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Allegro 4.9 includes a simple cross-platform threading interface. It is a thin layer on top of two threading APIs: Windows threads and POSIX Threads (pthreads). Enforcing a consistent semantics on all platforms would be difficult at best, hence the behaviour of the following functions will differ subtly on different platforms (more so than usual). Your best bet is to be aware of this and code to the intersection of the semantics and avoid edge cases. These functions are declared in the main Allegro header file:
ALLEGRO_THREAD
An opaque structure representing a thread. ALLEGRO_COND
An opaque structure representing a condition variable. al_create_thread
Spawn a new thread which begins executing Returns true if the thread was created, false if there was an error. See also: al_start_thread, al_join_thread. al_start_thread
When a thread is created, it is initially in a suspended state. Calling al_start_thread will start its actual execution. Starting a thread which has already been started does nothing. See also: al_create_thread. al_join_thread
Wait for the thread to finish executing. This implicitly calls al_set_thread_should_stop first. If See also: al_set_thread_should_stop, al_get_thread_should_stop, al_destroy_thread. al_set_thread_should_stop
Set the flag to indicate See also: al_join_thread, al_get_thread_should_stop. al_get_thread_should_stop
Check if another thread is waiting for Returns true if another thread has called al_join_thread or al_set_thread_should_stop on this thread. See also: al_join_thread, al_set_thread_should_stop. Note: We don't support forceful killing of threads. al_destroy_thread
Free the resources used by a thread. Implicitly performs al_join_thread on the thread if it hasn't been done already. Does nothing if See also: al_join_thread. al_run_detached_thread
Runs the passed function in its own thread, with al_create_mutex
Create the mutex object (a mutual exclusion device). The mutex may or may not support "recursive" locking. Returns the mutex on success or See also: al_create_mutex_recursive. al_create_mutex_recursive
Create the mutex object (a mutual exclusion device), with support for "recursive" locking. That is, the mutex will count the number of times it has been locked by the same thread. If the caller tries to acquire a lock on the mutex when it already holds the lock then the count is incremented. The mutex is only unlocked when the thread releases the lock on the mutex an equal number of times, i.e. the count drops down to zero. See also: al_create_mutex. al_lock_mutex
Acquire the lock on If the mutex is already locked by the calling thread, then the behaviour depends on whether the mutex was created with al_create_mutex or al_create_mutex_recursive. In the former case, the behaviour is undefined; the most likely behaviour is deadlock. In the latter case, the count in the mutex will be incremented and the call will return immediately. See also: al_unlock_mutex. We don't yet have al_mutex_trylock. al_unlock_mutex
Release the lock on If the calling thread doesn't hold the lock, or if the mutex is not locked, undefined behaviour results. See also: al_lock_mutex. al_destroy_mutex
Free the resources used by the mutex. The mutex should be unlocked. Destroying a locked mutex results in undefined behaviour. Does nothing if al_create_cond
Create a condition variable. Returns the condition value on success or al_destroy_cond
Destroy a condition variable. Destroying a condition variable which has threads block on it results in undefined behaviour. Does nothing if al_wait_cond
On entering this function, Example of proper use:
The mutex should be locked before checking the condition, and should be rechecked al_wait_cond returns. al_wait_cond can return for other reasons than the condition becoming true (e.g. the process was signalled). If multiple threads are blocked on the condition variable, the condition may no longer be true by the time the second and later threads are unblocked. Remember not to unlock the mutex prematurely. See also: al_wait_cond_timed, al_broadcast_cond, al_signal_cond. al_wait_cond_timed
Like al_wait_cond but the call can return if the absolute time passes Returns zero on success, non-zero if the call timed out. Fix up the return value. pthread_cond_timedwait returns ETIMEDOUT but can return other errors. Do we need to return other errors? al_broadcast_cond
Unblock all threads currently waiting on a condition variable. That is, broadcast that some condition which those threads were waiting for has become true. See also: al_signal_cond. Note: The pthreads spec says to lock the mutex associated with al_signal_cond
Unblock at least one thread waiting on a condition variable. Generally you should use al_broadcast_cond but al_signal_cond may be more efficient when it's applicable. See also: al_broadcast_cond. |
Last updated: 2010-05-26 10:53:31 UTC