'\" '\" Copyright (c) 1999 Scriptics Corporation '\" 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. '\" .TH Threads 3tcl "8.1" Tcl "Tcl Library Procedures" .\" The -*- nroff -*- definitions below are for supplemental macros used .\" in Tcl/Tk manual entries. .\" .\" .AP type name in/out ?indent? .\" Start paragraph describing an argument to a library procedure. .\" type is type of argument (int, etc.), in/out is either "in", "out", .\" or "in/out" to describe whether procedure reads or modifies arg, .\" and indent is equivalent to second arg of .IP (shouldn't ever be .\" needed; use .AS below instead) .\" .\" .AS ?type? ?name? .\" Give maximum sizes of arguments for setting tab stops. Type and .\" name are examples of largest possible arguments that will be passed .\" to .AP later. If args are omitted, default tab stops are used. .\" .\" .BS .\" Start box enclosure. From here until next .BE, everything will be .\" enclosed in one large box. .\" .\" .BE .\" End of box enclosure. .\" .\" .CS .\" Begin code excerpt. .\" .\" .CE .\" End code excerpt. .\" .\" .VS ?version? ?br? .\" Begin vertical sidebar, for use in marking newly-changed parts .\" of man pages. The first argument is ignored and used for recording .\" the version when the .VS was added, so that the sidebars can be .\" found and removed when they reach a certain age. If another argument .\" is present, then a line break is forced before starting the sidebar. .\" .\" .VE .\" End of vertical sidebar. .\" .\" .DS .\" Begin an indented unfilled display. .\" .\" .DE .\" End of indented unfilled display. .\" .\" .SO ?manpage? .\" Start of list of standard options for a Tk widget. The manpage .\" argument defines where to look up the standard options; if .\" omitted, defaults to "options". The options follow on successive .\" lines, in three columns separated by tabs. .\" .\" .SE .\" End of list of standard options for a Tk widget. .\" .\" .OP cmdName dbName dbClass .\" Start of description of a specific option. cmdName gives the .\" option's name as specified in the class command, dbName gives .\" the option's name in the option database, and dbClass gives .\" the option's class in the option database. .\" .\" .UL arg1 arg2 .\" Print arg1 underlined, then print arg2 normally. .\" .\" .QW arg1 ?arg2? .\" Print arg1 in quotes, then arg2 normally (for trailing punctuation). .\" .\" .PQ arg1 ?arg2? .\" Print an open parenthesis, arg1 in quotes, then arg2 normally .\" (for trailing punctuation) and then a closing parenthesis. .\" .\" # Set up traps and other miscellaneous stuff for Tcl/Tk man pages. .if t .wh -1.3i ^B .nr ^l \n(.l .ad b .\" # Start an argument description .de AP .ie !"\\$4"" .TP \\$4 .el \{\ . ie !"\\$2"" .TP \\n()Cu . el .TP 15 .\} .ta \\n()Au \\n()Bu .ie !"\\$3"" \{\ \&\\$1 \\fI\\$2\\fP (\\$3) .\".b .\} .el \{\ .br .ie !"\\$2"" \{\ \&\\$1 \\fI\\$2\\fP .\} .el \{\ \&\\fI\\$1\\fP .\} .\} .. .\" # define tabbing values for .AP .de AS .nr )A 10n .if !"\\$1"" .nr )A \\w'\\$1'u+3n .nr )B \\n()Au+15n .\" .if !"\\$2"" .nr )B \\w'\\$2'u+\\n()Au+3n .nr )C \\n()Bu+\\w'(in/out)'u+2n .. .AS Tcl_Interp Tcl_CreateInterp in/out .\" # BS - start boxed text .\" # ^y = starting y location .\" # ^b = 1 .de BS .br .mk ^y .nr ^b 1u .if n .nf .if n .ti 0 .if n \l'\\n(.lu\(ul' .if n .fi .. .\" # BE - end boxed text (draw box now) .de BE .nf .ti 0 .mk ^t .ie n \l'\\n(^lu\(ul' .el \{\ .\" Draw four-sided box normally, but don't draw top of .\" box if the box started on an earlier page. .ie !\\n(^b-1 \{\ \h'-1.5n'\L'|\\n(^yu-1v'\l'\\n(^lu+3n\(ul'\L'\\n(^tu+1v-\\n(^yu'\l'|0u-1.5n\(ul' .\} .el \}\ \h'-1.5n'\L'|\\n(^yu-1v'\h'\\n(^lu+3n'\L'\\n(^tu+1v-\\n(^yu'\l'|0u-1.5n\(ul' .\} .\} .fi .br .nr ^b 0 .. .\" # VS - start vertical sidebar .\" # ^Y = starting y location .\" # ^v = 1 (for troff; for nroff this doesn't matter) .de VS .if !"\\$2"" .br .mk ^Y .ie n 'mc \s12\(br\s0 .el .nr ^v 1u .. .\" # VE - end of vertical sidebar .de VE .ie n 'mc .el \{\ .ev 2 .nf .ti 0 .mk ^t \h'|\\n(^lu+3n'\L'|\\n(^Yu-1v\(bv'\v'\\n(^tu+1v-\\n(^Yu'\h'-|\\n(^lu+3n' .sp -1 .fi .ev .\} .nr ^v 0 .. .\" # Special macro to handle page bottom: finish off current .\" # box/sidebar if in box/sidebar mode, then invoked standard .\" # page bottom macro. .de ^B .ev 2 'ti 0 'nf .mk ^t .if \\n(^b \{\ .\" Draw three-sided box if this is the box's first page, .\" draw two sides but no top otherwise. .ie !\\n(^b-1 \h'-1.5n'\L'|\\n(^yu-1v'\l'\\n(^lu+3n\(ul'\L'\\n(^tu+1v-\\n(^yu'\h'|0u'\c .el \h'-1.5n'\L'|\\n(^yu-1v'\h'\\n(^lu+3n'\L'\\n(^tu+1v-\\n(^yu'\h'|0u'\c .\} .if \\n(^v \{\ .nr ^x \\n(^tu+1v-\\n(^Yu \kx\h'-\\nxu'\h'|\\n(^lu+3n'\ky\L'-\\n(^xu'\v'\\n(^xu'\h'|0u'\c .\} .bp 'fi .ev .if \\n(^b \{\ .mk ^y .nr ^b 2 .\} .if \\n(^v \{\ .mk ^Y .\} .. .\" # DS - begin display .de DS .RS .nf .sp .. .\" # DE - end display .de DE .fi .RE .sp .. .\" # SO - start of list of standard options .de SO 'ie '\\$1'' .ds So \\fBoptions\\fR 'el .ds So \\fB\\$1\\fR .SH "STANDARD OPTIONS" .LP .nf .ta 5.5c 11c .ft B .. .\" # SE - end of list of standard options .de SE .fi .ft R .LP See the \\*(So manual entry for details on the standard options. .. .\" # OP - start of full description for a single option .de OP .LP .nf .ta 4c Command-Line Name: \\fB\\$1\\fR Database Name: \\fB\\$2\\fR Database Class: \\fB\\$3\\fR .fi .IP .. .\" # CS - begin code excerpt .de CS .RS .nf .ta .25i .5i .75i 1i .. .\" # CE - end code excerpt .de CE .fi .RE .. .\" # UL - underline word .de UL \\$1\l'|0\(ul'\\$2 .. .\" # QW - apply quotation marks to word .de QW .ie '\\*(lq'"' ``\\$1''\\$2 .\"" fix emacs highlighting .el \\*(lq\\$1\\*(rq\\$2 .. .\" # PQ - apply parens and quotation marks to word .de PQ .ie '\\*(lq'"' (``\\$1''\\$2)\\$3 .\"" fix emacs highlighting .el (\\*(lq\\$1\\*(rq\\$2)\\$3 .. .\" # QR - quoted range .de QR .ie '\\*(lq'"' ``\\$1''\\-``\\$2''\\$3 .\"" fix emacs highlighting .el \\*(lq\\$1\\*(rq\\-\\*(lq\\$2\\*(rq\\$3 .. .\" # MT - "empty" string .de MT .QW "" .. .BS .SH NAME Tcl_ConditionNotify, Tcl_ConditionWait, Tcl_ConditionFinalize, Tcl_GetThreadData, Tcl_MutexLock, Tcl_MutexUnlock, Tcl_MutexFinalize, Tcl_CreateThread, Tcl_JoinThread \- Tcl thread support .SH SYNOPSIS .nf \fB#include \fR .sp void \fBTcl_ConditionNotify\fR(\fIcondPtr\fR) .sp void \fBTcl_ConditionWait\fR(\fIcondPtr, mutexPtr, timePtr\fR) .sp void \fBTcl_ConditionFinalize\fR(\fIcondPtr\fR) .sp Void * \fBTcl_GetThreadData\fR(\fIkeyPtr, size\fR) .sp void \fBTcl_MutexLock\fR(\fImutexPtr\fR) .sp void \fBTcl_MutexUnlock\fR(\fImutexPtr\fR) .sp void \fBTcl_MutexFinalize\fR(\fImutexPtr\fR) .sp int \fBTcl_CreateThread\fR(\fIidPtr, proc, clientData, stackSize, flags\fR) .sp int \fBTcl_JoinThread\fR(\fIid, result\fR) .SH ARGUMENTS .AS Tcl_CreateThreadProc proc out .AP Tcl_Condition *condPtr in A condition variable, which must be associated with a mutex lock. .AP Tcl_Mutex *mutexPtr in A mutex lock. .AP "const Tcl_Time" *timePtr in A time limit on the condition wait. NULL to wait forever. Note that a polling value of 0 seconds does not 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. .AP Tcl_ThreadId *idPtr out The referred storage will contain the id of the newly created thread as returned by the operating system. .AP Tcl_ThreadId id in Id of the thread waited upon. .AP Tcl_ThreadCreateProc *proc in This procedure will act as the \fBmain()\fR of the newly created thread. The specified \fIclientData\fR will be its sole argument. .AP ClientData clientData in Arbitrary information. Passed as sole argument to the \fIproc\fR. .AP int stackSize in The size of the stack given to the new thread. .AP int flags in Bitmask containing flags allowing the caller to modify behavior of the new thread. .AP int *result out The referred storage is used to place the exit code of the thread waited upon into it. .BE .SH INTRODUCTION Beginning with the 8.1 release, the Tcl core is thread safe, which allows you to incorporate Tcl into multithreaded applications without customizing the Tcl core. Starting with the 8.6 release, Tcl multithreading support is on by default. To disable Tcl multithreading support, you must include the \fB\-\|\-disable-threads\fR option to \fBconfigure\fR when you configure and compile your Tcl core. .PP An important constraint of the Tcl threads implementation is that \fIonly the thread that created a Tcl interpreter can use that interpreter\fR. In other words, multiple threads can not access the same Tcl interpreter. (However, a single thread can safely create and use multiple interpreters.) .SH DESCRIPTION Tcl provides \fBTcl_CreateThread\fR for creating threads. The caller can determine the size of the stack given to the new thread and modify the behavior through the supplied \fIflags\fR. The value \fBTCL_THREAD_STACK_DEFAULT\fR for the \fIstackSize\fR indicates that the default size as specified by the operating system is to be used for the new thread. As for the flags, currently only the values \fBTCL_THREAD_NOFLAGS\fR and \fBTCL_THREAD_JOINABLE\fR are defined. The first of them invokes the default behavior with no special settings. Using the second value marks the new thread as \fIjoinable\fR. This means that another thread can wait for the such marked thread to exit and join it. .PP Restrictions: On some UNIX systems the pthread-library does not contain the functionality to specify the stack size of a thread. The specified value for the stack size is ignored on these systems. Windows currently does not support joinable threads. This flag value is therefore ignored on this platform. .PP Tcl provides the \fBTcl_ExitThread\fR and \fBTcl_FinalizeThread\fR functions for terminating threads and invoking optional per-thread exit handlers. See the \fBTcl_Exit\fR page for more information on these procedures. .PP The \fBTcl_JoinThread\fR function is provided to allow threads to wait upon the exit of another thread, which must have been marked as joinable through usage of the \fBTCL_THREAD_JOINABLE\fR-flag during its creation via \fBTcl_CreateThread\fR. .PP Trying to wait for the exit of a non-joinable thread or a thread which is already waited upon will result in an error. Waiting for a joinable thread which already exited is possible, the system will retain the necessary information until after the call to \fBTcl_JoinThread\fR. This means that not calling \fBTcl_JoinThread\fR for a joinable thread will cause a memory leak. .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. .SS "SYNCHRONIZATION AND COMMUNICATION" Tcl provides \fBTcl_ThreadQueueEvent\fR and \fBTcl_ThreadAlert\fR for handling event queuing in multithreaded applications. See the \fBNotifier\fR manual page for more information on these procedures. .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. A mutex can be destroyed after its use by calling \fBTcl_MutexFinalize\fR. The result of locking a mutex twice from the same thread is undefined. On some platforms it will result in a deadlock. The \fBTcl_MutexLock\fR, \fBTcl_MutexUnlock\fR and \fBTcl_MutexFinalize\fR procedures are defined as empty macros if not compiling with threads enabled. For declaration of mutexes the \fBTCL_DECLARE_MUTEX\fR macro should be used. This macro assures correct mutex handling even when the core is compiled without 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 A condition variable can be destroyed after its use by calling \fBTcl_ConditionFinalize\fR. .PP The \fBTcl_ConditionNotify\fR, \fBTcl_ConditionWait\fR and \fBTcl_ConditionFinalize\fR procedures are defined as empty macros if not compiling with threads enabled. .SS INITIALIZATION .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 either cleaned up by process exit handlers (if living that long) or explicitly by calls to \fBTcl_MutexFinalize\fR or \fBTcl_ConditionFinalize\fR. Thread local storage is reclaimed during \fBTcl_FinalizeThread\fR. .SH "SCRIPT-LEVEL ACCESS TO THREADS" .PP Tcl provides no built-in commands for scripts to use to create, manage, or join threads, nor any script-level access to mutex or condition variables. It provides such facilities only via C interfaces, and leaves it up to packages to expose these matters to the script level. One such package is the \fBThread\fR package. .SH EXAMPLE .PP To create a thread with portable code, its implementation function should be declared as follows: .PP .CS static \fBTcl_ThreadCreateProc\fR MyThreadImplFunc; .CE .PP It should then be defined like this example, which just counts up to a given value and then finishes. .PP .CS static \fBTcl_ThreadCreateType\fR MyThreadImplFunc( ClientData clientData) { int i, limit = (int) clientData; for (i=0 ; i