Does Queue.get block main?

Question

I know that Queue.get() method in python is a blocking function. I need to know if I implemented this function inside the main, waiting for an object set by a thread, does this means that all the main will be blocked.

For instance, if the main contains functions for transmitter and receiver, will the two work together or not?

Answer 1

Yes -- if you call some_queue.get() within either the thread or the main function, the program will block there until some object as passed through the queue.

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However, it is possible to use queues so that they don't block, or so that they have a timeout of some kind:

import Queue

while True:
    try:
        data = some_queue.get(False)  
        # If `False`, the program is not blocked. `Queue.Empty` is thrown if 
        # the queue is empty
    except Queue.Empty:
        data = None

    try:
        data2 = some_queue.get(True, 3)  
        # Waits for 3 seconds, otherwise throws `Queue.Empty`
    except Queue.Empty:
        data = None

You can do the same for some_queue.put -- either do some_queue.put(item, False) for non-blocking queues, or some_queue.put(item, True, 3) for timeouts. If your queue has a size limit, it will throw a Queue.Full exception if there is no more room left to append a new item.