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,
44 which must be associated
45 with a mutex lock.
46 Tcl_Mutex *mutexPtr (in) A mutex lock.
48 Tcl_Time *timePtr (in) A time limit on the con‐
50 dition wait. NULL to
51 wait forever. Note that
52 a polling value of 0 sec‐
53 onds does not make much
54 sense.
55 Tcl_ThreadDataKey *keyPtr (in) This identifies a block
57 of thread local storage.
58 The key should be static
59 and process-wide, yet
60 each thread will end up
61 associating a different
62 block of storage with
63 this key.
64 int *size (in) The size of the thread
66 local storage block.
67 This amount of data is
68 allocated and initialized
69 to zero the first time
70 each thread calls
71 Tcl_GetThreadData.
72 Tcl_ThreadId *idPtr (out) The referred storage will
74 contain the id of the
75 newly created thread as
76 returned by the operating
77 system.
78 Tcl_ThreadId id (in) Id of the thread waited
80 upon.
81 Tcl_ThreadCreateProc threadProc (in) This procedure will act
83 as the main() of the
84 newly created thread. The
85 specified clientData will
86 be its sole argument.
87 ClientData clientData (in) Arbitrary information.
89 Passed as sole argument
90 to the threadProc.
91 int stackSize (in) The size of the stack
93 given to the new thread.
94 int flags (in) Bitmask containing flags
96 allowing the caller to
97 modify behaviour of the
98 new thread.
99 int *result (out) The referred storage is
101 used to place the exit
102 code of the thread waited
103 upon into it.
104_________________________________________________________________
105
107 Beginning with the 8.1 release, the Tcl core is thread safe, which
108 allows you to incorporate Tcl into multithreaded applications without
109 customizing the Tcl core. To enable Tcl multithreading support, you
110 must include the --enable-threads option to configure when you config‐
111 ure and compile your Tcl core.
112 An important constraint of the Tcl threads implementation is that only
114 the thread that created a Tcl interpreter can use that interpreter. In
115 other words, multiple threads can not access the same Tcl interpreter.
116 (However, a single thread can safely create and use multiple inter‐
117 preters.)
118
120 Tcl provides Tcl_CreateThread for creating threads. The caller can
121 determine the size of the stack given to the new thread and modify the
122 behaviour through the supplied flags. The value
123 TCL_THREAD_STACK_DEFAULT for the stackSize indicates that the default
124 size as specified by the operating system is to be used for the new
125 thread. As for the flags, currently only the values TCL_THREAD_NOFLAGS
126 and TCL_THREAD_JOINABLE are defined. The first of them invokes the
127 default behaviour with no specialties. Using the second value marks the
128 new thread as joinable. This means that another thread can wait for the
129 such marked thread to exit and join it.
130 Restrictions: On some UNIX systems the pthread-library does not contain
132 the functionality to specify the stack size of a thread. The specified
133 value for the stack size is ignored on these systems. Windows cur‐
134 rently does not support joinable threads. This flag value is therefore
135 ignored on this platform.
136 Tcl provides the Tcl_ExitThread and Tcl_FinalizeThread functions for
138 terminating threads and invoking optional per-thread exit handlers.
139 See the Tcl_Exit page for more information on these procedures.
140 The Tcl_JoinThread function is provided to allow threads to wait upon
142 the exit of another thread, which must have been marked as joinable
143 through usage of the TCL_THREAD_JOINABLE-flag during its creation via
144 Tcl_CreateThread.
145 Trying to wait for the exit of a non-joinable thread or a thread which
147 is already waited upon will result in an error. Waiting for a joinable
148 thread which already exited is possible, the system will retain the
149 necessary information until after the call to Tcl_JoinThread. This
150 means that not calling Tcl_JoinThread for a joinable thread will cause
151 a memory leak.
152 The Tcl_GetThreadData call returns a pointer to a block of thread-pri‐
154 vate data. Its argument is a key that is shared by all threads and a
155 size for the block of storage. The storage is automatically allocated
156 and initialized to all zeros the first time each thread asks for it.
157 The storage is automatically deallocated by Tcl_FinalizeThread.
158 SYNCHRONIZATION AND COMMUNICATION
160 Tcl provides Tcl_ThreadQueueEvent and Tcl_ThreadAlert for handling
161 event queuing in multithreaded applications. See the Notifier manual
162 page for more information on these procedures.
163 A mutex is a lock that is used to serialize all threads through a piece
165 of code by calling Tcl_MutexLock and Tcl_MutexUnlock. If one thread
166 holds a mutex, any other thread calling Tcl_MutexLock will block until
167 Tcl_MutexUnlock is called. A mutex can be destroyed after its use by
168 calling Tcl_MutexFinalize. The result of locking a mutex twice from
169 the same thread is undefined. On some platforms it will result in a
170 deadlock. The Tcl_MutexLock, Tcl_MutexUnlock and Tcl_MutexFinalize
171 procedures are defined as empty macros if not compiling with threads
172 enabled. For declaration of mutexes the TCL_DECLARE_MUTEX macro should
173 be used. This macro assures correct mutex handling even when the core
174 is compiled without threads enabled.
175 A condition variable is used as a signaling mechanism: a thread can
177 lock a mutex and then wait on a condition variable with Tcl_Condition‐
178 Wait. This atomically releases the mutex lock and blocks the waiting
179 thread until another thread calls Tcl_ConditionNotify. The caller of
180 Tcl_ConditionNotify should have the associated mutex held by previously
181 calling Tcl_MutexLock, but this is not enforced. Notifying the condi‐
182 tion variable unblocks all threads waiting on the condition variable,
183 but they do not proceed until the mutex is released with Tcl_MutexUn‐
184 lock. The implementation of Tcl_ConditionWait automatically locks the
185 mutex before returning.
186 The caller of Tcl_ConditionWait should be prepared for spurious notifi‐
188 cations by calling Tcl_ConditionWait within a while loop that tests
189 some invariant.
190 A condition variable can be destroyed after its use by calling Tcl_Con‐
192 ditionFinalize.
193 The Tcl_ConditionNotify, Tcl_ConditionWait and Tcl_ConditionFinalize
195 procedures are defined as empty macros if not compiling with threads
196 enabled.
197 INITIALIZATION
199 All of these synchronization objects are self-initializing. They are
200 implemented as opaque pointers that should be NULL upon first use. The
201 mutexes and condition variables are either cleaned up by process exit
202 handlers (if living that long) or explicitly by calls to Tcl_MutexFi‐
203 nalize or Tcl_ConditionFinalize. Thread local storage is reclaimed
204 during Tcl_FinalizeThread.
205
207 Tcl provides no built-in commands for scripts to use to create, manage, │
208 or join threads, nor any script-level access to mutex or condition │
209 variables. It provides such facilities only via C interfaces, and │
210 leaves it up to packages to expose these matters to the script level. │
211 One such package is the Thread package.
212
214 Tcl_GetCurrentThread(3), Tcl_ThreadQueueEvent(3), Tcl_ThreadAlert(3),
215 Tcl_ExitThread(3), Tcl_FinalizeThread(3), Tcl_CreateThreadEx‐
216 itHandler(3), Tcl_DeleteThreadExitHandler(3), Thread
217
219 thread, mutex, condition variable, thread local storage
220Tcl 8.1 Threads(3)