看一下线程的setDaemon()方法
import time import threading import ctypes import inspect def 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:
import time import threading import ctypes import inspect def 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
import time import threading import ctypes import inspect def 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:
import time import threading import ctypes import inspect def 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。