pthread_exit

pthread_exit：

• By having main() explicitly call pthread_exit() as the last thing it does, main() will block and be kept alive to support the threads it created until they are done.

就是说，main函数中调用pthread_exit的时候，进程不会退出，所以main创建的线程就不会退出，但是main的局部变量存储的堆栈应该已经释放了。见如下代码：

/*****************************************************************************
* FILE: hello_arg3.c
* DESCRIPTION:
*   This "hello world" Pthreads program demonstrates an unsafe (incorrect)
*   way to pass thread arguments at thread creation.  In this case, the
*   argument variable is changed by the main thread as it creates new threads.
* AUTHOR: Blaise Barney
* LAST REVISED: 07/16/14
******************************************************************************/
#include <pthread.h>
#include <stdio.h>
#include <stdlib.h>
#define NUM_THREADS     8

void *PrintHello(void *threadid)
{
   long taskid;
   sleep(1);
   taskid = *(long *)threadid;
   printf("Hello from thread %ld\n", taskid);
   pthread_exit(NULL);
}

int main(int argc, char *argv[])
{
pthread_t threads[NUM_THREADS];
int rc;
long t;

for(t=0;t<NUM_THREADS;t++) {
  printf("Creating thread %ld\n", t);
  rc = pthread_create(&threads[t], NULL, PrintHello, (void *) &t);
  if (rc) {
    printf("ERROR; return code from pthread_create() is %d\n", rc);
    exit(-1);
    }
   }

pthread_exit(NULL);
}

输出：

Creating thread 0
Creating thread 1
Creating thread 2
Creating thread 3
Creating thread 4
Creating thread 5
Creating thread 6
Creating thread 7
Hello from thread 140737488348392
Hello from thread 140737488348392
Hello from thread 140737488348392
Hello from thread 140737488348392
Hello from thread 140737488348392
Hello from thread 140737488348392
Hello from thread 140737488348392
Hello from thread 140737488348392

当我们在pthread_exit(NULL)的前面加sleep(10)的时候输出是：

Creating thread 0
Creating thread 1
Creating thread 2
Creating thread 3
Creating thread 4
Creating thread 5
Creating thread 6
Creating thread 7
Hello from thread 8
Hello from thread 8
Hello from thread 8
Hello from thread 8
Hello from thread 8
Hello from thread 8
Hello from thread 8
Hello from thread 8

 另外需注意：void *类型表示没有指定类型的指针

参考资料：https://computing.llnl.gov/tutorials/pthreads/