看一下线程的setDaemon()方法

importtimeimportthreadingimportctypesimportinspectdefsayHello():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 notinspect.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")defstop_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：

importtimeimportthreadingimportctypesimportinspectdefsayHello():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 notinspect.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")defstop_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

importtimeimportthreadingimportctypesimportinspectdefsayHello():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 notinspect.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")defstop_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：

importtimeimportthreadingimportctypesimportinspectdefsayHello():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 notinspect.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")defstop_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。