pthread_exit函数

void pthread_exit(void *retval); 参数：retval表示线程退出状态，通常传NULL。

作用：将单个线程退出。

注意几点：

return的作用是返回到函数的调用点，如果是main函数中的return，则代表该进程结束，并释放进程地址空间，所有线程都终止。对于其它函数的return，则直接返回到函数的调用点。exit和_exit函数会直接终止整个进程，导致所有线程结束。pthread_exit函数则会导致调用该函数的线程结束。所以，多线程环境中，应尽量少用，或者不使用exit函数，取而代之使用pthread_exit函数，将单个线程退出。任何线程里exit导致进程退出，其他线程也结束，主控线程退出时不能return或exit。
另注意，pthread_exit或者return返回的指针（线程执行的函数用return或者pthread_exit结束线程时）所指向的内存单元必须是全局的或者是用malloc分配的，不能在线程函数的栈上分配，因为当其它线程得到这个返回指针时线程函数已经退出了，此时退出的这个线程函数所占据的栈空间可能又会被重新分配出去，因此其他线程再次使用这个返回的地址没有意义。

//代码示例

#include <stdio.h>
#include <pthread.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>void *tfn(void *arg)
{int s = (int)arg;printf("The %dth thread: the process id is %d and thread id is %lu.\n",s+1,getpid( ),pthread_self( ));return NULL;
}int main(int argc,char *argv[ ])
{pthread_t tid;int ret, i, n=5;if(argc == 2)n = atoi(argv[1]);for( i=0;i<n;i++ ){ret = pthread_create(&tid, NULL, tfn,(void *)i);if( ret != 0 ){fprintf(stderr,"pthread_create error: %s\n",strerror(ret));exit(1);}}printf("In main: the process id is %u and thread id is %lu.\n",getpid( ),pthread_self( ));pthread_exit( NULL );
}

[root@localhost 01_pthread_test]# ./pthrd_crt 10

The 1th thread: the process id is 9035 and thread id is 4149640000.

The 4th thread: the process id is 9035 and thread id is 4124461888.

The 7th thread: the process id is 9035 and thread id is 4099283776.

The 9th thread: the process id is 9035 and thread id is 4082498368.

In main: the process id is 9035 and thread id is 4151699712.

The 6th thread: the process id is 9035 and thread id is 4107676480.

The 8th thread: the process id is 9035 and thread id is 4090891072.

The 5th thread: the process id is 9035 and thread id is 4116069184.

The 10th thread: the process id is 9035 and thread id is 4074105664.

The 2th thread: the process id is 9035 and thread id is 4141247296.

The 3th thread: the process id is 9035 and thread id is 4132854592.