多线程 - 使用Mutex和条件变量实现信号量

说明

在某些平台，信号量可能并不支持，可以使用互斥锁和条件变量模拟实现信号量，代码如下

代码

typedef struct {
    int val;	//信号量的值
    pthread_mutex_t mutex;
    pthread_cond_t cond;
} semaphore_t;

inline void sem_init(semaphore_t *s, int n)
{
    pthread_mutex_init(&(s->mutex), NULL);
    pthread_cond_init(&(s->cond), NULL);
    s->val = n;
}

inline void sem_post(semaphore_t *s)
{
    pthread_mutex_lock(&(s->mutex));
    s->val++;
    pthread_cond_signal(&(s->cond));
    pthread_mutex_unlock(&(s->mutex));
}

inline int sem_wait(semaphore_t *s)
{
    int rc = 0;
    pthread_mutex_lock(&(s->mutex));
    while (s->val == 0)
        rc = pthread_cond_wait(&(s->cond), &(s->mutex));
    s->val--;
    pthread_mutex_unlock(&(s->mutex));
    return rc;
}

inline void sem_destroy(semaphore_t *s)
{
    pthread_mutex_destroy(&(s->mutex));
    pthread_cond_destroy(&(s->cond));
    s->val = 0;
}