python - 事件线程数

Question

Python 版本:'2.7.3(默认，2013 年 4 月 10 日，06:20:15)\n[GCC 4.6.3]'

我有这个:

#!/usr/bin/env python
import time, threading, os
def f1(arg1):
    for i in xrange(arg1):
        time.sleep(1)
        print "i is: ", i
        print threading.active_count()
        print threading.enumerate()

if __name__ == '__main__':

    t = threading.Thread(name="MyThread1", target=f1, args=(5,))
    t.start()

我的问题是，为什么事件线程数报告为 2，为什么 enumerate 生成的列表也包含主线程。

我在想主线程在生成“MyThread1”后终止。

$./threadeg.py

i is:  0
2
[<_MainThread(MainThread, stopped 139858183157504)>, <Thread(MyThread1, started 139858153768704)>]

i is:  1
2
[<_MainThread(MainThread, stopped 139858183157504)>, <Thread(MyThread1, started 139858153768704)>]

i is:  2
2
[<_MainThread(MainThread, stopped 139858183157504)>, <Thread(MyThread1, started 139858153768704)>]

i is:  3
2
[<_MainThread(MainThread, stopped 139858183157504)>, <Thread(MyThread1, started 139858153768704)>]

i is:  4
2
[<_MainThread(MainThread, stopped 139858183157504)>, <Thread(MyThread1, started 139858153768704)>]

Answer 1

threading.activeCount() which returns the number of threads active (that were started with that module). [Source]

由于线程模块是构建在线程模块之上的纯 Python 模块，因此查看源代码非常容易。

这是active_count的源代码

def activeCount():
    """Return the number of Thread objects currently alive.

    The returned count is equal to the length of the list returned by
    enumerate().

    """
    with _active_limbo_lock:
        return len(_active) + len(_limbo)

经过进一步调查，应该注意到有一个 _MainThread 实例存储在 _active 中(_active 和 _limbo 都是将线程名称映射到它们的实例的字典)。并在调用 _exitfunc 时从 _active 中删除。

这是 _MainThread 的源代码，

class _MainThread(Thread):

    def __init__(self):
        Thread.__init__(self, name="MainThread")
        self._Thread__started.set()
        self._set_ident()
        with _active_limbo_lock:
            _active[_get_ident()] = self

    def _set_daemon(self):
        return False

    def _exitfunc(self):
        self._Thread__stop()
        t = _pickSomeNonDaemonThread()
        if t:
            if __debug__:
                self._note("%s: waiting for other threads", self)
        while t:
            t.join()
            t = _pickSomeNonDaemonThread()
        if __debug__:
            self._note("%s: exiting", self)
        self._Thread__delete()

一旦 _exitfunc 被调用，_MainThread 等待所有非守护线程加入，然后调用 Thread._delete，在本例中为 mangled到 __Thread_delete，后者又从 _active 字典中删除 _MainThread。

_exitfunc 被分配给第 1201 行的 _shutdown。

_shutdown = _MainThread()._exitfunc

_shutdown 从 pythonrun.c 调用，然后由 Py_Finalize 调用。 Py_Finalize 由 Py_Exit 调用，退出主进程(此时只剩下守护进程)。

Py_Exit's documentation 。

Exit the current process. This calls Py_Finalize() and then calls the standard C library function exit(status).

这是一个让您获得预期行为的示例。

import threading, time

def f():
    time.sleep(1) #wait for the interpreter to "shutdown"
    print threading.enumerate()

if __name__ == '__main__':

    t = threading.Thread(target=f)
    t.daemon = True
    t.start()

    threading._shutdown() #simulate an interpreter shutdown

另一个很棒的 answer 描述了线程是如何关闭的。