1Threads(3) Tcl Library Procedures Threads(3)
2______________________________________________________________________________
6
8 Tcl_ConditionNotify, Tcl_ConditionWait, Tcl_ConditionFinalize, Tcl_Get‐
9 ThreadData, Tcl_MutexLock, Tcl_MutexUnlock, Tcl_MutexFinalize, Tcl_Cre‐
10 ateThread, Tcl_JoinThread - Tcl thread support.
11
13 #include <tcl.h>
14 void
16 Tcl_ConditionNotify(condPtr)
17 void
19 Tcl_ConditionWait(condPtr, mutexPtr, timePtr)
20 void
22 Tcl_ConditionFinalize(condPtr)
23 Void *
25 Tcl_GetThreadData(keyPtr, size)
26 void
28 Tcl_MutexLock(mutexPtr)
29 void
31 Tcl_MutexUnlock(mutexPtr)
32 void
34 Tcl_MutexFinalize(mutexPtr)
35 int
37 Tcl_CreateThread(idPtr, threadProc, clientData, stackSize, flags)
38 int
40 Tcl_JoinThread(id, result)
41
43 Tcl_Condition *condPtr (in) A condition variable, which
44 must be associated with a mutex
45 lock.
46 Tcl_Mutex *mutexPtr (in) A mutex lock.
48 Tcl_Time *timePtr (in) A time limit on the condition
50 wait. NULL to wait forever.
51 Note that a polling value of 0
52 seconds doesn't make much
53 sense.
54 Tcl_ThreadDataKey *keyPtr (in) This identifies a block of
56 thread local storage. The key
57 should be static and process-
58 wide, yet each thread will end
59 up associating a different
60 block of storage with this key.
61 int *size (in) The size of the thread local
63 storage block. This amount of
64 data is allocated and initial‐
65 ized to zero the first time
66 each thread calls Tcl_Get‐
67 ThreadData.
68 Tcl_ThreadId *idPtr (out) The referred storage will con‐
70 tain the id of the newly cre‐
71 ated thread as returned by the
72 operating system.
73 Tcl_ThreadId id (in) Id of the thread waited upon.
75 Tcl_ThreadCreateProc threadProc(in)
77 This procedure will act as the
78 main() of the newly created
79 thread. The specified client‐
80 Data will be its sole argument.
81 ClientData clientData(in) Arbitrary information. Passed
83 as sole argument to the thread‐
84 Proc.
85 int stackSize (in) The size of the stack given to
87 the new thread.
88 int flags (in) Bitmask containing flags allow‐
90 ing the caller to modify behav‐
91 iour of the new thread.
92 int *result (out) The referred storage is used to
94 place the exit code of the
95 thread waited upon into it.
96_________________________________________________________________
97
99 Beginning with the 8.1 release, the Tcl core is thread safe, which
100 allows you to incorporate Tcl into multithreaded applications without
101 customizing the Tcl core. To enable Tcl multithreading support, you
102 must include the --enable-threads option to configure when you config‐
103 ure and compile your Tcl core.
104 An important constraint of the Tcl threads implementation is that only
106 the thread that created a Tcl interpreter can use that interpreter. In
107 other words, multiple threads can not access the same Tcl interpreter.
108 (However, as was the case in previous releases, a single thread can
109 safely create and use multiple interpreters.)
110 Tcl does provide Tcl_CreateThread for creating threads. The caller can │
112 determine the size of the stack given to the new thread and modify the │
113 behaviour through the supplied flags. The value │
114 TCL_THREAD_STACK_DEFAULT for the stackSize indicates that the default │
115 size as specified by the operating system is to be used for the new │
116 thread. As for the flags, currently are only the values │
117 TCL_THREAD_NOFLAGS and TCL_THREAD_JOINABLE defined. The first of them │
118 invokes the default behaviour with no specialties. Using the second │
119 value marks the new thread as joinable. This means that another thread │
120 can wait for the such marked thread to exit and join it. │
121 Restrictions: On some unix systems the pthread-library does not contain │
123 the functionality to specify the stacksize of a thread. The specified │
124 value for the stacksize is ignored on these systems. Both Windows and │
125 Macintosh currently do not support joinable threads. This flag value is │
126 therefore ignored on these platforms.
127 Tcl does provide Tcl_ExitThread and Tcl_FinalizeThread for terminating
129 threads and invoking optional per-thread exit handlers. See the
130 Tcl_Exit page for more information on these procedures.
131 The Tcl_JoinThread function is provided to allow threads to wait upon │
133 the exit of another thread, which must have been marked as joinable │
134 through usage of the TCL_THREAD_JOINABLE-flag during its creation via │
135 Tcl_CreateThread. │
136 Trying to wait for the exit of a non-joinable thread or a thread which │
138 is already waited upon will result in an error. Waiting for a joinable │
139 thread which already exited is possible, the system will retain the │
140 necessary information until after the call to Tcl_JoinThread. This │
141 means that not calling Tcl_JoinThread for a joinable thread will cause │
142 a memory leak.
143 Tcl provides Tcl_ThreadQueueEvent and Tcl_ThreadAlert for handling
145 event queueing in multithreaded applications. See the Notifier manual
146 page for more information on these procedures.
147 In this release, the Tcl language itself provides no support for creat‐
149 ing multithreaded scripts (for example, scripts that could spawn a Tcl
150 interpreter in a separate thread). If you need to add this feature at
151 this time, see the tclThreadTest.c file in the Tcl source distribution
152 for an experimental implementation or use the Tcl "Threading Extension"
153 package implementing thread creation and management commands at the
154 script level.
155
159 A mutex is a lock that is used to serialize all threads through a piece
160 of code by calling Tcl_MutexLock and Tcl_MutexUnlock. If one thread
161 holds a mutex, any other thread calling Tcl_MutexLock will block until
162 Tcl_MutexUnlock is called. A mutex can be destroyed after its use by │
163 calling Tcl_MutexFinalize. The result of locking a mutex twice from │
164 the same thread is undefined. On some platforms it will result in a │
165 deadlock. The Tcl_MutexLock, Tcl_MutexUnlock and Tcl_MutexFinalize
166 procedures are defined as empty macros if not compiling with threads
167 enabled. For declaration of mutexes the TCL_DECLARE_MUTEX macro should
168 be used. This macro assures correct mutex handling even when the core
169 is compiled without threads enabled.
170 A condition variable is used as a signaling mechanism: a thread can
172 lock a mutex and then wait on a condition variable with Tcl_Condition‐
173 Wait. This atomically releases the mutex lock and blocks the waiting
174 thread until another thread calls Tcl_ConditionNotify. The caller of
175 Tcl_ConditionNotify should have the associated mutex held by previously
176 calling Tcl_MutexLock, but this is not enforced. Notifying the condi‐
177 tion variable unblocks all threads waiting on the condition variable,
178 but they do not proceed until the mutex is released with Tcl_MutexUn‐
179 lock. The implementation of Tcl_ConditionWait automatically locks the
180 mutex before returning.
181 The caller of Tcl_ConditionWait should be prepared for spurious notifi‐
183 cations by calling Tcl_ConditionWait within a while loop that tests
184 some invariant.
185 A condition variable can be destroyed after its use by calling Tcl_Con‐ │
187 ditionFinalize. │
188 The Tcl_ConditionNotify, Tcl_ConditionWait and Tcl_ConditionFinalize │
190 procedures are defined as empty macros if not compiling with threads │
191 enabled.
192 The Tcl_GetThreadData call returns a pointer to a block of thread-pri‐
194 vate data. Its argument is a key that is shared by all threads and a
195 size for the block of storage. The storage is automatically allocated
196 and initialized to all zeros the first time each thread asks for it.
197 The storage is automatically deallocated by Tcl_FinalizeThread.
198
200 All of these synchronization objects are self initializing. They are
201 implemented as opaque pointers that should be NULL upon first use. The
202 mutexes and condition variables are either cleaned up by process exit │
203 handlers (if living that long) or explicitly by calls to Tcl_MutexFi‐ │
204 nalize or Tcl_ConditionFinalize. Thread local storage is reclaimed
205 during Tcl_FinalizeThread.
206
208 The API to create threads is not finalized at this time. There are
209 private facilities to create threads that contain a new Tcl inter‐
210 preter, and to send scripts among threads. Dive into tclThreadTest.c
211 and tclThread.c for examples.
212
214 Tcl_GetCurrentThread, Tcl_ThreadQueueEvent, Tcl_ThreadAlert, Tcl_Exit‐
215 Thread, Tcl_FinalizeThread, Tcl_CreateThreadExitHandler,
216 Tcl_DeleteThreadExitHandler
217
219 thread, mutex, condition variable, thread local storage
220Tcl 8.1 Threads(3)