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Diffstat (limited to 'generic/tclThreadJoin.c')
| -rw-r--r-- | generic/tclThreadJoin.c | 316 |
1 files changed, 316 insertions, 0 deletions
diff --git a/generic/tclThreadJoin.c b/generic/tclThreadJoin.c new file mode 100644 index 0000000..5c70a62 --- /dev/null +++ b/generic/tclThreadJoin.c @@ -0,0 +1,316 @@ +/* + * tclThreadJoin.c -- + * + * This file implements a platform independent emulation layer for the + * handling of joinable threads. The Windows platform uses this code to + * provide the functionality of joining threads. This code is currently + * not necessary on Unix. + * + * Copyright (c) 2000 by Scriptics Corporation + * + * See the file "license.terms" for information on usage and redistribution of + * this file, and for a DISCLAIMER OF ALL WARRANTIES. + */ + +#include "tclInt.h" + +#ifdef _WIN32 + +/* + * The information about each joinable thread is remembered in a structure as + * defined below. + */ + +typedef struct JoinableThread { + Tcl_ThreadId id; /* The id of the joinable thread. */ + int result; /* A place for the result after the demise of + * the thread. */ + int done; /* Boolean flag. Initialized to 0 and set to 1 + * after the exit of the thread. This allows a + * thread requesting a join to detect when + * waiting is not necessary. */ + int waitedUpon; /* Boolean flag. Initialized to 0 and set to 1 + * by the thread waiting for this one via + * Tcl_JoinThread. Used to lock any other + * thread trying to wait on this one. */ + Tcl_Mutex threadMutex; /* The mutex used to serialize access to this + * structure. */ + Tcl_Condition cond; /* This is the condition a thread has to wait + * upon to get notified of the end of the + * described thread. It is signaled indirectly + * by Tcl_ExitThread. */ + struct JoinableThread *nextThreadPtr; + /* Reference to the next thread in the list of + * joinable threads. */ +} JoinableThread; + +/* + * The following variable is used to maintain the global list of all joinable + * threads. Usage by a thread is allowed only if the thread acquired the + * 'joinMutex'. + */ + +TCL_DECLARE_MUTEX(joinMutex) + +static JoinableThread *firstThreadPtr; + +/* + *---------------------------------------------------------------------- + * + * TclJoinThread -- + * + * This procedure waits for the exit of the thread with the specified id + * and returns its result. + * + * Results: + * A standard tcl result signaling the overall success/failure of the + * operation and an integer result delivered by the thread which was + * waited upon. + * + * Side effects: + * Deallocates the memory allocated by TclRememberJoinableThread. + * Removes the data associated to the thread waited upon from the list of + * joinable threads. + * + *---------------------------------------------------------------------- + */ + +int +TclJoinThread( + Tcl_ThreadId id, /* The id of the thread to wait upon. */ + int *result) /* Reference to a location for the result of + * the thread we are waiting upon. */ +{ + JoinableThread *threadPtr; + + /* + * Steps done here: + * i. Acquire the joinMutex and search for the thread. + * ii. Error out if it could not be found. + * iii. If found, switch from exclusive access to the list to exclusive + * access to the thread structure. + * iv. Error out if some other is already waiting. + * v. Skip the waiting part of the thread is already done. + * vi. Wait for the thread to exit, mark it as waited upon too. + * vii. Get the result form the structure, + * viii. switch to exclusive access of the list, + * ix. remove the structure from the list, + * x. then switch back to exclusive access to the structure + * xi. and delete it. + */ + + Tcl_MutexLock(&joinMutex); + + threadPtr = firstThreadPtr; + while (threadPtr!=NULL && threadPtr->id!=id) { + threadPtr = threadPtr->nextThreadPtr; + } + + if (threadPtr == NULL) { + /* + * Thread not found. Either not joinable, or already waited upon and + * exited. Whatever, an error is in order. + */ + + Tcl_MutexUnlock(&joinMutex); + return TCL_ERROR; + } + + /* + * [1] If we don't lock the structure before giving up exclusive access to + * the list some other thread just completing its wait on the same thread + * can delete the structure from under us, leaving us with a dangling + * pointer. + */ + + Tcl_MutexLock(&threadPtr->threadMutex); + Tcl_MutexUnlock(&joinMutex); + + /* + * [2] Now that we have the structure mutex any other thread that just + * tries to delete structure will wait at location [3] until we are done + * with the structure. And in that case we are done with it rather quickly + * as 'waitedUpon' will be set and we will have to error out. + */ + + if (threadPtr->waitedUpon) { + Tcl_MutexUnlock(&threadPtr->threadMutex); + return TCL_ERROR; + } + + /* + * We are waiting now, let other threads recognize this. + */ + + threadPtr->waitedUpon = 1; + + while (!threadPtr->done) { + Tcl_ConditionWait(&threadPtr->cond, &threadPtr->threadMutex, NULL); + } + + /* + * We have to release the structure before trying to access the list again + * or we can run into deadlock with a thread at [1] (see above) because of + * us holding the structure and the other holding the list. There is no + * problem with dangling pointers here as 'waitedUpon == 1' is still valid + * and any other thread will error out and not come to this place. IOW, + * the fact that we are here also means that no other thread came here + * before us and is able to delete the structure. + */ + + Tcl_MutexUnlock(&threadPtr->threadMutex); + Tcl_MutexLock(&joinMutex); + + /* + * We have to search the list again as its structure may (may, almost + * certainly) have changed while we were waiting. Especially now is the + * time to compute the predecessor in the list. Any earlier result can be + * dangling by now. + */ + + if (firstThreadPtr == threadPtr) { + firstThreadPtr = threadPtr->nextThreadPtr; + } else { + JoinableThread *prevThreadPtr = firstThreadPtr; + + while (prevThreadPtr->nextThreadPtr != threadPtr) { + prevThreadPtr = prevThreadPtr->nextThreadPtr; + } + prevThreadPtr->nextThreadPtr = threadPtr->nextThreadPtr; + } + + Tcl_MutexUnlock(&joinMutex); + + /* + * [3] Now that the structure is not part of the list anymore no other + * thread can acquire its mutex from now on. But it is possible that + * another thread is still holding the mutex though, see location [2]. So + * we have to acquire the mutex one more time to wait for that thread to + * finish. We can (and have to) release the mutex immediately. + */ + + Tcl_MutexLock(&threadPtr->threadMutex); + Tcl_MutexUnlock(&threadPtr->threadMutex); + + /* + * Copy the result to us, finalize the synchronisation objects, then free + * the structure and return. + */ + + *result = threadPtr->result; + + Tcl_ConditionFinalize(&threadPtr->cond); + Tcl_MutexFinalize(&threadPtr->threadMutex); + ckfree(threadPtr); + + return TCL_OK; +} + +/* + *---------------------------------------------------------------------- + * + * TclRememberJoinableThread -- + * + * This procedure remebers a thread as joinable. Only a call to + * TclJoinThread will remove the structre created (and initialized) here. + * IOW, not waiting upon a joinable thread will cause memory leaks. + * + * Results: + * None. + * + * Side effects: + * Allocates memory, adds it to the global list of all joinable threads. + * + *---------------------------------------------------------------------- + */ + +void +TclRememberJoinableThread( + Tcl_ThreadId id) /* The thread to remember as joinable */ +{ + JoinableThread *threadPtr; + + threadPtr = ckalloc(sizeof(JoinableThread)); + threadPtr->id = id; + threadPtr->done = 0; + threadPtr->waitedUpon = 0; + threadPtr->threadMutex = (Tcl_Mutex) NULL; + threadPtr->cond = (Tcl_Condition) NULL; + + Tcl_MutexLock(&joinMutex); + + threadPtr->nextThreadPtr = firstThreadPtr; + firstThreadPtr = threadPtr; + + Tcl_MutexUnlock(&joinMutex); +} + +/* + *---------------------------------------------------------------------- + * + * TclSignalExitThread -- + * + * This procedure signals that the specified thread is done with its + * work. If the thread is joinable this signal is propagated to the + * thread waiting upon it. + * + * Results: + * None. + * + * Side effects: + * Modifies the associated structure to hold the result. + * + *---------------------------------------------------------------------- + */ + +void +TclSignalExitThread( + Tcl_ThreadId id, /* Id of the thread signaling its exit. */ + int result) /* The result from the thread. */ +{ + JoinableThread *threadPtr; + + Tcl_MutexLock(&joinMutex); + + threadPtr = firstThreadPtr; + while ((threadPtr != NULL) && (threadPtr->id != id)) { + threadPtr = threadPtr->nextThreadPtr; + } + + if (threadPtr == NULL) { + /* + * Thread not found. Not joinable. No problem, nothing to do. + */ + + Tcl_MutexUnlock(&joinMutex); + return; + } + + /* + * Switch over the exclusive access from the list to the structure, then + * store the result, set the flag and notify the waiting thread, provided + * that it exists. The order of lock/unlock ensures that a thread entering + * 'TclJoinThread' will not interfere with us. + */ + + Tcl_MutexLock(&threadPtr->threadMutex); + Tcl_MutexUnlock(&joinMutex); + + threadPtr->done = 1; + threadPtr->result = result; + + if (threadPtr->waitedUpon) { + Tcl_ConditionNotify(&threadPtr->cond); + } + + Tcl_MutexUnlock(&threadPtr->threadMutex); +} +#endif /* _WIN32 */ + +/* + * Local Variables: + * mode: c + * c-basic-offset: 4 + * fill-column: 78 + * End: + */ |