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authorandreas_kupries <akupries@shaw.ca>2010-09-24 17:53:39 (GMT)
committerandreas_kupries <akupries@shaw.ca>2010-09-24 17:53:39 (GMT)
commit87af30e0e77b0228943003952af1742423ed0b6d (patch)
tree189b336d0b4ff26b839257006aebc30915af1c05
parenta186bdb4397f2d831f6bb04e453fdf14e21c9c97 (diff)
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* tclWinsock.c: [Bug 3056775]: Fixed race condition between thread
and internal co-thread access of a socket's structure because of the thread not using the socketListLock in TcpAccept(). Added documentation on how the module works to the top.
-rw-r--r--ChangeLog7
-rw-r--r--win/tclWinSock.c48
2 files changed, 54 insertions, 1 deletions
diff --git a/ChangeLog b/ChangeLog
index 7822654..20c82ff 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,10 @@
+2010-09-24 Andreas Kupries <andreask@activestate.com>
+
+ * tclWinsock.c: [Bug 3056775]: Fixed race condition between thread
+ and internal co-thread access of a socket's structure because of
+ the thread not using the socketListLock in TcpAccept(). Added
+ documentation on how the module works to the top.
+
2010-09-23 Jan Nijtmans <nijtmans@users.sf.net>
* generic/tclDecls.h: Make Tcl_SetPanicProc and Tcl_GetStringResult
diff --git a/win/tclWinSock.c b/win/tclWinSock.c
index b4ef80b..f3127d5 100644
--- a/win/tclWinSock.c
+++ b/win/tclWinSock.c
@@ -8,7 +8,43 @@
* See the file "license.terms" for information on usage and redistribution of
* this file, and for a DISCLAIMER OF ALL WARRANTIES.
*
- * RCS: @(#) $Id: tclWinSock.c,v 1.74 2010/09/13 14:20:39 nijtmans Exp $
+ * RCS: @(#) $Id: tclWinSock.c,v 1.75 2010/09/24 17:53:39 andreas_kupries Exp $
+ *
+ * -----------------------------------------------------------------------
+ *
+ * General information on how this module works.
+ *
+ * - Each Tcl-thread with its sockets maintains an internal window to receive
+ * socket messages from the OS.
+ *
+ * - To ensure that message reception is always running this window is
+ * actually owned and handled by an internal thread. This we call the
+ * co-thread of Tcl's thread.
+ *
+ * - The whole structure is set up by InitSockets() which is called for each
+ * Tcl thread. The implementation of the co-thread is in SocketThread(),
+ * and the messages are handled by SocketProc(). The connection between
+ * both is not directly visible, it is done through a Win32 window class.
+ * This class is initialized by InitSockets() as well, and used in the
+ * creation of the message receiver windows.
+ *
+ * - An important thing to note is that *both* thread and co-thread have
+ * access to the list of sockets maintained in the private TSD data of the
+ * thread. The co-thread was given access to it upon creation through the
+ * new thread's client-data.
+ *
+ * Because of this dual access the TSD data contains an OS mutex, the
+ * "socketListLock", to mediate exclusion between thread and co-thread.
+ *
+ * The co-thread's access is all in SocketProc(). The thread's access is
+ * through SocketEventProc() (1) and the functions called by it.
+ *
+ * (Ad 1) This is the handler function for all queued socket events, which
+ * all the OS messages are translated to through the EventSource (2)
+ * driven by the OS messages.
+ *
+ * (Ad 2) The main functions for this are SocketSetupProc() and
+ * SocketCheckProc().
*/
#include "tclWinInt.h"
@@ -1463,6 +1499,12 @@ TcpAccept(
&len);
/*
+ * Protect access to sockets (acceptEventCount, readyEvents) in socketList
+ * by the lock. Fix for SF Tcl Bug 3056775.
+ */
+ WaitForSingleObject(tsdPtr->socketListLock, INFINITE);
+
+ /*
* Clear the ready mask so we can detect the next connection request. Note
* that connection requests are level triggered, so if there is a request
* already pending, a new event will be generated.
@@ -1471,6 +1513,8 @@ TcpAccept(
if (newSocket == INVALID_SOCKET) {
infoPtr->acceptEventCount = 0;
infoPtr->readyEvents &= ~(FD_ACCEPT);
+
+ SetEvent(tsdPtr->socketListLock);
return;
}
@@ -1486,6 +1530,8 @@ TcpAccept(
infoPtr->readyEvents &= ~(FD_ACCEPT);
}
+ SetEvent(tsdPtr->socketListLock);
+
/*
* Win-NT has a misfeature that sockets are inherited in child processes
* by default. Turn off the inherit bit.