基于python生成器封装的协程类

Posted 2022-12-06 OshynSong

自从python2.2提供了yield关键字之后，python的生成器的很大一部分用途就是可以用来构建协同程序，能够将函数挂起返回中间值并能从上次离开的地方继续执行。python2.5的时候，这种生成器更加接近完全的协程，因为提供了将值和异常传递回到一个继续执行的函数中，当等待生成器的时候，生成器能返回控制。

python提供的生成器设施：

• yield：能够将自己挂起，并提供一个返回值给等待方
• send：唤起一个被挂起的生成器，并能够传递一个参数，可以在生成器中抛出异常
• next：本质上相当于send(None)，对每个生成器的第一次调用必须不能传递参数
• close：主动退出一个生成器

python封装

虽然python3提供了asyncio这样的异步IO库，而且也有greenlet等其他协程库，但目前的需求并不是实际的网络IO并发操作，而是需要模拟状态机的运行，因此使用协程可以很方便的模拟，并加入认为的控制，下面是封装的一个python类。

class Coroutine(object):

    """ Base class of the general coroutine object """

    STATE_RUNNING = 0
    STATE_WAITING = 1
    STATE_CLOSING = 2

    def __init__(self):
        self.state = Coroutine.STATE_WAITING
        self.started = False
        self.args = None
        self.routine = self._co()

    def _co(self):
        self.ret = None
        while True:
            self.args = yield self.ret
            if not self.started:
                self.started = True
                continue
            else:
                self.state = Coroutine.STATE_RUNNING
                self.ret = self.run(self.args)
            if self.state == Coroutine.STATE_CLOSING:
                break
            self.state = Coroutine.STATE_WAITING

    def start(self):
        """ Start the generator """
        if self.routine is None:
            raise RuntimeError('NO task to start running!')
        self.started = True
        self.routine.next()

    def finish(self):
        """ Finish the execution of this routine """
        self.state = Coroutine.STATE_CLOSING
        self.routine.close()

    def run(self, args):
        """ The runing method to be executed every once time"""
        raise NotImplementedError

    def execute(self, arg_obj):
        """ Awake this routine to execute once time """
        return self.routine.send(arg_obj)

基于上述封装，下面实现了一个协同的生产者消费者示例：

class ProducerCoroutine(Coroutine):

    """ The Producer concrete coroutine """

    def __init__(self, cnsmr):
        if not isinstance(cnsmr, Coroutine):
            raise RuntimeError('Consumer is not a Coroutine object')
        self.consumer = cnsmr
        self.consumer.start()
        super(ProducerCoroutine, self).__init__()

    def run(self, args):
        print 'produce ', args
        ret = self.consumer.execute(args)
        print 'consumer return:', ret

    def __call__(self, args):
        """ Custom method for the specific logic """
        self.start()
        while len(args) > 0:
            p = args.pop()
            self.execute(p)
        self.finish()


class ConsumerCoroutine(Coroutine):

    """ The Consumer concrete coroutine """

    def __init__(self):
        super(ConsumerCoroutine, self).__init__()

    def run(self, args):
        print 'consumer get args: ', args
        return 'hahaha' + repr(args)

运行结果如下：

produce  4
consumer get args:  4
consumer return: hahaha4
produce  3
consumer get args:  3
consumer return: hahaha3
produce  2
consumer get args:  2
consumer return: hahaha2
produce  1
consumer get args:  1
consumer return: hahaha1
produce  0
consumer get args:  0
consumer return: hahaha0