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hao爱做网站,梵美传媒网站是谁做的,wordpress 3.8 侧边栏仪表盘,网络营销是什么证死锁检测组件-设想现在有三个临界资源和三把锁绑定了，三把锁又分别被三个线程占用。（不用关注临界资源，因为锁和临界资源是绑定的） 但现在出现这种情况：线程1去申请获取锁2，线程2申请获取锁3，…

死锁检测组件-设想

现在有三个临界资源和三把锁绑定了，三把锁又分别被三个线程占用。（不用关注临界资源，因为锁和临界资源是绑定的）

但现在出现这种情况：线程1去申请获取锁2，线程2申请获取锁3，线程3申请获取锁1，这样就会造成死锁：

死锁问题，可转换为有向图的环路检测

死锁的构建

有四个线程，4把锁，以下代码一定会产生死锁


pthread_mutex_t mtx1 = PTHREAD_MUTEX_INITIALIZER;
pthread_mutex_t mtx2 = PTHREAD_MUTEX_INITIALIZER;
pthread_mutex_t mtx3 = PTHREAD_MUTEX_INITIALIZER;
pthread_mutex_t mtx4 = PTHREAD_MUTEX_INITIALIZER;void *thread_routine_a(void *arg) {printf("thread_routine a \n");pthread_mutex_lock(&mtx1);sleep(1);	pthread_mutex_lock(&mtx2);pthread_mutex_unlock(&mtx2);pthread_mutex_unlock(&mtx1);printf("thread_routine a exit\n");}void *thread_routine_b(void *arg) {printf("thread_routine b \n");pthread_mutex_lock(&mtx2);sleep(1);pthread_mutex_lock(&mtx3);pthread_mutex_unlock(&mtx3);pthread_mutex_unlock(&mtx2);printf("thread_routine b exit \n");
// -----pthread_mutex_lock(&mtx1);
}void *thread_routine_c(void *arg) {printf("thread_routine c \n");pthread_mutex_lock(&mtx3);sleep(1);pthread_mutex_lock(&mtx4);pthread_mutex_unlock(&mtx4);pthread_mutex_unlock(&mtx3);printf("thread_routine c exit \n");
}void *thread_routine_d(void *arg) {printf("thread_routine d \n");pthread_mutex_lock(&mtx4);sleep(1);pthread_mutex_lock(&mtx1);pthread_mutex_unlock(&mtx1);pthread_mutex_unlock(&mtx4);printf("thread_routine d exit \n");
}int main() {
#if 1init_hook();pthread_t tid1, tid2, tid3, tid4;pthread_create(&tid1, NULL, thread_routine_a, NULL);pthread_create(&tid2, NULL, thread_routine_b, NULL);pthread_create(&tid3, NULL, thread_routine_c, NULL);pthread_create(&tid4, NULL, thread_routine_d, NULL);pthread_join(tid1, NULL);pthread_join(tid2, NULL);pthread_join(tid3, NULL);pthread_join(tid4, NULL);
}

这里产生了：线程a => 线程b => 线程c => 线程d =》线程a的这样一个环路

但是我们不知道哪把锁被哪个线程占用了，没法构建有向图，也就无法得知是否产生了这样一个环路

这时，可以用hook，调自己写的 pthread_mutex_lock，将线程和锁的映射关系保存起来

pthread的hook

有点像装饰器模式

// 函数指针
typedef int (*pthread_mutex_lock_t)(pthread_mutex_t *mutex);
pthread_mutex_lock_t pthread_mutex_lock_f;typedef int (*pthread_mutex_unlock_t)(pthread_mutex_t *mutex);
pthread_mutex_unlock_t pthread_mutex_unlock_f;static int init_hook() {//  RTLD_NEXT可以理解为代码段，在这里面找pthread_mutex_lock函数名，把地址返回// 所以pthread_mutex_lock_f就是静态或动态库里的pthread_mutex_lock锁函数  pthread_mutex_lock_f = dlsym(RTLD_NEXT, "pthread_mutex_lock"); pthread_mutex_unlock_f = dlsym(RTLD_NEXT, "pthread_mutex_unlock");
}int pthread_mutex_lock(pthread_mutex_t *mutex) {printf("pthread_mutex_lock selfid %ld, mutex: %p\n", pthread_self(), mutex);beforelock(pthread_self(), mutex);pthread_mutex_lock_f(mutex);    // 用钩子的好处，给系统函数命一个别名afterlock(pthread_self(), mutex);}int pthread_mutex_unlock(pthread_mutex_t *mutex) {printf("pthread_mutex_unlock\n");pthread_mutex_unlock_f(mutex);afterunlock(pthread_self(), mutex);}

这样，在加锁的时候，就能知道锁id(mutex)和线程id的对应关系