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python start和run方法

小槿12358 人气:0

结论:启动线程,如果对target进行赋值,并且没有重写run方法,则线程start的时候会直接调用target中对应的方法

具体代码如下:
1、初始化一个线程

threading.Thread.__init__(self,target=thread_run())

def __init__(self, group=None, target=None, name=None,
                 args=(), kwargs=None, *, daemon=None):
        assert group is None, "group argument must be None for now"
        if kwargs is None:
            kwargs = {}
        self._target = target
        self._name = str(name or _newname())
        self._args = args
        self._kwargs = kwargs

2、调用start启动线程
最终调用_start_new_thread方法,self._bootstrap作为传参

thread1.start()
    def start(self):
        if not self._initialized:
            raise RuntimeError("thread.__init__() not called")
        if self._started.is_set():
            raise RuntimeError("threads can only be started once")
        with _active_limbo_lock:
            _limbo[self] = self
        try:
            _start_new_thread(self._bootstrap, ())
        except Exception:
            with _active_limbo_lock:
                del _limbo[self]
            raise
        self._started.wait()

3、_start_new_thread等同于启动一个新线程,并在新线程中调用回调函数

_start_new_thread = _thread.start_new_thread
def start_new_thread(function: Callable[..., Any], args: tuple[Any, ...], kwargs: dict[str, Any] = ...) -> int: ...

4、执行的回调函数就是上文传入的self._bootstrap, _bootstrap方法直接调用_bootstrap_inner(),而bootstrap_inner则调用run方法

def _bootstrap_inner(self):
    try:
        self._set_ident()
        self._set_tstate_lock()
        if _HAVE_THREAD_NATIVE_ID:
            self._set_native_id()
        self._started.set()
        with _active_limbo_lock:
            _active[self._ident] = self
            del _limbo[self]

        if _trace_hook:
            _sys.settrace(_trace_hook)
        if _profile_hook:
            _sys.setprofile(_profile_hook)
        try:
            self.run()

5、最终调用run方法

 def run(self):
        try:
            if self._target:
                self._target(*self._args, **self._kwargs)
        finally:
            # Avoid a refcycle if the thread is running a function with
            # an argument that has a member that points to the thread.
            del self._target, self._args, self._kwargs

结论:
如果run方法被重写,则直接调用重写的run方法
如果run方法没有被重写,并且target被定义,则会直接调用线程创建时候的target方法,否则什么也不做

此处遇到一问题:
指定target参数,在执行过程中,打印的进程名mainthread(主进程),而不是之前所赋的进程名
threading.Thread.init(self,target=thread_run())
分析后发现赋予target的是执行的函数体,因此会先执行thread_run函数,执行结束后,将thread_run的返回值赋给了target,因为thread_run没有返回值,因此target的值是None,如果此时没有重写run函数,那么线程什么都不会做。 thread_run的执行是在主线程,而不是我们所认为的在子线程中执行thread_run

def thread_run():
    print ("overwrite: 开始线程:" + threading.current_thread().name)
    time.sleep(2)
    print ("overwrite: 退出线程:" + threading.current_thread().name)

class myThread (threading.Thread):
    def __init__(self, threadID, name, delay):
        threading.Thread.__init__(self,target=thread_run())
        self.threadID = threadID
        self.name = name
        self.delay = delay
        thread1.start()

thread1.join()
print ("退出主线程")

运行结果:

overwrite: 开始线程:MainThread
overwrite: 退出线程:MainThread
退出主线程

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