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）。