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diff --git a/doc/Thread.3 b/doc/Thread.3 new file mode 100644 index 0000000..595fac3 --- /dev/null +++ b/doc/Thread.3 @@ -0,0 +1,100 @@ +'\" +'\" Copyright (c) 1998 Sun Microsystems, Inc. +'\" +'\" See the file "license.terms" for information on usage and redistribution +'\" of this file, and for a DISCLAIMER OF ALL WARRANTIES. +'\" +'\" RCS: @(#) $Id: Thread.3,v 1.2 1999/04/16 00:46:33 stanton Exp $ +'\" +.so man.macros +.TH Tcl_ConditionNotify 3 "8.1" Tcl "Tcl Library Procedures" +.BS +.SH NAME +Tcl_ConditionNotify, Tcl_ConditionWait, Tcl_GetThreadData, Tcl_MutexLock, Tcl_MutexUnlock \- thread synchronization support. +.SH SYNOPSIS +.nf +\fB#include <tcl.h>\fR +.sp +void +\fBTcl_ConditionNotify\fR(\fIcondPtr\fR) +.sp +void +\fBTcl_ConditionWait\fR(\fIcondPtr, mutexPtr, timePtr\fR) +.sp +VOID * +\fBTcl_GetThreadData\fR(\fIkeyPtr, size\fR) +.sp +void +\fBTcl_MutexLock\fR(\fImutexPtr\fR) +.sp +void +\fBTcl_MutexUnlock\fR(\fImutexPtr\fR) +.SH ARGUMENTS +.AS Tcl_ThreadDataKey *keyPtr +.AP Tcl_Condition *condPtr in +A condition variable, which must be associated with a mutex lock. +.AP Tcl_Condition *mutexPtr in +A mutex lock. +.AP Tcl_Time *timePtr in +A time limit on the condition wait. NULL to wait forever. +Note that a polling value of 0 seconds doesn't make much sense. +.AP Tcl_ThreadDataKey *keyPtr in +This identifies a block of thread local storage. The key should be +static and process-wide, yet each thread will end up associating +a different block of storage with this key. +.AP int *size in +The size of the thread local storage block. This amount of data +is allocated and initialized to zero the first time each thread +calls \fBTcl_GetThreadData\fR. +.BE + +.SH DESCRIPTION +.PP +A mutex is a lock that is used to serialize all threads through a piece +of code by calling \fBTcl_MutexLock\fR and \fBTcl_MutexUnlock\fR. +If one thread holds a mutex, any other thread calling \fBTcl_MutexLock\fR will +block until \fBTcl_MutexUnlock\fR is called. +.VS +The result of locking a mutex twice from the same thread is undefined. +On some platforms it will result in a deadlock. +.VE +\fBTcl_MutexLock\fR and \fBTcl_MutexUnlock\fR +procedures are defined as empty macros if not compiling with threads enabled. +.PP +A condition variable is used as a signaling mechanism: +a thread can lock a mutex and then wait on a condition variable +with \fBTcl_ConditionWait\fR. This atomically releases the mutex lock +and blocks the waiting thread until another thread calls +\fBTcl_ConditionNotify\fR. The caller of \fBTcl_ConditionNotify\fR should +have the associated mutex held by previously calling \fBTcl_MutexLock\fR, +but this is not enforced. Notifying the +condition variable unblocks all threads waiting on the condition variable, +but they do not proceed until the mutex is released with \fBTcl_MutexUnlock\fR. +The implementation of \fBTcl_ConditionWait\fR automatically locks +the mutex before returning. +.PP +The caller of \fBTcl_ConditionWait\fR should be prepared for spurious +notifications by calling \fBTcl_ConditionWait\fR within a while loop +that tests some invariant. +.PP +The \fBTcl_GetThreadData\fR call returns a pointer to a block of +thread-private data. Its argument is a key that is shared by all threads +and a size for the block of storage. The storage is automatically +allocated and initialized to all zeros the first time each thread asks for it. +The storage is automatically deallocated by \fBTcl_FinalizeThread\fR +.SH INITIALIZATION +.PP +.PP +All of these synchronization objects are self initializing. +They are implemented as opaque pointers that should be NULL +upon first use. +The mutexes and condition variables are +cleaned up by process exit handlers. Thread local storage is +reclaimed during \fBTcl_FinalizeThread\fR. +.SH CREATING THREADS +The API to create threads is not finalized at this time. +There are private facilities to create threads that contain a new +Tcl interpreter, and to send scripts among threads. +Dive into tclThreadTest.c and tclThread.c for examples. +.SH KEYWORDS +thread, mutex, condition variable, thread local storage |