如何在一个子进程完成时终止运行中的子进程（多进程）

Question

我遇到了一个关于多进程的问题：

class PythonHelper(object):
    @staticmethod
    def run_in_parallel(*functions):
        processes=list()
        for function in functions:
            process=Process(target=function)
            process.start()
            processes.append(process)
        for process in processes:
            process.join()

上面的静态方法是我用来同时运行几个函数的（把它们放在一个进程里）。一切都很好，直到我需要在一个“子进程”结束时强制终止整个进程。

举个例子：

from PythonHelper import PythonHelper as ph
from Recorder import Recorder

class Logger(object):

    def run_recorder_proc(self):
        rec=Recorder()
        rec.record_video()

    def run_printer_proc(self):
    #hypothetical function: execution takes a long time
        for i in range(9000000):
            print("number: {}".format(i))

    def run_logger(self):
        ph.run_in_parallel(self.run_printer_proc,self.run_recorder_proc)

self.run_printer_proc 和 self.run_recorder_proc 是我的子进程。怎么才能在其中一个完成时“杀掉”剩下的子进程呢？

---

编辑：

完整的源代码：

class PythonHelper(object):
    @staticmethod
    #with your fix
    def run_in_parallel(*functions):
        processes={}
        for function in functions:
            process=Process(target=function)
            process.start()
            processes[process.pid]=process
        # wait for any process to complete
        pid, status = os.waitpid(-1, 0)
        # one process terminated
        # join it
        processes[pid].join()
        del processes[pid]
        # terminate the rest
        for process in processes.values():
            process.terminate()
        for process in processes.values():
            process.join()


class Logger(object):
    def run_numbers_1(self):
        for i in range(900000):
            print("number: {}".format(i))
    def run_numbers_2(self):
        for i in range(100000):
            print("number: {}".format(i))
    def run_logger(self):
        ph.run_in_parallel(self.run_numbers_1,self.run_numbers_2)

if __name__=="__main__":
    logger=Logger()
    logger.run_logger()

根据上面的例子，我想在run_numbers_2完成时强制终止run_numbers_1。

Answer 1

你可以通过稍微修改一下 run_in_parallel() 来实现这个功能：

def run_in_parallel(*functions):
    processes={}
    for function in functions:
        process=Process(target=function)
        process.start()
        processes[process.pid]=process
    # wait for any process to complete
    pid, status = os.waitpid(-1, 0) 
    # one process terminated
    # join it
    processes[pid].join()
    del processes[pid]
    # terminate the rest
    for process in processes.itervalues():
        process.terminate()
    for process in processes.itervalues():
        process.join()

[更新] 根据你提供的完整代码，这里有一个可以正常工作的例子。它使用了 Event 对象，而不是容易出问题的 os.waitpid()，这个对象会在其他进程完成时被设置：

from multiprocessing import Process, Event

class MyProcess(Process):
    def __init__(self, event, *args, **kwargs):
        self.event = event
        Process.__init__(self, *args, **kwargs)

    def run(self):
        Process.run(self)
        self.event.set()

class PythonHelper(object):
    @staticmethod
    #with your fix
    def run_in_parallel(*functions):
        event = Event()
        processes=[]
        for function in functions:
            process=MyProcess(event, target=function)
            process.start()
            processes.append(process)
        # wait for any process to complete
        event.wait()
        # one process completed
        # terminate all child processes
        for process in processes:
            process.terminate()
        for process in processes:
            process.join()


class Logger(object):
    def run_numbers_1(self):
        for i in range(90000):
            print("1 number: {}".format(i))
    def run_numbers_2(self):
        for i in range(10000):
            print("2 number: {}".format(i))
    def run_logger(self):
        PythonHelper.run_in_parallel(self.run_numbers_1,self.run_numbers_2)

if __name__=="__main__":
    logger=Logger()
    logger.run_logger()