Usage of queue (queue) module under Python thread (with examples)

The content of this article is about the usage of the queue (queue) module under Python threads. It has certain reference value. Friends in need can refer to it. I hope it will be helpful to you.

The queue module implements various [multi-producer-multi-consumer] queues. Can be used to safely exchange information between multiple threads of execution.

The queue module defines 3 different queue classes.

3 different queue classes

q=Queue(maxsize): Create a FIFO (first-in first-out, first-in first-out) queue. maxsize is the maximum number of items to put in the queue.
If the maxsize parameter is omitted or set to 0, the queue size will be infinite.

q=LifoQueue(maxsize): Create a LIFO (last-in first-out, last-in-first-out) queue (stack).

q=PriorityQueue(maxsize): Create a priority queue in which items are arranged in order from low to high priority.
When using this kind of queue, the item should be a tuple in the form of (priority, data), where priority is a number identifying the priority.

Common methods

q.size(): Returns the correct size of the queue. Because other threads may be updating this queue, the number returned by this method is unreliable.

q.empty(): If the queue is empty, return True, otherwise return False.

q.full(): If the queue is full, return True, otherwise return False.

q.put(item,block,timeout): Put the item into the queue.
If block is set to True (default value), the caller will be blocked until an available free position appears in the queue.
If block is set to False, this method will throw a Full exception when the queue is full.

q.put_nowait(item): Equivalent to q.put(item,False)

q.get(block, timeout): Delete an item from the queue and return the item .
If block is set to True (default value), the caller will block until available idle time appears in the queue.
If block is set to False, an Empty exception will be thrown when the queue is empty.
timeout provides an optional timeout value in seconds. If it times out, an Empty exception will be thrown.

q.get_nowait(): Equivalent to get(0)

q.task_done(): Used by consumers of data in the queue to indicate that processing of the item has ended. If you use this method, it should be called once for each item removed from the queue.

q.join(): Blocks until all items in the queue have been removed and processed. This method will return directly once the q.task_done() method has been called once for each item in the queue.

Example:

Using queues can generally simplify multi-threaded programs. For example, you can use shared queues to connect threads together without having to rely on locks for protection.

In this model, the worker thread generally acts as a consumer of data.

from threading import Thread
from queue import Queue
class WorkerThread(Thread):
    def __init__(self,*args,**kwargs):
        Thread.__init__(self,*args,**kwargs)
        self.input_queue=Queue()

    def send(self,item):
        self.input_queue.put(item)
    def close(self):
        self.input_queue.put(None)
        self.input_queue.join()
    def run(self):
        while True:
            item=self.input_queue.get()
            if item is None:
                break
            #实际开发中，此处应该使用有用的工作代替
            print(item)
            self.input_queue.task_done()
        #完成，指示收到和返回哨兵
        self.input_queue.task_done()
        return

if __name__=="__main__":
    w=WorkerThread()
    w.start()
    w.send("php")
    w.send("中")
    w.send("文")
    w.send("网")
    w.close()

Run results:

php
中
文
网

Related recommendations:

Comprehensive analysis of the python thread priority queue (queue) principle

How to use Queue and Condition for thread synchronization in Python

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