/* Reset the cancellation flag to avoid looping if the cleanup handlers contain cancellation points */ // 设置成0，避免其他函数里判断是cancel状态，然后再调pthread_exit函数 self->p_canceled = 0; /* Call cleanup functions and destroy the thread-specific data */ // 执行clean节点的函数 __pthread_perform_cleanup(); // 遍历pthread_keys数组，销毁线程中的specifics数据 __pthread_destroy_specifics(); /* Store return value */ // 加锁 acquire(&self->p_spinlock); // 退出值,可以在join中返回给其他线程 self->p_retval = retval; /* Say that we've terminated */ // 已终止 self->p_terminated = 1; /* See if someone is joining on us */ // 判断有没有其他线程在等待该线程退出 joining = self->p_joining; release(&self->p_spinlock); /* Restart joining thread if any */ // 唤醒他 if (joining != NULL) restart(joining); /* If this is the initial thread, block until all threads have terminated. If another thread calls exit, we'll be terminated from our signal handler. */ // 如果是主线程退出，通知manage线程，如果是一般线程则直接执行exit退出 if (self == __pthread_main_thread && __pthread_manager_request >= 0) { request.req_thread = self; request.req_kind = REQ_MAIN_THREAD_EXIT; // 写入管道 __libc_write(__pthread_manager_request, (char *)&request, sizeof(request)); // 挂起等待唤醒，全部子线程都退出后了才唤醒主线程，然后主线程也退出,见manager.c的__pthread_manager函数 suspend(self); } /* Exit the process (but don't flush stdio streams, and don't run atexit functions). */ // 线程退出，见操作系统实现 _exit(0); }
2 pthread_join
// 调用该函数的线程会等待th线程结束 int pthread_join(pthread_t th, void ** thread_return) { volatile pthread_t self = thread_self(); struct pthread_request request; // 不能等待自己结束，否则会死锁，即自己无法结束 if (th == self) return EDEADLK; acquire(&th->p_spinlock); /* If detached or already joined, error */ // th线程已经是detach状态，即不是joinable的，或者已经被jion过了 if (th->p_detached || th->p_joining != NULL) { release(&th->p_spinlock); return EINVAL; } /* If not terminated yet, suspend ourselves. */ // join的线程还在运行，则需要等待 if (! th->p_terminated) { // 记录谁在join th th->p_joining = self; release(&th->p_spinlock); // 挂起等待唤醒，th退出的时候才会唤醒self线程，见pthread_exit的restart suspend_with_cancellation(self); acquire(&th->p_spinlock); /* This is a cancellation point */ // 取消点 if (self->p_canceled && self->p_cancelstate == PTHREAD_CANCEL_ENABLE) { th->p_joining = NULL; release(&th->p_spinlock); pthread_exit(PTHREAD_CANCELED); } } /* Get return value */ // 线程已经结束，设置线程的返回值 if (thread_return != NULL) *thread_return = th->p_retval; release(&th->p_spinlock); /* Send notification to thread manager */ // 管道的写端，join的线程已经退出，通知manage线程回收退出线程的资源，见REQ_FREE的处理 if (__pthread_manager_request >= 0) { // 发送th线程已经结束的通知给manager线程，self是发送者 request.req_thread = self; request.req_kind = REQ_FREE; request.req_args.free.thread = th; // 写入管道 __libc_write(__pthread_manager_request, (char *) &request, sizeof(request)); } return 0; }
3 pthread_detach
int pthread_detach(pthread_t th) { int terminated; struct pthread_request request;
acquire(&th->p_spinlock); /* If already detached, error */ // detach过了 if (th->p_detached) { release(&th->p_spinlock); return EINVAL; } /* If already joining, don't do anything. */ // 有线程join了该线程，不能detach if (th->p_joining != NULL) { release(&th->p_spinlock); return 0; } /* Mark as detached */ // 标记已经detach th->p_detached = 1; terminated = th->p_terminated; release(&th->p_spinlock); /* If already terminated, notify thread manager to reclaim resources */ // 线程已经退出了，detach的时候，通知manager,__pthread_manager_request是管道写端 if (terminated && __pthread_manager_request >= 0) { request.req_thread = thread_self(); request.req_kind = REQ_FREE; request.req_args.free.thread = th; __libc_write(__pthread_manager_request, (char *) &request, sizeof(request)); } return 0; }
