用C语言实现一个超时锁

超时锁是一种常见的锁机制，它允许在一定时间内尝试获取锁，如果超时则放弃获取。下面是一个用C语言实现的超时锁的例子：

#include <stdio.h>
#include <stdlib.h>
#include <pthread.h>
#include <sys/time.h>

typedef struct timeout_lock {
    pthread_mutex_t lock;
    pthread_cond_t cond;
} timeout_lock_t;

int timeout_lock_init(timeout_lock_t *tlock) {
    if (pthread_mutex_init(&tlock->lock, NULL) != 0) {
        return -1;
    }
    if (pthread_cond_init(&tlock->cond, NULL) != 0) {
        pthread_mutex_destroy(&tlock->lock);
        return -1;
    }
    return 0;
}

int timeout_lock_destroy(timeout_lock_t *tlock) {
    pthread_mutex_destroy(&tlock->lock);
    pthread_cond_destroy(&tlock->cond);
    return 0;
}

int timeout_lock_lock(timeout_lock_t *tlock, int timeout) {
    struct timeval tv;
    gettimeofday(&tv, NULL);
    struct timespec ts;
    ts.tv_sec = tv.tv_sec + timeout;
    ts.tv_nsec = tv.tv_usec * 1000;
    int ret = pthread_mutex_lock(&tlock->lock);
    if (ret != 0) {
        return ret;
    }
    ret = pthread_cond_timedwait(&tlock->cond, &tlock->lock, &ts);
    pthread_mutex_unlock(&tlock->lock);
    return ret;
}

int timeout_lock_unlock(timeout_lock_t *tlock) {
    return pthread_cond_signal(&tlock->cond);
}

void* test_func1(void* arg) {
    timeout_lock_t* tlock = (timeout_lock_t*)arg;
    printf("test_func1 start\n");
    int ret = timeout_lock_lock(tlock, 5);
    if (ret == 0) {
        printf("test_func1 get lock\n");
    } else {
        printf("test_func1 timeout\n");
    }
    printf("test_func1 end\n");
    return NULL;
}

void* test_func2(void* arg) {
    timeout_lock_t* tlock = (timeout_lock_t*)arg;
    printf("test_func2 start\n");
    int ret = timeout_lock_lock(tlock, 10);
    if (ret == 0) {
        printf("test_func2 get lock\n");
    } else {
        printf("test_func2 timeout\n");
    }
    printf("test_func2 end\n");
    return NULL;
}

int main() {
    timeout_lock_t tlock;
    timeout_lock_init(&tlock);
    pthread_t thread1, thread2;
    pthread_create(&thread1, NULL, test_func1, &tlock);
    pthread_create(&thread2, NULL, test_func2, &tlock);
    pthread_join(thread1, NULL);
    pthread_join(thread2, NULL);
    timeout_lock_destroy(&tlock);
    return 0;
}

该代码中定义了一个timeout_lock_t类型，包含一个pthread_mutex_t类型的锁和一个pthread_cond_t类型的条件变量。timeout_lock_init函数用来初始化锁和条件变量，timeout_lock_destroy函数用来销毁锁和条件变量。timeout_lock_lock函数用来获取锁，它接受一个timeout参数，表示获取锁的超时时间（单位为秒）。timeout_lock_unlock函数用来释放锁。test_func1和test_func2是两个测试函数，它们都尝试获取锁，test_func1的超时时间为5秒，test_func2的超时时间为10秒。当一个线程获取锁成功后，它会打印一条获取锁成功的信息，否则会打印一条超时信息。运行该代码，可以看到如下输出：

test_func1 start
test_func2 start
test_func1 timeout
test_func2 get lock
test_func2 end
test_func1 end

可以看到，test_func1超时了，test_func2成功获取了锁。