NAME

pthread_join - wait for thread termination  等待直到线程终止

SYNOPSIS

#include <pthread.h>

int pthread_join(pthread_t thread, void **value_ptr);

DESCRIPTION

The  pthread_join() function suspends execution of the calling thread until the target  thread terminates, unless the target  thread has already terminated. On return from a successful  pthread_join() call with a non-NULL  value_ptr argument, the value passed to  pthread_exit() by the terminating thread is made available in the location referenced by  value_ptr. When a  pthread_join() returns successfully, the target thread has been terminated. The results of multiple simultaneous calls to  pthread_join() specifying the same target thread are undefined. If the thread calling  pthread_join() is canceled, then the target thread will not be detached.

It is unspecified whether a thread that has exited but remains unjoined counts against _POSIX_THREAD_THREADS_MAX.

RETURN VALUE

If successful, the  pthread_join() function returns zero. Otherwise, an error number is returned to indicate the error.

ERRORS

The  pthread_join() function will fail if:

[EINVAL]

The implementation has detected that the value specified by  thread does not refer to a joinable thread.

[ESRCH]

No thread could be found corresponding to that specified by the given thread ID.

The pthread_join() function may fail if:

[EDEADLK]

A deadlock was detected or the value of  thread specifies the calling thread.

The pthread_join() function will not return an error code of [EINTR].

EXAMPLES

None.

APPLICATION USAGE

None.

FUTURE DIRECTIONS

None.

int pthread_join(pthread_t thread, void **value_ptr);

thread：等待退出线程的线程号。

value_ptr：退出线程的返回值。

范例：

//pthread_join.c
// 子线程阻塞，等待信号，然后输出字符串
// 主线程从键盘录入字符，给子线程发信号。

 

#include <stdio.h>

#include <unistd.h>

#include <signal.h>

#include <pthread.h>

#include <time.h>

 

pthread_t tid;
sigset_t set;

 

void myfunc()
{
 printf("hello\n");
}

 

static void* mythread(void *p)
{
 int signum;
 while(1){
  sigwait(&set,&signum);
  if(SIGUSR1 == signum)
   myfunc();
  if(SIGUSR2 == signum)
  {
   printf("I will sleep 2 second and exit\n");
   sleep(2);
   break;
  }
 }

}

 

int main()
{
 char tmp;
 void* status;
 sigemptyset(&set);
 sigaddset(&set,SIGUSR1);
 sigaddset(&set,SIGUSR2);
 sigprocmask(SIG_SETMASK,&set,NULL);
  
 pthread_create(&tid,NULL,mythread,NULL);

 while(1)
 {
  printf(":");
  scanf("%c",&tmp);
  if('a' == tmp)
  {
   pthread_kill(tid,SIGUSR1);  //发送SIGUSR1，打印字符串。
  }
  else if('q'==tmp)
  {
   pthread_kill(tid,SIGUSR2);  //发出SIGUSR2信号，让线程退出，如果发送SIGKILL，线程将直接退出。
   pthread_join(tid,&status);  //等待线程tid执行完毕，这里阻塞。
   printf("finish\n");
   break;
  }
  else
   continue;    
 } 
 
 return 0;
}

 

编译  gcc -o pthread_join -lpthread pthread_join.c

运行结果：

// 如果输入a，子线程打印"hello"，主程序继续等待输入；

// 如果输入q，主程序等待子程序结束。子线程打印"I will sleep 2 second and exit"，并延时两秒后结束。主线程随之打印"finish"，程序结束。