULL;
    } else if (!timePtr->tv_sec && !timePtr->tv_usec) {
	timeout.tv_sec = 0;
	timeout.tv_nsec = 0;
	timeoutPtr = &timeout;
    } else {
	timeout.tv_sec = timePtr->tv_sec;
	timeout.tv_nsec = timePtr->tv_usec * 1000;
	timeoutPtr = &timeout;
    }

    /*
     * Call (and possibly block on) kevent(2) and substract the delta of
     * gettimeofday(2) before and after the call from timePtr if the latter is
     * not NULL. Return the number of events returned by kevent(2).
     */

    gettimeofday(&tv0, NULL);
    numFound = kevent(tsdPtr->eventsFd, NULL, 0, events, (int) numEvents,
	    timeoutPtr);
    gettimeofday(&tv1, NULL);
    if (timePtr && (timePtr->tv_sec && timePtr->tv_usec)) {
	timersub(&tv1, &tv0, &tv_delta);
	if (!timercmp(&tv_delta, timePtr, >)) {
	    timersub(timePtr, &tv_delta, timePtr);
	} else {
	    timePtr->tv_sec = 0;
	    timePtr->tv_usec = 0;
	}
    }
    return numFound;
}

/*
 *----------------------------------------------------------------------
 *
 * Tcl_CreateFileHandler --
 *
 *	This function registers a file handler with the kqueue notifier
 *	of the thread of the caller.
 *
 * Results:
 *	None.
 *
 * Side effects:
 *	Creates a new file handler structure.
 *	PlatformEventsControl() is called for the new file handler structure.
 *
 *----------------------------------------------------------------------
 */

void
Tcl_CreateFileHandler(
    int fd,			/* Handle of stream to watch. */
    int mask,			/* OR'ed combination of TCL_READABLE,
				 * TCL_WRITABLE, and TCL_EXCEPTION: indicates
				 * conditions under which proc should be
				 * called. */
    Tcl_FileProc *proc,		/* Function to call for each selected
				 * event. */
    ClientData clientData)	/* Arbitrary data to pass to proc. */
{
    int isNew;

    if (tclNotifierHooks.createFileHandlerProc) {
	tclNotifierHooks.createFileHandlerProc(fd, mask, proc, clientData);
	return;
    } else {
	ThreadSpecificData *tsdPtr = TCL_TSD_INIT(&dataKey);
	FileHandler *filePtr;

	for (filePtr = tsdPtr->firstFileHandlerPtr; filePtr != NULL;
		filePtr = filePtr->nextPtr) {
	    if (filePtr->fd == fd) {
		break;
	    }
	}
	if (filePtr == NULL) {
	    filePtr = (FileHandler *)ckalloc(sizeof(FileHandler));
	    filePtr->fd = fd;
	    filePtr->readyMask = 0;
	    filePtr->nextPtr = tsdPtr->firstFileHandlerPtr;
	    tsdPtr->firstFileHandlerPtr = filePtr;
	    isNew = 1;
	} else {
	    isNew = 0;
	}
	filePtr->proc = proc;
	filePtr->clientData = clientData;
	filePtr->mask = mask;

	PlatformEventsControl(filePtr, tsdPtr, EV_ADD, isNew);
    }
}

/*
 *----------------------------------------------------------------------
 *
 * Tcl_DeleteFileHandler --
 *
 *	Cancel a previously-arranged callback arrangement for a file on the
 *	kqueue of the thread of the caller.
 *
 * Results:
 *	None.
 *
 * Side effects:
 *	If a callback was previously registered on file, remove it.
 *	PlatformEventsControl() is called for the file handler structure.
 *	The PlatformEventData struct associated with the new file handler
 *	structure is freed.
 *
 *----------------------------------------------------------------------
 */

void
Tcl_DeleteFileHandler(
    int fd)			/* Stream id for which to remove callback
				 * function. */
{
    if (tclNotifierHooks.deleteFileHandlerProc) {
	tclNotifierHooks.deleteFileHandlerProc(fd);
	return;
    } else {
	FileHandler *filePtr, *prevPtr;
	ThreadSpecificData *tsdPtr = TCL_TSD_INIT(&dataKey);

	/*
	 * Find the entry for the given file (and return if there isn't one).
	 */

	for (prevPtr = NULL, filePtr = tsdPtr->firstFileHandlerPtr; ;
		prevPtr = filePtr, filePtr = filePtr->nextPtr) {
	    if (filePtr == NULL) {
		return;
	    }
	    if (filePtr->fd == fd) {
		break;
	    }
	}

	/*
	 * Update the check masks for this file.
	 */

	PlatformEventsControl(filePtr, tsdPtr, EV_DELETE, 0);
	if (filePtr->pedPtr) {
	    ckfree(filePtr->pedPtr);
	}

	/*
	 * Clean up information in the callback record.
	 */

	if (prevPtr == NULL) {
	    tsdPtr->firstFileHandlerPtr = filePtr->nextPtr;
	} else {
	    prevPtr->nextPtr = filePtr->nextPtr;
	}
	ckfree(filePtr);
    }
}

/*
 *----------------------------------------------------------------------
 *
 * Tcl_WaitForEvent --
 *
 *	This function is called by Tcl_DoOneEvent to wait for new events on
 *	the message queue. If the block time is 0, then Tcl_WaitForEvent just
 *	polls without blocking.
 *
 *	The waiting logic is implemented in PlatformEventsWait.
 *
 * Results:
 *	Returns -1 if PlatformEventsWait() would block forever, otherwise
 *	returns 0.
 *
 * Side effects:
 *	Queues file events that are detected by PlatformEventsWait().
 *
 *----------------------------------------------------------------------
 */

int
Tcl_WaitForEvent(
    const Tcl_Time *timePtr)		/* Maximum block time, or NULL. */
{
    if (tclNotifierHooks.waitForEventProc) {
	return tclNotifierHooks.waitForEventProc(timePtr);
    } else {
	FileHandler *filePtr;
	int mask;
	Tcl_Time vTime;
	/*
	 * Impl. notes: timeout & timeoutPtr are used if, and only if threads
	 * are not enabled. They are the arguments for the regular epoll_wait()
	 * used when the core is not thread-enabled.
	 */

	struct timeval timeout, *timeoutPtr;
	int numFound, numEvent;
	struct PlatformEventData *pedPtr;
	ThreadSpecificData *tsdPtr = TCL_TSD_INIT(&dataKey);
	int numQueued;
	ssize_t i;
	char buf[1];

	/*
	 * Set up the timeout structure. Note that if there are no events to
	 * check for, we return with a negative result rather than blocking
	 * forever.
	 */

	if (timePtr != NULL) {
	    /*
	     * TIP #233 (Virtualized Time). Is virtual time in effect? And do
	     * we actually have something to scale? If yes to both then we
	     * call the handler to do this scaling.
	     */

	    if (timePtr->sec != 0 || timePtr->usec != 0) {
		vTime = *timePtr;
		tclScaleTimeProcPtr(&vTime, tclTimeClientData);
		timePtr = &vTime;
	    }
	    timeout.tv_sec = timePtr->sec;
	    timeout.tv_usec = timePtr->usec;
	    timeoutPtr = &timeout;
	} else {
	    timeoutPtr = NULL;
	}

	/*
	 * Walk the list of FileHandlers associated with regular files
	 * (S_IFREG) belonging to tsdPtr, queue Tcl events for them, and
	 * update their mask of events of interest.
	 *
	 * kqueue(2), unlike epoll(7), does support regular files, but
	 * EVFILT_READ only `[r]eturns when the file pointer is not at the end
	 * of file' as opposed to unconditionally. While FreeBSD 11.0-RELEASE
	 * adds support for this mode (NOTE_FILE_POLL,) this is not used for
	 * reasons of compatibility.
	 *
	 * Therefore, the behaviour of {select,poll}(2) is simply simulated
	 * here: fds associated with regular files are added to this list by
	 * PlatformEventsControl() and processed here before calling (and
	 * possibly blocking) on PlatformEventsWait().
	 */

	numQueued = 0;
	LIST_FOREACH(filePtr, &tsdPtr->firstReadyFileHandlerPtr, readyNode) {
	    mask = 0;
	    if (filePtr->mask & TCL_READABLE) {
		mask |= TCL_READABLE;
	    }
	    if (filePtr->mask & TCL_WRITABLE) {
		mask |= TCL_WRITABLE;
	    }

	    /*
	     * Don't bother to queue an event if the mask was previously
	     * non-zero since an event must still be on the queue.
	     */

	    if (filePtr->readyMask == 0) {
		FileHandlerEvent *fileEvPtr = (FileHandlerEvent *)
			ckalloc(sizeof(FileHandlerEvent));

		fileEvPtr->header.proc = FileHandlerEventProc;
		fileEvPtr->fd = filePtr->fd;
		Tcl_QueueEvent((Tcl_Event *) fileEvPtr, TCL_QUEUE_TAIL);
		numQueued++;
	    }
	    filePtr->readyMask = mask;
	}

	/*
	 * If any events were queued in the above loop, force PlatformEvents-
	 * Wait() to poll as there already are events that need to be processed
	 * at this point.
	 */

	if (numQueued) {
	    timeout.tv_sec = 0;
	    timeout.tv_usec = 0;
	    timeoutPtr = &timeout;
	}

	/*
	 * Wait or poll for new events, queue Tcl events for the FileHandlers
	 * corresponding to them, and update the FileHandlers' mask of events
	 * of interest registered by the last call to Tcl_CreateFileHandler().
	 *
	 * Events for the trigger pipe are processed here in order to facilitate
	 * inter-thread IPC. If another thread intends to wake up this thread
	 * whilst it's blocking on PlatformEventsWait(), it write(2)s to the
	 * other end of the pipe (see Tcl_AlertNotifier(),) which in turn will
	 * cause PlatformEventsWait() to return immediately.
	 */

	numFound = PlatformEventsWait(tsdPtr->readyEvents,
		tsdPtr->maxReadyEvents, timeoutPtr);
	for (numEvent = 0; numEvent < numFound; numEvent++) {
	    pedPtr = (struct PlatformEventData *)
		    tsdPtr->readyEvents[numEvent].udata;
	    filePtr = pedPtr->filePtr;
	    mask = PlatformEventsTranslate(&tsdPtr->readyEvents[numEvent]);
	    if (filePtr->fd == tsdPtr->triggerPipe[0]) {
		i = read(tsdPtr->triggerPipe[0], buf, 1);
		if ((i == -1) && (errno != EAGAIN)) {
		    Tcl_Panic("Tcl_WaitForEvent: read from %p->triggerPipe: %s",
			    (void *) tsdPtr, strerror(errno));
		}
		continue;
	    }
	    if (!mask) {
		continue;
	    }

	    /*
	     * Don't bother to queue an event if the mask was previously
	     * non-zero since an event must still be on the queue.
	     */

	    if (filePtr->readyMask == 0) {
		FileHandlerEvent *fileEvPtr = (FileHandlerEvent *)
			ckalloc(sizeof(FileHandlerEvent));

		fileEvPtr->header.proc = FileHandlerEventProc;
		fileEvPtr->fd = filePtr->fd;
		Tcl_QueueEvent((Tcl_Event *) fileEvPtr, TCL_QUEUE_TAIL);
	    }
	    filePtr->readyMask |= mask;
	}
	return 0;
    }
}

#endif /* NOTIFIER_KQUEUE && TCL_THREADS */
#endif /* !HAVE_COREFOUNDATION */

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