如何查询pthread以查看它是否仍在运行？ [英] How do you query a pthread to see if it is still running?
问题描述
在我的析构函数中，我想要清除一个线程。
我的目标是等待一个线程完成执行，然后销毁线程。
我发现有关查询pthread的状态的唯一方法是 pthread_attr_setdetachstate ，但这只会告诉您您的主题是否为：
- PTHREAD_CREATE_DETACHED
- PTHREAD_CREATE_JOINABLE
这些都与线程是否仍在运行无关。
如何查询pthread以查看它是否仍在运行？
这里似乎有两个问题：
如何等到我的线程完成？
答案：这是由pthreads直接支持的 - 使你的线程被停止的JOINABLE（当它第一次启动），并使用pthread_join（）阻塞当前线程，直到线程待-stopped不再运行。
如何判断我的线程是否仍在运行？
答案：你可以添加一个thread_complete标志来执行：
场景：线程A想知道线程B是否
当线程B被创建时，它被赋予一个指向thread_complete标志地址的指针。在创建线程之前，thread_complete标志应初始化为NOT_COMPLETED。线程B的入口点函数应该立即调用pthread_cleanup_push（）推送一个清理处理程序，将thread_complete标志设置为COMPLETED。
有关清理处理程序的详细信息， pthread清理处理程序
您将需要包括相应的pthread_cleanup_pop（1）调用，以确保清除处理程序被调用，无论什么（即如果线程退出正常或由于取消等）。
然后，线程A可以简单地检查thread_complete标志，看看线程B是否已经退出。
注意：你的thread_complete 标志应该被声明为volatile，并且应该是一个原子类型 - GNU编译器为此目的提供sig_atomic_t。这允许两个线程一致地访问相同的数据，而不需要同步结构（互斥体/信号量）。
In my destructor I want to destroy a thread cleanly.
My goal is to wait for a thread to finish executing and THEN destroy the thread.
The only thing I found about querying the state of a pthread is pthread_attr_setdetachstate but this only tells you if your thread is:
- PTHREAD_CREATE_DETACHED
- PTHREAD_CREATE_JOINABLE
Both of those have nothing to do with whether the thread is still running or not.
How do you query a pthread to see if it is still running?
It sounds like you have two questions here:
How can I wait until my thread completes?
Answer: This is directly supported by pthreads -- make your thread-to-be-stopped JOINABLE (when it is first started), and use pthread_join() to block your current thread until the thread-to-be-stopped is no longer running.
How can I tell if my thread is still running?
Answer: You can add a "thread_complete" flag to do the trick:
Scenario: Thread A wants to know if Thread B is still alive.
When Thread B is created, it is given a pointer to the "thread_complete" flag address. The "thread_complete" flag should be initialized to NOT_COMPLETED before the thread is created. Thread B's entry point function should immediately call pthread_cleanup_push() to push a "cleanup handler" which sets the "thread_complete" flag to COMPLETED.
See details about cleanup handlers here: pthread cleanup handlers
You'll want to include a corresponding pthread_cleanup_pop(1) call to ensure that the cleanup handler gets called no matter what (i.e. if the thread exits normally OR due to cancellation, etc.).
Then, Thread A can simply check the "thread_complete" flag to see if Thread B has exited yet.
NOTE: Your "thread_complete" flag should be declared "volatile" and should be an atomic type -- the GNU compilers provide the sig_atomic_t for this purpose. This allows the two threads consistent access the same data without the need for synchronization constructs (mutexes/semaphores).
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