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AG_THREADS(3) Library Functions Manual AG_THREADS(3) NAME AG_Threads -- agar threads support SYNOPSIS #include <agar/core.h> DESCRIPTION On platforms with threads support, Agar can be compiled with support for multithreading. In a threaded build, Agar API calls can be consid- ered free-threaded (safe to use from different threads without need for application-level synchronization) unless documented otherwise. Even though calls are free-threaded, application-level synchronization (calls to AG_ObjectLock(3)) may still be needed in some cases. See "EXAMPLES" for some examples of thread-unsafe vs. thread-safe usages. CONVENTIONS Agar function calls are free-threaded unless mentioned otherwise. The AG_Object(3) system provides a per-object recursive mutex which is implicitely acquired before invoking object methods or processing events. THREADS INTERFACE When compiled with threads support, Agar provides a portable, minimal interface to the operating system's native threads interface. These functions follow Agar's standard error-handling style (see AG_Intro(3)). MUTEXES Mutexes (MUTual EXclusion devices) are commonly used to protect shared data structure against concurrent modifications. void AG_MutexInit(AG_Mutex *mutex) int AG_MutexTryInit(AG_Mutex *mutex) void AG_MutexInitRecursive(AG_Mutex *mutex) int AG_MutexTryInitRecursive(AG_Mutex *mutex) void AG_MutexDestroy(AG_Mutex *mutex) void AG_MutexLock(AG_Mutex *mutex) int AG_MutexTryLock(AG_Mutex *mutex) void AG_MutexUnlock(AG_Mutex *mutex) The AG_MutexInit() function initializes a mutex structure. AG_MutexInitRecursive() initializes a recursive mutex (a mutex with a reference count), which allows nested AG_MutexLock() calls. AG_MutexDestroy() frees all resources allocated for a mutex. AG_MutexLock() and AG_MutexUnlock() respectively acquire and release a mutex. AG_MutexTryLock() tries to acquire a mutex without blocking and immedi- ately returns 0 on success. On failure, the function returns -1, but does not set any error message (so AG_GetError(3) should not be used). CONDITION VARIABLES void AG_CondInit(AG_Cond *cv) int AG_CondTryInit(AG_Cond *cv) void AG_CondDestroy(AG_Cond *cv) void AG_CondBroadcast(AG_Cond *cv) void AG_CondSignal(AG_Cond *cv) int AG_CondWait(AG_Cond *cv, AG_Mutex *m) int AG_CondTimedWait(AG_Cond *cv, AG_Mutex *m, const struct timespec *t) AG_CondInit() initializes a condition variable structure. AG_CondDestroy() releases resources allocated for a condition variable. AG_CondBroadcast() unblock all threads which are currently blocked waiting on cv. AG_CondSignal() unblocks at least one thread currently blocked waiting on cv. AG_CondWait() blocks the calling thread until cv is signaled. The AG_CondTimedWait() variant will not block for more than the specified amount of time. All of these functions will raise a fatal condition if an error is en- countered. THREADS void AG_ThreadCreate(AG_Thread *th, void *(*fn)(void *arg), void *arg) int AG_ThreadTryCreate(AG_Thread *th, void *(*fn)(void *arg), void *arg) void AG_ThreadCancel(AG_Thread th) int AG_ThreadTryCancel(AG_Thread th) void AG_ThreadJoin(AG_Thread th, void **exitVal) int AG_ThreadTryJoin(AG_Thread th, void **exitVal) void AG_ThreadExit(void *exitVal) void AG_ThreadKill(AG_Thread th, int signal) AG_Thread AG_ThreadSelf(void) int AG_ThreadEqual(AG_Thread a, AG_Thread b) AG_ThreadCreate() creates a new thread executing fn. The optional ar- gument arg is passed to fn. The AG_ThreadCancel() routine requests that the specified thread be cancelled. If the given thread is invalid, a fatal error is raised. The AG_ThreadJoin() function suspends the execution of the current thread until th terminates. When it does, the value passed to AG_ThreadExit() is made available in exitVal. AG_ThreadExit() terminates the current thread. exitVal is an optional user pointer. AG_ThreadKill() sends a signal to the specified thread. AG_ThreadSelf() returns the identifier of the current (caller's) thread. AG_ThreadEqual() returns 1 if the identifiers a and b both re- fer to the same thread, or 0 if they differ. THREAD-SPECIFIC VARIABLES void AG_ThreadKeyCreate(AG_ThreadKey *key, void (*destructor)(void *)) int AG_ThreadKeyTryCreate(AG_ThreadKey *key, void (*destructor)(void *)) void AG_ThreadKeyDelete(AG_ThreadKey key) int AG_ThreadKeyTryDelete(AG_ThreadKey key) void * AG_ThreadKeyGet(AG_ThreadKey key) void AG_ThreadKeySet(AG_ThreadKey key, const void *value) int AG_ThreadKeyTrySet(AG_ThreadKey key, const void *value) AG_ThreadKeyCreate() initializes a key (i.e., a handle) to a thread- specific value. The handle itself is accessible to all threads. The thread-specific value (i.e., the value specified by AG_ThreadKeySet(), and which defaults to NULL) will persist only for the life of the thread. If an optional destructor is given, that function will be called (with the thread-specific value as its argument), when the thread exists. The AG_ThreadKeyDelete() function releases resources allocated for a key. AG_ThreadKeyGet() returns the thread-specific value associated with key. AG_ThreadKeySet() sets a thread-specific value with key. EXAMPLES The following code uses the return value of a VFS lookup in a manner which is not thread-safe. A race condition exists between the AG_ObjectFind() call and the following access: AG_Object *o; o = AG_ObjectFind(root, "/Foo"); if (o != NULL) { /* ... */ } /* UNSAFE access */ The following code accesses the returned object safely by acquiring the mutex of the VFS root object (which protects the entire VFS linkage): AG_Object *o; AG_ObjectLock(root); o = AG_ObjectFind(root, "/Foo"); if (o != NULL) { /* ... */ } /* Safe access */ AG_ObjectUnlock(root); SEE ALSO AG_Intro(3), AG_Object(3) HISTORY The AG_Threads interface first appeared in Agar 1.0 Agar 1.7 December 21, 2022 AG_THREADS(3)
NAME | SYNOPSIS | DESCRIPTION | CONVENTIONS | THREADS INTERFACE | MUTEXES | CONDITION VARIABLES | THREADS | THREAD-SPECIFIC VARIABLES | EXAMPLES | SEE ALSO | HISTORY
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