python中start和run方法的区别
作者:小槿12358
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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