This article examines the main examples related to Python inter-process communication Queue as follows.
Usage:
- (): Returns the number of messages the current queue contains;
- (): Returns True if the queue is empty, and False otherwise;
- (): If the queue is full, return True, and vice versa False;
- ():Get a message in the queue and then remove it from the queue, with a passable timeout duration.
- Queue.get_nowait(): quite (False), triggers an exception when value is not fetched: Empty;
- (): Add a value to the array, pass a reference to the timeout duration.
- Queue.put_nowait(): equivalent to (False), error when queue is full: Full.
Usage Example:
Come on, get on the code:
#!/usr/bin/env python3
import time
from multiprocessing import Process,Queue
q = Queue() #Create queue, do not pass a number to indicate an unlimited number of queues
for i in range(11):
(i)
def A():
while 1:
try:
num = q.get_nowait()
print('I am process A, take out number: %d'%num)
(1)
except :
break
def B():
while 1:
try:
num = q.get_nowait()
print('This is process B, take out number: %d'%num)
(1)
except :
break
p1 = Process(target = A)
p2 = Process(target = B)
()
()
This program is to add 10 numbers to the queue and then use 2 processes to take them out.
Run results:
I'm process A. Take out the number: 0.
I'm process B. Take out the number: 1.
I'm process A. Take out the number: 2.
I'm process B. Take out the number: 3.
I'm process A. Take out the number: 4.
I'm process B. Take out the number: 5.
I'm process B. Take out the number: 6.
I'm process A. Take out the number: 7.
I'm process B. Take out the number: 8.
I'm process A. Take out the number: 9.
I'm process B. Take out the number: 10.
3. When using the process pool Pool, Queue will error out and need to be used:
coding
#!/usr/bin/env python3
import time
from multiprocessing import Pool,Manager,Queue
q = Manager().Queue()
for i in range(11):
(i)
def A(i):
num = q.get_nowait()
print('I am process %d, take out number: %d'%(i,num))
(1)
pool = Pool(3)
for i in range(10):
pool.apply_async(A,(i,))
()
()
Run results:
I'm process 1, take out the number: 0.
I'm process 0, take out the number: 1.
I'm process 2. Take out the number: 2.
I'm process 4, take out the number: 3.
I'm process 3, take out number 4.
I'm process 5, take out the number: 5.
I'm process 6. Take out the number: 6.
I'm process 7, take out the number: 7.
I'm process 8, take out the number: 8.
I'm process 9, take out the number: 9.
When replacing Manager().Queue() directly with Queue(), there may be resource confusion and missing processes.
4. The main process defines a variable of type Queue and passes it as the args parameter of Process to the sub-processes processA and processB, and one of the two processes writes data to the queue, and the other reads data.
import time
from multiprocessing import Process,Queue
MSG_QUEUE = Queue(5)
def startA(msgQueue):
while True:
if () > 0:
print 'queue is empty %d' % (())
else:
msg = ()
print 'get msg %s' % (msg,)
(1)
def startB(msgQueue):
while True:
('hello world')
print 'put hello world queue size is %d' % ((),)
(3)
if __name__ == '__main__':
processA = Process(target=startA,args=(MSG_QUEUE,))
processB = Process(target=startB,args=(MSG_QUEUE,))
()
print 'processA start..'
()
print 'processB start..'
It prints as follows:
C:\Python27\ E:/outofmemory/test/queuetest/
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
summarize
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