如何在Python中的两个独立进程之间来回交换数据

Question

问题

有两个独立的进程并行运行，我希望它们能够来回通信

代码说明

代码在Python2.7中。在我的精简脚本中，我使用队列进行进程间通信。进程p1将数据放入队列中。进程p2从队列中获取数据，并对数据进行处理。然后进程p2将修改后的数据放回队列，最后进程p1从队列中取回修改后的数据。修改后的数据必须返回到进程p1，因为该进程实际上是一个发送/接收请求的eventlet服务器

代码

#!/usr/bin/python2.7 python2.7
# -*- coding: utf-8 -*-
# script for back-and-forth data exchange between processes

# common modules
import os
import sys
import time
from multiprocessing import Process
from multiprocessing import Queue
from datetime import datetime

someData = {}

class Load():
    def post(self):
        timestamp = str(datetime.now())
        someData = {"process":"p1","class":"Load()","method":"post()","timestamp":timestamp}
        queue1.put(someData)        # put into queue
        print "#20 process 1: put in queue1 =>", someData
        time.sleep(3)

        while True:     # queue1 checking loop, comment out the loop if use time.sleep only
            if queue1.empty() == False:
                timestamp = str(datetime.now())
                res = queue1.get()
                res = {"process":"p1","class":"Load()","method":"post()","timestamp":timestamp}
                print "#28 get from queue1 =>", res
                break
            else:
                print "#31 queue1 empty"
                time.sleep(1)

        # while True:       # queue2 checking loop
        #   if queue2.empty() == False:
        #       timestamp = str(datetime.now())
        #       res = queue2.get()
        #       res = {"process":"p1","class":"Load()","method":"post()","timestamp":timestamp}
        #       print "#39 get from queue2 =>", res
        #       break
        #   else:
        #       print "#42 queue2 empty"
        #       time.sleep(1)

class Unload():
    def get(self):
        try:
            if queue1.empty() == False:
                data = queue1.get()     # retrieve package from queue
                #queue1.close()
                #queue1.join_thread()
                timestamp = str(datetime.now())
                data = {"process":"p2","class":"Unload()","method":"get()","timestamp":timestamp} 
                print "#54 process 2: get from queue1 =>", data
                self.doSomething(data)  # call method
            else:
                print "#57 queue1 empty"
                pass
        except:
            print "#60 queue1 error"
            pass

    def doSomething(self, data):
        time.sleep(3)
        timestamp = str(datetime.now())
        someData = {"process":"p2","class":"Unload()","method":"doSomething()","timestamp":timestamp}
        self.someData = someData
        print "#68 process 2: do something =>", someData
        self.put()

    def put(self):
        time.sleep(3)
        timestamp = str(datetime.now())
        self.someData = {"process":"p2","class":"Unload()","method":"put()","timestamp":timestamp}
        print "#75 process 2: put back in queue1 =>", self.someData
        res = self.someData
        queue1.put(res)
        #print "#78 process 2: put back in queue2 =>", self.someData
        #res = self.someData
        #queue2.put(res)
        #queue2.close()
        #queue2.join_thread()

# main 
if __name__ == '__main__':

    queue1 = Queue()
    #queue2 = Queue()

    global p1, p2
    p1 = Process(target=Load().post(), args=(queue1,))      # process p1
    #p1 = Process(target=Load().post(), args=(queue1,queue2,))
    p1.daemon = True
    p1.start() 

    p2 = Process(target=Unload().get(), args=(queue1,))     # process p2
    #p2 = Process(target=Unload().get(), args=(queue1,queue2,))
    p2.start()
    p2.join()

问题 我已经检查了这方面的其他资源，但它们都涉及单向沟通。下面是资源列表

1. use-get-nowait-in-python-without-raising-empty-exception
2. in-python-how-do-you-get-data-back-from-a-particular-process-using-multiprocess
3. how-to-use-multiprocessing-queue-with-lock
4. multiprocessing module supports locks
5. thread-that-i-can-pause-and-resume
6. exchange-data-between-two-python-processes

如何让process1等待并从process2检索修改后的数据？我应该考虑另一种方法来处理进程之间的通信吗？例如，管道，ZNOMQ？

尝试1：在进程1中不使用while循环而使用time.sleep（） 仅使用time.sleep，数据在队列中上下移动，但永远不会到达进程1中的最终目的地。到目前为止一切都很好，但最后一步还没有完成。结果如下

#20 process 1: put in queue1 => {'process': 'p1', 'timestamp': '2020-02-23 11:40:30.234466', 'class': 'Load()', 'method': 'post()'}
#54 process 2: get from queue1 => {'process': 'p2', 'timestamp': '2020-02-23 11:40:33.239113', 'class': 'Unload()', 'method': 'get()'}
#68 process 2: do something => {'process': 'p2', 'timestamp': '2020-02-23 11:40:36.242500', 'class': 'Unload()', 'method': 'doSomething()'}
#75 process 2: put back in queue1 => {'process': 'p2', 'timestamp': '2020-02-23 11:40:39.245856', 'class': 'Unload()', 'method': 'put()'}

尝试2：在进程1中使用while循环 通过while循环检查队列，数据进入队列后立即被捕获，它们永远不会到达进程2。结果如下

#20 process 1: put in queue1 => {'process': 'p1', 'timestamp': '2020-02-23 11:46:14.606356', 'class': 'Load()', 'method': 'post()'}
#28 get from queue1 => {'process': 'p1', 'timestamp': '2020-02-23 11:46:17.610202', 'class': 'Load()', 'method': 'post()'}
#57 queue1 empty

尝试3：使用两个队列 使用两个队列：队列1从process1到process2，队列2从process2到process1。数据进入队列1，但不返回队列2，它们神秘地消失了。结果如下

#20 process 1: put in queue1 => {'process': 'p1', 'timestamp': '2020-02-23 11:53:39.745177', 'class': 'Load()', 'method': 'post()'}
#42 queue2 empty

----更新20200224：尝试4、5和6---------------------------------------------------------------------

尝试4:使用manager.Queue（）的两个队列

在manager.Queue（）中使用两个队列：队列1从process1到process2，队列2从process2到process1。数据进入队列1，但不返回队列2，它们再次神秘地消失。代码和结果如下所示

尝试4的代码： #!/usr/bin/python2.7 python2.7 #编码：utf-8-- #用于序列化进程间数据交换的脚本

# common modules
import os
import sys
import time
import multiprocessing
from multiprocessing import Process
from multiprocessing import Queue
from multiprocessing import Manager
from datetime import datetime

someData = {}
manager = multiprocessing.Manager()
queue1 = manager.Queue()
queue2 = manager.Queue()

class Load():
    def post(self):
        timestamp = str(datetime.now())
        someData = {"process":"p1","class":"Load()","method":"post()","timestamp":timestamp}
        queue1.put(someData)        # put into queue
        print "#20 process 1: put in queue1 =>", someData
        time.sleep(3)

        # while True:       # queue1 checking loop
        #   if queue1.empty() == False:
        #       timestamp = str(datetime.now())
        #       res = queue1.get()
        #       res = {"process":"p1","class":"Load()","method":"post()","timestamp":timestamp}
        #       print "#28 get from queue1 =>", res
        #       break
        #   else:
        #       print "#31 queue1 empty"
        #       time.sleep(1)

        while True:     # queue2 checking loop
            if queue2.empty() == False:
                timestamp = str(datetime.now())
                res = queue2.get()
                res = {"process":"p1","class":"Load()","method":"post()","timestamp":timestamp}
                print "#39 get from queue2 =>", res
                break
            else:
                print "#42 queue2 empty"
                time.sleep(1)

class Unload():
    def get(self):
        try:
            if queue1.empty() == False:
                data = queue1.get()     # retrieve package from queue
                #queue1.close()
                #queue1.join_thread()
                timestamp = str(datetime.now())
                data = {"process":"p2","class":"Unload()","method":"get()","timestamp":timestamp} 
                print "#54 process 2: get from queue1 =>", data
                self.doSomething(data)  # call method
            else:
                print "#57 queue1 empty"
                pass
        except:
            print "#60 queue1 error"
            pass

    def doSomething(self, data):
        time.sleep(3)
        timestamp = str(datetime.now())
        someData = {"process":"p2","class":"Unload()","method":"doSomething()","timestamp":timestamp}
        self.someData = someData
        print "#68 process 2: do something =>", someData
        self.put()

    def put(self):
        time.sleep(3)
        timestamp = str(datetime.now())
        self.someData = {"process":"p2","class":"Unload()","method":"put()","timestamp":timestamp}
        res = self.someData
        #print "#75 process 2: put back in queue1 =>", self.someData
        #queue1.put(res)
        print "#78 process 2: put back in queue2 =>", self.someData
        queue2.put(res)
        #queue2.close()
        #queue2.join_thread()

# main 
if __name__ == '__main__':

    manager = multiprocessing.Manager()
    queue1 = manager.Queue()
    queue2 = manager.Queue()

    global p1, p2
    #p1 = Process(target=Load().post(), args=(queue1,))     # process p1
    p1 = Process(target=Load().post(), args=(queue1,queue2,))
    p1.daemon = True
    p1.start() 

    #p2 = Process(target=Unload().get(), args=(queue1,))        # process p2
    p2 = Process(target=Unload().get(), args=(queue1,queue2,))
    p2.start()
    p2.join()

尝试4的结果：

#20 process 1: put in queue1 => {'process': 'p1', 'timestamp': '2020-02-24 13:06:17.687762', 'class': 'Load()', 'method': 'post()'}
#42 queue2 empty

尝试5:与manager.queue（）一起使用一个队列 在manager.queue（）中使用一个队列：queue1从process1到process2，queue1从process2返回到process1。数据进入队列1，但随后立即被捕获，它们永远不会到达进程2。代码结果如下所示

尝试5的代码：

#!/usr/bin/python2.7 python2.7
# -*- coding: utf-8 -*-
# script for serialized interprocess data exchange

# common modules
import os
import sys
import time
import multiprocessing
from multiprocessing import Process
from multiprocessing import Queue
from multiprocessing import Manager
from datetime import datetime

someData = {}
manager = multiprocessing.Manager()
queue1 = manager.Queue()
#queue2 = manager.Queue()

class Load():
    def post(self):
        timestamp = str(datetime.now())
        someData = {"process":"p1","class":"Load()","method":"post()","timestamp":timestamp}
        queue1.put(someData)        # put into queue
        print "#25 process 1: put in queue1 =>", someData
        time.sleep(3)

        while True:     # queue1 checking loop
            if queue1.empty() == False:
                timestamp = str(datetime.now())
                res = queue1.get()
                res = {"process":"p1","class":"Load()","method":"post()","timestamp":timestamp}
                print "#33 get from queue1 =>", res
                break
            else:
                print "#36 queue1 empty"
                time.sleep(1)

        # while True:       # queue2 checking loop
        #   if queue2.empty() == False:
        #       timestamp = str(datetime.now())
        #       res = queue2.get()
        #       res = {"process":"p1","class":"Load()","method":"post()","timestamp":timestamp}
        #       print "#44 get from queue2 =>", res
        #       break
        #   else:
        #       print "#47 queue2 empty"
        #       time.sleep(1)

class Unload():
    def get(self):
        try:
            if queue1.empty() == False:
                data = queue1.get()     # retrieve package from queue
                #queue1.close()
                #queue1.join_thread()
                timestamp = str(datetime.now())
                data = {"process":"p2","class":"Unload()","method":"get()","timestamp":timestamp} 
                print "#59 process 2: get from queue1 =>", data
                self.doSomething(data)  # call method
            else:
                print "#62 queue1 empty"
                pass
        except:
            print "#65 queue1 error"
            pass

    def doSomething(self, data):
        time.sleep(3)
        timestamp = str(datetime.now())
        someData = {"process":"p2","class":"Unload()","method":"doSomething()","timestamp":timestamp}
        self.someData = someData
        print "#73 process 2: do something =>", someData
        self.put()

    def put(self):
        time.sleep(3)
        timestamp = str(datetime.now())
        self.someData = {"process":"p2","class":"Unload()","method":"put()","timestamp":timestamp}
        res = self.someData
        print "#81 process 2: put back in queue1 =>", self.someData
        queue1.put(res)
        #print "#83 process 2: put back in queue2 =>", self.someData
        #queue2.put(res)
        #queue2.close()
        #queue2.join_thread()

# main 
if __name__ == '__main__':

    manager = multiprocessing.Manager()
    queue1 = manager.Queue()
    #queue2 = manager.Queue()

    global p1, p2
    p1 = Process(target=Load().post(), args=(queue1,))      # process p1
    #p1 = Process(target=Load().post(), args=(queue1,queue2,))
    p1.daemon = True
    p1.start() 

    p2 = Process(target=Unload().get(), args=(queue1,))     # process p2
    #p2 = Process(target=Unload().get(), args=(queue1,queue2,))
    p2.start()
    p2.join()

尝试5的结果：

#25 process 1: put in queue1 => {'process': 'p1', 'timestamp': '2020-02-24 14:08:13.975886', 'class': 'Load()', 'method': 'post()'}
#33 get from queue1 => {'process': 'p1', 'timestamp': '2020-02-24 14:08:16.980382', 'class': 'Load()', 'method': 'post()'}
#62 queue1 empty

尝试6：使用队列超时

正如我建议的那样，我试图纠正队列超时。该方法同样是队列1从process1到process2，队列2从process2到process1。数据进入队列1，但不返回队列2，它们再次神秘地消失。代码和结果如下所示

尝试6的代码：

#!/usr/bin/python2.7 python2.7
# -*- coding: utf-8 -*-
# script for serialized interprocess data exchange

# common modules
import os
import sys
import time
import uuid
import Queue
#from Queue import Empty
import multiprocessing
from multiprocessing import Process
#from multiprocessing import Queue
from datetime import datetime

someData = {}

class Load():
    def post(self):
        timestamp = str(datetime.now())
        someData = {"process":"p1","class":"Load()","method":"post()","timestamp":timestamp}
        queue1.put(someData)        # put into queue
        print "#24 process 1: put in queue1 =>", someData
        time.sleep(3)

        # while True:       # queue1 checking loop
        #   if queue1.empty() == False:
        #       timestamp = str(datetime.now())
        #       res = queue1.get()
        #       res = {"process":"p1","class":"Load()","method":"post()","timestamp":timestamp}
        #       print "#33 get from queue1 =>", res
        #       break
        #   else:
        #       print "#36 queue1 empty"
        #       time.sleep(1)

        while True:     # queue2 checking loop
            try:
                someData = queue2.get(True,1)
                timestamp = str(datetime.now())
                someData = {"process":"p1","class":"Load()","method":"post()","timestamp":timestamp}
                print "#43 process 1: got from queue2 =>", someData
                break
            except Queue.Empty:
                print "#46 process1: queue2 empty"
                continue

class Unload():
    def get(self):
        while True:     # queue2 checking loop
            try:
                someData = queue1.get(True,1)
                timestamp = str(datetime.now())
                someData = {"process":"p2","class":"Unload()","method":"get()","timestamp":timestamp} 
                print "#56 process2: got from queue1 =>", someData
                break
            except Queue.Empty:
                print "#59 process2: queue1 empty"
                continue
        self.doSomething(someData)  # call method

    def doSomething(self, data):
        time.sleep(3)
        timestamp = str(datetime.now())
        someData = {"process":"p2","class":"Unload()","method":"doSomething()","timestamp":timestamp}
        self.someData = someData
        print "#68 process2: do something =>", someData
        self.put(someData)

    def put(self,data):
        time.sleep(3)
        timestamp = str(datetime.now())
        self.someData = {"process":"p2","class":"Unload()","method":"put()","timestamp":timestamp}
        someData = self.someData
        #print "#81 process 2: put back in queue1 =>", self.someData
        #queue1.put(res)
        print "#78 process2: put back in queue2 =>", someData
        queue2.put(someData)


# main 
if __name__ == '__main__':

    queue1 = multiprocessing.Queue()
    queue2 = multiprocessing.Queue()

    global p1, p2
    #p1 = Process(target=Load().post(), args=(queue1,))     # process p1
    p1 = Process(target=Load().post(), args=(queue1,queue2,))
    p1.daemon = True
    p1.start() 

    #p2 = Process(target=Unload().get(), args=(queue1,))        # process p2
    p2 = Process(target=Unload().get(), args=(queue1,queue2,))
    p2.start()
    p2.join()

尝试6的结果：

#24 process 1: put in queue1 => {'process': 'p1', 'timestamp': '2020-02-24 18:14:46.435661', 'class': 'Load()', 'method': 'post()'}
#46 process1: queue2 empty

注意：当我在没有类的情况下使用它时，建议的方法是有效的。代码如下：

import uuid
import multiprocessing
from multiprocessing import Process
import Queue


def load(que_in, que_out):
    request = {"id": uuid.uuid4(), "workload": "do_stuff", }
    que_in.put(request)
    print("load: sent request {}: {}".format(request["id"], request["workload"]))
    while True:
        try:
            result = que_out.get(True, 1)
        except Queue.Empty:
            continue
        print("load: got result {}: {}".format(result["id"], result["result"]))


def unload(que_in, que_out):
    def processed(request):
        return {"id": request["id"], "result": request["workload"] + " processed", }
    while True:
        try:
            request = que_in.get(True, 1)
        except Queue.Empty:
            continue
        print("unload: got request {}: {}".format(request["id"], request["workload"]))
        result = processed(request)
        que_out.put(result)
        print("unload: sent result {}: {}".format(result["id"], result["result"]))


    # main
if __name__ == '__main__':

    que_in = multiprocessing.Queue()
    que_out = multiprocessing.Queue()

    p1 = Process(target=load, args=(que_in, que_out))      # process p1
    p1.daemon = True
    p1.start()

    p2 = Process(target=unload, args=(que_in, que_out))     # process p2
    p2.start()
    p2.join()

----更新20200225:尝试7-------------------------------------------------------------------------------

尝试7：使用一个队列，在不同类别中出现队列超时（工作）

在这次尝试中，我在不同类的方法之间使用了一个共享队列，并更正了超时。数据从process1传输到proces在共享队列中从进程2返回到进程1。在这次尝试中，数据传输正确。代码和结果如下所示

尝试7的代码：

import uuid
import multiprocessing
from multiprocessing import Process
import Queue

class Input():
    def load(self, shared_queue):
        request = {"id": uuid.uuid4(), "workload": "do_stuff", }
        shared_queue.put(request)
        print("load: sent request {}: {}".format(request["id"], request["workload"]))
        while True:
            try:
                result = shared_queue.get(True, 1)
            except Queue.Empty:
                continue
            print("load: got result {}: {}".format(result["id"], result["result"]))
            break

class Output():
    def unload(self, shared_queue):
        def processed(request):
            return {"id": request["id"], "result": request["workload"] + " processed", }
        while True:
            try:
                request = shared_queue.get(True, 1)
            except Queue.Empty:
                continue
            print("unload: got request {}: {}".format(request["id"], request["workload"]))
            result = processed(request)
            shared_queue.put(result)
            print("unload: sent result {}: {}".format(result["id"], result["result"]))


    # main
if __name__ == '__main__':

    shared_queue = multiprocessing.Queue()
    up = Input()
    down = Output()

    p1 = Process(target=up.load, args=(shared_queue,))      # process p1
    p1.daemon = True
    p1.start()


    p2 = Process(target=down.unload, args=(shared_queue,))     # process p2
    p2.start()

    p1.join()
    p2.join()

尝试7的结果：

load: sent request a461357a-b39a-43c4-89a8-a77486a5bf45: do_stuff
unload: got request a461357a-b39a-43c4-89a8-a77486a5bf45: do_stuff
unload: sent result a461357a-b39a-43c4-89a8-a77486a5bf45: do_stuff processed
load: got result a461357a-b39a-43c4-89a8-a77486a5bf45: do_stuff processed

Answer 1

我想你只是错过了排队时间

try:
    result = que_out.get(True, 1)
except queue.Empty:
    continue

此简化示例可能会帮助您：

import uuid
from multiprocessing import Process
from multiprocessing import Queue
import queue


def load(que_in, que_out):
    request = {"id": uuid.uuid4(), "workload": "do_stuff", }
    que_in.put(request)
    print("load: sent request {}: {}".format(request["id"], request["workload"]))
    while True:
        try:
            result = que_out.get(True, 1)
        except queue.Empty:
            continue
        print("load: got result {}: {}".format(result["id"], result["result"]))


def unload(que_in, que_out):

    def processed(request):
        return {"id": request["id"], "result": request["workload"] + " processed", }

    while True:
        try:
            request = que_in.get(True, 1)
        except queue.Empty:
            continue
        print("unload: got request {}: {}".format(request["id"], request["workload"]))
        result = processed(request)
        que_out.put(result)
        print("unload: sent result {}: {}".format(result["id"], result["result"]))

    # main
if __name__ == '__main__':

    que_in = Queue()
    que_out = Queue()

    p1 = Process(target=load, args=(que_in, que_out))      # process p1
    p1.daemon = True
    p1.start()

    p2 = Process(target=unload, args=(que_in, que_out))     # process p2
    p2.start()
    p2.join()

输出

load: sent request d9894e41-3e8a-4474-9563-1a99797bc722: do_stuff
unload: got request d9894e41-3e8a-4474-9563-1a99797bc722: do_stuff
unload: sent result d9894e41-3e8a-4474-9563-1a99797bc722: do_stuff processed
load: got result d9894e41-3e8a-4474-9563-1a99797bc722: do_stuff processed