c++ - 线程内的死锁

Question

所以我的系统中出现了死锁，而且我终究无法弄清楚死锁在哪里。

基本上在我的系统中，我有一个包含 12 个元素的数组和对应于每个元素的 12 个锁。然后我有 2 个线程创建一个对数组执行计算的函数。但是每个线程一次在数组中执行两个元素更改。

如果每个线程只查看一个元素，则不会出现死锁，但如果每个线程查看两个元素，则很少会出现死锁。

这是我的代码:

Thread() {

           - some other code that doesnt effect the threads -

           // randomly pick a lane between 0 - 15
           randLane1 = rand() % 16;
           randLane2 = rand() % 16;

           pthread_mutex_lock(&mutexFineLock[randLane1]);
           pthread_mutex_lock(&mutexFineLock[randLane2]);

           // if Rouge picked a lane that has already been fired at, look for a free lane
           while(Gallery->Get(randLane1) != white) {
              pthread_mutex_unlock(&mutexFineLock[randLane1]);
              randLane1 = rand() % 16;
              pthread_mutex_lock(&mutexFineLock[randLane1]);
           }
           while(Gallery->Get(randLane2) != white || randLane2 == randLane1) {
              pthread_mutex_unlock(&mutexFineLock[randLane2]);
              randLane2 = rand() % 16;
              pthread_mutex_lock(&mutexFineLock[randLane2]);
           }

           // set the lane's colour
           Gallery->Set(randLane1, PlayerColor);
           Gallery->Set(randLane2, PlayerColor);
           // set the thread to wait X amount of time to simulate a shot        
           usleep(1000000/rate);

           // upon lock for other threads
           pthread_mutex_unlock(&mutexFineLock[randLane1]);
           pthread_mutex_unlock(&mutexFineLock[randLane2]);


}

如果有人能够查明死锁发生的位置，那将是非常有帮助的。如果您需要我进一步说明系统，请询问。

Answer 1

在这部分代码中:

while(Gallery->Get(randLane2) != white || randLane2 == randLane1) {
    pthread_mutex_unlock(&mutexFineLock[randLane2]);
    randLane2 = rand() % 16;
    pthread_mutex_lock(&mutexFineLock[randLane2]);
}

当 randLand2 == randlane1;

pthread_mutex_lock(&mutexFineLock[randLane2]);

永远不会成功，因为互斥体已经被锁定。为了避免这个问题；你可能会考虑做这样的事情:

int lockAcquired = 0;
while(!lockAcquired && Gallery->Get(randLane2) != white || randLane2 == randLane1) {
    pthread_mutex_unlock(&mutexFineLock[randLane2]);
    randLane2 = rand() % 16;
    if (pthread_mutex_trylock(&mutexFineLock[randLane2]))
        lockAcquired = 1;
}