1. QCamera2基础组件——cam_semaphore

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#ifndef __QCAMERA_SEMAPHORE_H__
#define __QCAMERA_SEMAPHORE_H__

#ifdef __cplusplus
extern "C" {
#endif

/* Implement semaphore with mutex and conditional variable.
 * Reason being, POSIX semaphore on Android are not used or
 * well tested.
 */

/*
 * 一个非常简单的信号机制，用于进行线程同步。
 * 从 val 进行同步的信号量，mutex 和 cond 用来实现 同步信号量val 的保护.
*/

typedef struct {
    int val;
    pthread_mutex_t mutex;
    pthread_cond_t cond;
} cam_semaphore_t;

static inline void cam_sem_init(cam_semaphore_t *s, int n)
{
    pthread_mutex_init(&(s->mutex), NULL);
    pthread_cond_init(&(s->cond), NULL);
    s->val = n;   // 通常 n = 0
}

static inline void cam_sem_post(cam_semaphore_t *s)
{
    pthread_mutex_lock(&(s->mutex));
    s->val++;
    pthread_cond_signal(&(s->cond));
    pthread_mutex_unlock(&(s->mutex));
}

static inline int cam_sem_wait(cam_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;
}

static inline void cam_sem_destroy(cam_semaphore_t *s)
{
    pthread_mutex_destroy(&(s->mutex));
    pthread_cond_destroy(&(s->cond));
    s->val = 0;
}

#ifdef __cplusplus
}
#endif

#endif /* __QCAMERA_SEMAPHORE_H__ */