linux - cond problem in pthread
I encountered a problem when learning pthread. I am not sure about it. I will post the code first
#include <pthread.h>
#include <stdio.h>#include <unistd.h>
pthread_cond_t cond;
pthread_mutex_t mutex;
void *Test(void *arg) {
pthread_mutex_lock(&mutex);
while (1) {
pthread_cond_wait(&cond, &mutex);
printf("Got notified\n");
break;
}
pthread_mutex_unlock(&mutex);
return NULL;
}
int main() {
pthread_cond_init(&cond, NULL);
pthread_mutex_init(&mutex, NULL);
pthread_t t;
pthread_create(&t, NULL, Test, NULL);
sleep(1);
pthread_mutex_lock(&mutex);
pthread_cond_signal(&cond);
pthread_mutex_unlock(&mutex);
pthread_join(t, NULL);
printf("Exit\n");
}
If sleep(1) is commented out, it will fall into infinite waiting. If you add it (I personally think it is to ensure that another thread is already waiting to wake up before the main thread's signal), you can output two log sentences normally and exit. The reason for this phenomenon can be understood as because a thread falls into sleep because of cond_wait. Can it be woken up only by signaling cond after it sleeps? I searched online and couldn't find any article that said it specifically. Hope you can give me some advice. Or help me confirm, for a cond, assuming that thread A first calls cond_signal, and then B calls cond_wait, can B be awakened?
