Linux多线程编程 - sleep 和 pthread_cond_timedwait

#include <stdio.h>

#include <stdlib.h>

int flag = 1;

void * thr_fn(void * arg)

{  

while (flag)

{    

printf("******\n");    

sleep(10);  

}  

printf("sleep test thread exit\n");

}  

int main()

{  

pthread_t thread;  

if (0 != pthread_create(&thread, NULL, thr_fn, NULL))

{    

printf("error when create pthread,%d\n", errno);    

return 1;  

}    

char c ;  

while ((c = getchar()) != 'q');    

printf("Now terminate the thread!\n");  

flag = 0;  

printf("Wait for thread to exit\n");  

pthread_join(thread, NULL);  

printf("Bye\n");   return 0;

}

输入q后，需要等线程从sleep中醒来（由挂起状态变为运行状态），即最坏情况要等10s，线程才会被join。采用sleep的缺点：不能及时唤醒线程。

 

采用pthread_cond_timedwait函数，条件到了，线程即会被join，可及时唤醒线程。实现的如下：

#include <stdio.h>

#include <sys/time.h>

#include <unistd.h>

#include <pthread.h>

#include <errno.h>  

static pthread_t thread;

static pthread_cond_t cond;

static pthread_mutex_t mutex;

static int flag = 1;  

void * thr_fn(void * arg)

{  

struct timeval now;  

struct timespec outtime;  

pthread_mutex_lock(&mutex);  

while (flag)

{    

printf("*****\n");    

gettimeofday(&now, NULL);    

outtime.tv_sec = now.tv_sec + 5;    

outtime.tv_nsec = now.tv_usec * 1000;    

pthread_cond_timedwait(&cond, &mutex, &outtime);  

}  

pthread_mutex_unlock(&mutex);  

printf("cond thread exit\n");

}  

int main(void)

{  

pthread_mutex_init(&mutex, NULL);  

pthread_cond_init(&cond, NULL);  

if (0 != pthread_create(&thread, NULL, thr_fn, NULL))

{    

printf("error when create pthread,%d\n", errno);    

return 1;  

}  

char c ;  

while ((c = getchar()) != 'q');  

printf("Now terminate the thread!\n");

pthread_mutex_lock(&mutex);  

flag = 0;  

pthread_cond_signal(&cond);  

pthread_mutex_unlock(&mutex);  

printf("Wait for thread to exit\n");  

pthread_join(thread, NULL);  

printf("Bye\n");  

return 0;

}

pthread_cond_timedwait()函数阻塞住调用该函数的线程，等待由cond指定的条件被触发（pthread_cond_broadcast() or pthread_cond_signal()）。

　　当pthread_cond_timedwait()被调用时，调用线程必须已经锁住了mutex。函数pthread_cond_timedwait()会对mutex进行【解锁和执行对条件的等待】（原子操作）。