多线程pthread_detach的奇怪问题，求详细解答

rowdzfda

在unix高级编程2中，关于pthread_detach有以下描述：
a thread's termination status is retained until pthread_join is called for that thread. A thread's underlying storage can be reclaimed immediately on termination if that thread has been detached. When a thread is detached, the pthread_join function can't be used to wait for its termination status. A call to pthread_join for a detached thread will fail, returning EINVAL. We can detach a thread by calling pthread_detach.

因此我想先对一个子线程调用pthread_detach，然后再对其pthread_join，测试一下是否会返回EINVAL值。但结果有点迷惑不解。

#include <pthread.h> #include <iostream> #include <errno.h> using namespace std; pthread_t ntid; void printids(const char *s) { &nbsp;&nbsp;&nbsp;&nbsp;pid_t      pid; &nbsp;&nbsp;&nbsp;&nbsp;pthread_t  tid; &nbsp;&nbsp;&nbsp;&nbsp;pid = getpid(); &nbsp;&nbsp;&nbsp;&nbsp;tid = pthread_self(); &nbsp;&nbsp;&nbsp;&nbsp;printf("%s pid %u tid %u (0x%x)\n", s, (unsigned int)pid, &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(unsigned int)tid, (unsigned int)tid); } void * thr_fn(void *arg) { &nbsp;&nbsp;&nbsp;&nbsp;printids("new thread: "); &nbsp;&nbsp;&nbsp;&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;int err = pthread_detach(pthread_self()); &nbsp;&nbsp;&nbsp;&nbsp;if (err != 0) &nbsp;&nbsp;&nbsp;&nbsp;{ &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;printf("can't detach thread: err = %d, %s\n", err, strerror(err)); &nbsp;&nbsp;&nbsp;&nbsp;} &nbsp;&nbsp;&nbsp;&nbsp;return((void *)0); } int main(void) { &nbsp;&nbsp;&nbsp;&nbsp;int     err; &nbsp;&nbsp;&nbsp;&nbsp;err = pthread_create(&ntid, NULL, thr_fn, NULL); &nbsp;&nbsp;&nbsp;&nbsp;if (err != 0) &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;printf("can't create thread: %s\n", strerror(err)); &nbsp;&nbsp;&nbsp;&nbsp;printids("main thread:"); &nbsp;&nbsp;&nbsp;&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;sleep(1);    //这个sleep非常重要，是否存在会产生不同的结果 &nbsp;&nbsp;&nbsp;&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;err = pthread_join(ntid, NULL); &nbsp;&nbsp;&nbsp;&nbsp;if (err != 0) &nbsp;&nbsp;&nbsp;&nbsp;{ &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;printf("can't join thread: err = %d, %s\n", err, strerror(err)); &nbsp;&nbsp;&nbsp;&nbsp;} &nbsp;&nbsp;&nbsp;&nbsp;return 0; }

当main函数中的sleep(1)语句存在时，回来的结果正确为：
main thread: pid 573810 tid 1 (0x1)
new thread:  pid 573810 tid 258 (0x102)
can't join thread: err = 22, Invalid argument

但注释该sleep(1)时，程序的结果会是：
main thread: pid 573810 tid 1 (0x1)
new thread:  pid 573810 tid 258 (0x102)
也就是说pthread_join正确处理了，返回了0.

我猜测是否是因为子线程在pthread_detach后，资料还未来得及释放，join函数就开始调用了，才导致该结果？

rain_fish

是的，所以一般的做法是创建的线程发一个信号，创建线程等待这个信号后，再去做别的

peidright

int err = pthread_detach(pthread_self());
在这句后打印个printf("aaa");，前面打印个printf("aaa");试试。
。。。。正在开机，我测试下

peidright

如果不sleep,detach 在join后执行。join后，再detach?...额。。为什么detach不出错？
sleep(0.1)的话，主线程就一直等待子线程退出了。。。比较有意思。

[ 本帖最后由 peidright 于 2009-10-17 13:15 编辑 ]

rowdzfda

恩，不sleep，detach不会报错，仍然能正常detach。对这个结果非常的迷惑，想弄清楚具体原因