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| Deletions are marked like this. | Additions are marked like this. |
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| #pragma disable-camelcase ||<tablewidth="100%" style="color: #FF0000;" :> DRAFT|| |
#pragma camelcase off |
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| Use this function to suspend the calling thread until the semaphore pointed to by '''sem''' has a positive count, then atomically decrease the semaphore count ''-or-'' ^...suspend the calling thread until the semaphore can be atomically decremented^ ''-or-'' *lock a semaphore and suspend the thread if the semaphore value is zero*. | Use this function wait until a semaphore has a positive value and then decrements it. |
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| ||'''sem'''||^the semaphore to monitor^|| | ||'''sem'''||the semaphore wait on|| |
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| If the semaphore was not successfully locked, the semaphore will be unchanged. ??? |
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| * {{{#!highlight cpp if (SDL_SemWait(my_sem) == -1) { return WAIT_FAILED; } ... SDL_SemPost(my_sem); }}} * |
<<Include(SDL_CreateSemaphore, , , from="## Begin Semaphore Example", to="## End Semaphore Example")>> |
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| *<<BR>>[[SDL_SemWait]]() suspends the calling thread until either the semaphore pointed to by '''sem''' has a positive value or the call is interrupted by a signal or error. If the call is successful it will atomically decrement the semaphore value. | This function suspends the calling thread until either the semaphore pointed to by '''sem''' has a positive value or the call is interrupted by a signal or error. If the call is successful it will atomically decrement the semaphore value. |
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| After [[SDL_SemWait]]() is successful, the semaphore can be released and its count atomically incremented by a successful call to [[SDL_SemPost]](). <<BR>>* <<Color2(green,Should the Remarks include any discussion of locking and unlocking for clarity? For example is the lock/unlock pair a built-in feature of this function or does the programmer have to 'manually' lock then unlock the semaphore or thread when using this function? Would it be beneficial to a user to have some discussion of that here or is it just understood/given?)>> |
This function is the equivalent of calling [[SDL_SemWaitTimeout]]() with a time length of SDL_MUTEX_MAXWAIT. |
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| .[[SDL_SemPost]] * .[[SDL_SemTryWait]] * .[[SDL_SemValue]] * .[[SDL_SemWaitTimeout]] * |
.[[SDL_CreateSemaphore]] .[[SDL_DestroySemaphore]] .[[SDL_SemPost]] .[[SDL_SemTryWait]] .[[SDL_SemValue]] .[[SDL_SemWait]] .[[SDL_SemWaitTimeout]] |
SDL_SemWait
Use this function wait until a semaphore has a positive value and then decrements it.
Contents
Syntax
int SDL_SemWait(SDL_sem* sem)
Function Parameters
sem |
the semaphore wait on |
Return Value
Returns 0 on success or a negative error code on failure; call SDL_GetError() for more information.
Code Examples
Typical use of semaphores:
SDL_atomic_t done;
SDL_sem *sem;
SDL_AtomicSet(&done, 0);
sem = SDL_CreateSemaphore(0);
.
.
Thread A:
while (!SDL_AtomicGet(&done)) {
add_data_to_queue();
SDL_SemPost(sem);
}
Thread B:
while (!SDL_AtomicGet(&done)) {
SDL_SemWait(sem);
if (data_available()) {
get_data_from_queue();
}
}
.
.
SDL_AtomicSet(&done, 1);
SDL_SemPost(sem);
wait_for_threads();
SDL_DestroySemaphore(sem);
Remarks
This function suspends the calling thread until either the semaphore pointed to by sem has a positive value or the call is interrupted by a signal or error. If the call is successful it will atomically decrement the semaphore value.
This function is the equivalent of calling SDL_SemWaitTimeout() with a time length of SDL_MUTEX_MAXWAIT.
