Method Name:
qsize
Method Signature:
qsize()
Return Value:
int
Parameters:
Not Applicable
Method Overview:
- Returns the “approximate” size of the Queue. The returned size is approximate because the use cases involve multiprocessing and multithreading scenarios.
- One of the following workarounds can be used to resolve the issue of qsize() returning “approximate size" of the Queue,
- Using a known maximum queue size
- Using the terminal condition/guardian condition/sentinel variable
Example:
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import multiprocessing
# Reader process def writerProc(messageQueue, maxQueueSize): for i in range(1, maxQueueSize): messageQueue.put("Message%d"%i)
# Writer process def readerProc(messageQueue, maxQueueSize): reapCount = 0
#while messageQueue.qsize() - returns only approximate size while reapCount < maxQueueSize-1: print("Reader Process:%s"%messageQueue.get()) reapCount = reapCount + 1
if __name__ == "__main__": # Determine data size maxQueueSize = 10
multiprocessing.set_start_method = "fork"
messageQueue = multiprocessing.Queue()
writerProcess = multiprocessing.Process(target=writerProc, args=(messageQueue, maxQueueSize,)) readerProcess = multiprocessing.Process(target=readerProc, args=(messageQueue, maxQueueSize,))
writerProcess.start() readerProcess.start()
writerProcess.join() readerProcess.join() |
Output:
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Reader Process:Message1 Reader Process:Message2 Reader Process:Message3 Reader Process:Message4 Reader Process:Message5 Reader Process:Message6 Reader Process:Message7 Reader Process:Message8 Reader Process:Message9 |