Python inter-process communication Queue instance parsing, pythonqueue

Python inter-process communication Queue instance parsing, pythonqueue

This article mainly studies the Python process-to-process communication Queue examples, as detailed below.

1. Queue usage:

• Queue. qsize (): returns the number of messages contained in the current Queue;
• Queue. empty (): If the Queue is empty, True is returned; otherwise, False is returned;
• Queue. full (): If the Queue is full, True is returned; otherwise, False is returned;
• Queue. get (): gets a message in the Queue and removes it from the Queue. The parameter timeout period can be passed.
• Queue. get_nowait (): equivalent to Queue. get (False). If the value is not obtained, an exception is triggered: Empty;
• Queue. put (): adds a value to the sequence to pass the parameter timeout period.
• Queue. put_nowait (): equivalent to Queue. get (False). When the Queue is Full, an error is returned: Full.
  

2. Queue instance:

Come, the code above:

#! /Usr/bin/env python3import timefrom multiprocessing import Process, Queueq = Queue () # create a Queue. If no number is passed, there is no limit to the number of queues for I in range (11): q. put (I) def A (): while 1: try: num = q. get_nowait () print ('process A, retrieve the number: % d' % num) time. sleep (1) failed T: breakdef B (): while 1: try: num = q. get_nowait () print ('process B, retrieve the number: % d' % num) time. sleep (1) failed T: breakp1 = Process (target = A) p2 = Process (target = B) p1.start () p2.start ()

This program adds 10 numbers to the queue and then uses two processes to retrieve them.

Running result:

I am process A, and the number is 0.
I am process B and retrieve the number: 1
I am process A and retrieve the number: 2
I am process B, and the number is 3.
I am process A and retrieve the number: 4
I am process B, and the number is 5.
I am process B, and the number is 6.
I am process A and retrieve the number: 7
I am process B, and the number is 8.
I am process A and retrieve the number: 9
I am process B, and the number is 10.

3. When using the process Pool, the Queue will encounter an error. You need to use Manager. Queue:

Code on

#! /Usr/bin/env python3import timefrom multiprocessing import Pool, Manager, Queueq = Manager (). queue () for I in range (11): q. put (I) def A (I): num = q. get_nowait () print ('I am a process % d, retrieve the number: % d' % (I, num) time. sleep (1) pool = Pool (3) for I in range (10): pool. apply_async (A, (I,) pool. close () pool. join ()

Running result:

I am process 1 and retrieve the number: 0
I am a process 0 and retrieve the number: 1
I am process 2 and retrieve the number: 2
I am process 4 and retrieve the number: 3
I am process 3 and retrieve the number: 4
I am process 5, and retrieve the number: 5
I am process 6, and the number is 6.
I am a process 7 and retrieve the number: 7
I am PROCESS 8 and retrieve the number: 8
I am process 9 and retrieve the number: 9

If you change Manager (). Queue () to Queue () directly, there may be resource confusion and a lack of processes.

4. The main Process defines a variable of the Queue type and transmits it as the args parameter of the Process to the sub-Process processA and processB. The two processes write data to the Queue and read data.

import timefrom multiprocessing import Process,QueueMSG_QUEUE = Queue(5)def startA(msgQueue):  while True:    if msgQueue.empty() > 0:      print 'queue is empty %d' % (msgQueue.qsize())    else:      msg = msgQueue.get()      print 'get msg %s' % (msg,)    time.sleep(1)def startB(msgQueue):  while True:    msgQueue.put('hello world')    print 'put hello world queue size is %d' % (msgQueue.qsize(),)    time.sleep(3)if __name__ == '__main__':  processA = Process(target=startA,args=(MSG_QUEUE,))  processB = Process(target=startB,args=(MSG_QUEUE,))  processA.start()  print 'processA start..'  processB.start()  print 'processB start..'

The printed result is as follows:

C: \ Python27 \ python.exe E:/outofmemory/test/queuetest. py
ProcessA start ..
ProcessB start ..
Queue is empty 0
Put hello world queue size is 1
Get msg hello world
Queue is empty 0
Queue is empty 0
Put hello world queue size is 1
Get msg hello world
Queue is empty 0
Queue is empty 0
Put hello world queue size is 1

Summary

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