等待線程
1。使用pthread_cond_wait前要先加鎖
2。pthread_cond_wait內(nèi)部會(huì)解鎖，然后等待條件變量被其它線程激活
3。pthread_cond_wait被激活后會(huì)再自動(dòng)加鎖

激活線程：
1。加鎖（和等待線程用同一個(gè)鎖）
2。pthread_cond_signal發(fā)送信號(hào)
3。解鎖
激活線程的上面三個(gè)操作在運(yùn)行時(shí)間上都在等待線程的pthread_cond_wait函數(shù)內(nèi)部。

程序示例：

#include <stdio.h>
#include <pthread.h>
#include <unistd.h>

pthread_mutex_t count_lock;
pthread_cond_t count_nonzero;
unsigned count = 0;

void * decrement_count(void *arg) {
pthread_mutex_lock (&count_lock);
printf("decrement_count get count_lock\n");
while(count==0) {
printf("decrement_count count == 0 \n");
printf("decrement_count before cond_wait \n");
pthread_cond_wait( &count_nonzero, &count_lock);
printf("decrement_count after cond_wait \n");
}
count = count -1;
pthread_mutex_unlock (&count_lock);
}

void * increment_count(void *arg){
pthread_mutex_lock(&count_lock);
printf("increment_count get count_lock\n");
if(count==0) {
printf("increment_count before cond_signal\n");
pthread_cond_signal(&count_nonzero);
printf("increment_count after cond_signal\n");
}
count=count+1;
pthread_mutex_unlock(&count_lock);
}

int main(void)
{
pthread_t tid1,tid2;

pthread_mutex_init(&count_lock,NULL);
pthread_cond_init(&count_nonzero,NULL);

pthread_create(&tid1,NULL,decrement_count,NULL);
sleep(2);
pthread_create(&tid2,NULL,increment_count,NULL);

sleep(10);
pthread_exit(0);
}

 

 

2.decrement_count和increment_count在兩個(gè)線程A和B中被調(diào)用。