SDL_syssem.c File Reference

#include "../../SDL_internal.h"
#include "SDL_timer.h"
#include "SDL_thread.h"
#include "SDL_systhread_c.h"

Include dependency graph for SDL_syssem.c:

Go to the source code of this file.

Data Structures
struct	SDL_sem

Functions
SDL_sem *	SDL_CreateSemaphore (Uint32 initial_value)
void	SDL_DestroySemaphore (SDL_sem *sem)
int	SDL_SemTryWait (SDL_sem *sem)
int	SDL_SemWaitTimeout (SDL_sem *sem, Uint32 timeout)
int	SDL_SemWait (SDL_sem *sem)
Uint32	SDL_SemValue (SDL_sem *sem)
int	SDL_SemPost (SDL_sem *sem)

Function Documentation

SDL_CreateSemaphore()

SDL_sem* SDL_CreateSemaphore

(

Uint32

initial_value

)

Create a semaphore, initialized with value, returns NULL on failure.

Definition at line 85 of file SDL_syssem.c.

{
    SDL_sem *sem;
 
    sem = (SDL_sem *) SDL_malloc(sizeof(*sem));
    if (!sem) {
        SDL_OutOfMemory();
        return NULL;
    }
    sem->count = initial_value;
    sem->waiters_count = 0;
 
    sem->count_lock = SDL_CreateMutex();
    sem->count_nonzero = SDL_CreateCond();
    if (!sem->count_lock || !sem->count_nonzero) {
        SDL_DestroySemaphore(sem);
        return NULL;
    }
 
    return sem;
}

SDL_DestroySemaphore()

void SDL_DestroySemaphore

(

SDL_sem *

sem

)

Destroy a semaphore.

Definition at line 111 of file SDL_syssem.c.

{
    if (sem) {
        sem->count = 0xFFFFFFFF;
        while (sem->waiters_count > 0) {
            SDL_CondSignal(sem->count_nonzero);
            SDL_Delay(10);
        }
        SDL_DestroyCond(sem->count_nonzero);
        if (sem->count_lock) {
            SDL_LockMutex(sem->count_lock);
            SDL_UnlockMutex(sem->count_lock);
            SDL_DestroyMutex(sem->count_lock);
        }
        SDL_free(sem);
    }
}

Referenced by SDL_CreateSemaphore().

SDL_SemPost()

int SDL_SemPost

(

SDL_sem *

sem

)

Atomically increases the semaphore's count (not blocking).

Returns

0, or -1 on error.

Definition at line 200 of file SDL_syssem.c.

{
    if (!sem) {
        return SDL_SetError("Passed a NULL semaphore");
    }
 
    SDL_LockMutex(sem->count_lock);
    if (sem->waiters_count > 0) {
        SDL_CondSignal(sem->count_nonzero);
    }
    ++sem->count;
    SDL_UnlockMutex(sem->count_lock);
 
    return 0;
}

SDL_SemTryWait()

int SDL_SemTryWait

(

SDL_sem *

sem

)

Non-blocking variant of SDL_SemWait().

Returns

0 if the wait succeeds, SDL_MUTEX_TIMEDOUT if the wait would block, and -1 on error.

Definition at line 130 of file SDL_syssem.c.

{
    int retval;
 
    if (!sem) {
        return SDL_SetError("Passed a NULL semaphore");
    }
 
    retval = SDL_MUTEX_TIMEDOUT;
    SDL_LockMutex(sem->count_lock);
    if (sem->count > 0) {
        --sem->count;
        retval = 0;
    }
    SDL_UnlockMutex(sem->count_lock);
 
    return retval;
}

Referenced by SDL_SemWaitTimeout().

SDL_SemValue()

Uint32 SDL_SemValue

(

SDL_sem *

sem

)

Returns the current count of the semaphore.

Definition at line 186 of file SDL_syssem.c.

{
    Uint32 value;
 
    value = 0;
    if (sem) {
        SDL_LockMutex(sem->count_lock);
        value = sem->count;
        SDL_UnlockMutex(sem->count_lock);
    }
    return value;
}

SDL_SemWait()

int SDL_SemWait

(

SDL_sem *

sem

)

This function suspends the calling thread until the semaphore pointed to by sem has a positive count. It then atomically decreases the semaphore count.

Definition at line 180 of file SDL_syssem.c.

{
    return SDL_SemWaitTimeout(sem, SDL_MUTEX_MAXWAIT);
}

Referenced by SDL_SemWaitTimeout().

SDL_SemWaitTimeout()

int SDL_SemWaitTimeout	(	SDL_sem *	sem,
		Uint32	ms
	)

Variant of SDL_SemWait() with a timeout in milliseconds.

Returns

0 if the wait succeeds, SDL_MUTEX_TIMEDOUT if the wait does not succeed in the allotted time, and -1 on error.

Warning

On some platforms this function is implemented by looping with a delay of 1 ms, and so should be avoided if possible.

Definition at line 150 of file SDL_syssem.c.

{
    int retval;
 
    if (!sem) {
        return SDL_SetError("Passed a NULL semaphore");
    }
 
    /* A timeout of 0 is an easy case */
    if (timeout == 0) {
        return SDL_SemTryWait(sem);
    }
 
    SDL_LockMutex(sem->count_lock);
    ++sem->waiters_count;
    retval = 0;
    while ((sem->count == 0) && (retval != SDL_MUTEX_TIMEDOUT)) {
        retval = SDL_CondWaitTimeout(sem->count_nonzero,
                                     sem->count_lock, timeout);
    }
    --sem->waiters_count;
    if (retval == 0) {
        --sem->count;
    }
    SDL_UnlockMutex(sem->count_lock);
 
    return retval;
}

Referenced by SDL_SemWait().