Python线程join和setDaemon

看一下线程的setDaemon()方法

import time
import threading
import ctypes
import inspectdef sayHello():for i in range(10):print("hello")time.sleep(1)def _async_raise(tid, exctype):"""raises the exception, performs cleanup if needed"""tid = ctypes.c_long(tid)if not inspect.isclass(exctype):exctype = type(exctype)res = ctypes.pythonapi.PyThreadState_SetAsyncExc(tid, ctypes.py_object(exctype))if res == 0:raise ValueError("invalid thread id")elif res != 1:# """if it returns a number greater than one, you're in trouble,# and you should call it again with exc=NULL to revert the effect"""ctypes.pythonapi.PyThreadState_SetAsyncExc(tid, None)raise SystemError("PyThreadState_SetAsyncExc failed")def stop_thread(thread):_async_raise(thread.ident, SystemExit)if __name__ == '__main__':# sayHello()t = threading.Thread(target=sayHello, args=())t.setDaemon(True) # 主线程结束后停止子线程t.start()for i in range(3):print(t.is_alive())time.sleep(1)

上面的输出是：

hello
True
True
hello
hello
True
hello

我们修改一下代码：

'''
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'''
import time
import threading
import ctypes
import inspectdef sayHello():for i in range(10):print("hello")time.sleep(1)def _async_raise(tid, exctype):"""raises the exception, performs cleanup if needed"""tid = ctypes.c_long(tid)if not inspect.isclass(exctype):exctype = type(exctype)res = ctypes.pythonapi.PyThreadState_SetAsyncExc(tid, ctypes.py_object(exctype))if res == 0:raise ValueError("invalid thread id")elif res != 1:# """if it returns a number greater than one, you're in trouble,# and you should call it again with exc=NULL to revert the effect"""ctypes.pythonapi.PyThreadState_SetAsyncExc(tid, None)raise SystemError("PyThreadState_SetAsyncExc failed")def stop_thread(thread):_async_raise(thread.ident, SystemExit)if __name__ == '__main__':# sayHello()t = threading.Thread(target=sayHello, args=())t.setDaemon(False) # 主线程结束后不停止子线程t.start()for i in range(3):print(t.is_alive())time.sleep(1)

程序的输出是：

hello
True
True
hello
hello
True
hello
hello
hello
hello
hello
hello
hello

可见，setDaemon()方法就是决定在主线程结束后是否结束子线程，如果为True时，会结束子线程，为False时，不会结束子线程。

我们再来看join()方法：

直接看代码

'''
遇到问题没人解答？小编创建了一个Python学习交流QQ群：778463939
寻找有志同道合的小伙伴，互帮互助,群里还有不错的视频学习教程和PDF电子书！
'''
import time
import threading
import ctypes
import inspectdef sayHello():for i in range(10):print("hello")time.sleep(1)def _async_raise(tid, exctype):"""raises the exception, performs cleanup if needed"""tid = ctypes.c_long(tid)if not inspect.isclass(exctype):exctype = type(exctype)res = ctypes.pythonapi.PyThreadState_SetAsyncExc(tid, ctypes.py_object(exctype))if res == 0:raise ValueError("invalid thread id")elif res != 1:# """if it returns a number greater than one, you're in trouble,# and you should call it again with exc=NULL to revert the effect"""ctypes.pythonapi.PyThreadState_SetAsyncExc(tid, None)raise SystemError("PyThreadState_SetAsyncExc failed")def stop_thread(thread):_async_raise(thread.ident, SystemExit)if __name__ == '__main__':# sayHello()t = threading.Thread(target=sayHello, args=())t.setDaemon(False) # 主线程结束后不停止子线程t.start()for i in range(3):print(t.is_alive())time.sleep(1)# t.join()print("over")

输出结果为：

hello
True
True
hello
True
hello
hello
over
hello
hello
hello
hello
hello
hello

可以看到主线程结束时，打印出over，之后子线程还在继续打印hello

修改代码：

'''
遇到问题没人解答？小编创建了一个Python学习交流QQ群：778463939
寻找有志同道合的小伙伴，互帮互助,群里还有不错的视频学习教程和PDF电子书！
'''
import time
import threading
import ctypes
import inspectdef sayHello():for i in range(10):print("hello")time.sleep(1)def _async_raise(tid, exctype):"""raises the exception, performs cleanup if needed"""tid = ctypes.c_long(tid)if not inspect.isclass(exctype):exctype = type(exctype)res = ctypes.pythonapi.PyThreadState_SetAsyncExc(tid, ctypes.py_object(exctype))if res == 0:raise ValueError("invalid thread id")elif res != 1:# """if it returns a number greater than one, you're in trouble,# and you should call it again with exc=NULL to revert the effect"""ctypes.pythonapi.PyThreadState_SetAsyncExc(tid, None)raise SystemError("PyThreadState_SetAsyncExc failed")def stop_thread(thread):_async_raise(thread.ident, SystemExit)if __name__ == '__main__':# sayHello()t = threading.Thread(target=sayHello, args=())t.setDaemon(False) # 主线程结束后不停止子线程t.start()for i in range(3):print(t.is_alive())time.sleep(1)t.join()print("over")

输出结果为：

hello
True
hello
True
True
hello
hello
hello
hello
hello
hello
hello
hello
over

可以看到设置t.join()方法之后，主线程要等待t这个线程结束之后，才能继续，也就是等hello打印完之后才打印over。

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