3

最近在队列设计中介绍了延迟处理以及实现“FIFO”等的能力。

浏览了文档，试图获得一个示例队列，以了解如何在我自己的设计/程序中实现它。但是我在运行这段代码时遇到了问题：

import queue

def worker():
    while True:
        item = q.get()
        do_work(item)
        q.task_done()

def main():

    q = queue.Queue(maxsize=0)
    for i in range(num_worker_threads):
         t = Thread(target=worker)
         t.daemon = True
         t.start()

    for item in source():
        q.put(item)

    q.join()       # block until all tasks are done

main()

问题：希望有人解释 for 循环在做什么，我在运行代码时遇到错误，所以我必须遗漏一些东西。

发生的问题错误： NameError：未定义全局名称'num_worker_threads'

谢谢你来自-Python新手-

4

2 回答 2

23

for 循环正在启动许多工作线程来执行“worker”定义的功能。这是应该在您的系统上以 python 2.7 运行的工作代码。

import Queue
import threading

# input queue to be processed by many threads
q_in = Queue.Queue(maxsize=0)

# output queue to be processed by one thread
q_out = Queue.Queue(maxsize=0)

# number of worker threads to complete the processing
num_worker_threads = 10

# process that each worker thread will execute until the Queue is empty
def worker():
    while True:
        # get item from queue, do work on it, let queue know processing is done for one item
        item = q_in.get()
        q_out.put(do_work(item))
        q_in.task_done()

# squares a number and returns the number and its square
def do_work(item):
    return (item,item*item)

# another queued thread we will use to print output
def printer():
    while True:
        # get an item processed by worker threads and print the result. Let queue know item has been processed
        item = q_out.get()
        print "%d squared is : %d" % item
        q_out.task_done()

# launch all of our queued processes
def main():
    # Launches a number of worker threads to perform operations using the queue of inputs
    for i in range(num_worker_threads):
         t = threading.Thread(target=worker)
         t.daemon = True
         t.start()

    # launches a single "printer" thread to output the result (makes things neater)
    t = threading.Thread(target=printer)
    t.daemon = True
    t.start()

    # put items on the input queue (numbers to be squared)
    for item in range(10):
        q_in.put(item)

    # wait for two queues to be emptied (and workers to close)   
    q_in.join()       # block until all tasks are done
    q_out.join()

    print "Processing Complete"

main()

每个 @handle 的 Python 3 版本

import queue 
import threading

# input queue to be processed by many threads
q_in = queue.Queue(maxsize=0) 

# output queue to be processed by one thread
q_out = queue.Queue(maxsize=0) 

# number of worker threads to complete the processing
num_worker_threads = 10

# process that each worker thread will execute until the Queue is empty
def worker():
    while True:
        # get item from queue, do work on it, let queue know processing is done for one item
        item = q_in.get()
        q_out.put(do_work(item))
        q_in.task_done()

# squares a number and returns the number and its square
def do_work(item):
    return (item,item*item)

# another queued thread we will use to print output
def printer():
    while True:
        # get an item processed by worker threads and print the result. Let queue know item has been processed
        item = q_out.get()
        print("{0[0]} squared is : {0[1]}".format(item) )
        q_out.task_done()

# launch all of our queued processes
def main():
    # Launches a number of worker threads to perform operations using the queue of inputs
    for i in range(num_worker_threads):
         t = threading.Thread(target=worker)
         t.daemon = True
         t.start()

    # launches a single "printer" thread to output the result (makes things neater)
    t = threading.Thread(target=printer)
    t.daemon = True
    t.start()

    # put items on the input queue (numbers to be squared)
    for item in range(10):
        q_in.put(item)

    # wait for two queues to be emptied (and workers to close)   
    q_in.join()       # block until all tasks are done
    q_out.join()

    print( "Processing Complete" )

main()
于 2013-01-29T15:41:48.390 回答
3

您可以将工作线程的数量视为银行的银行柜员数量。因此，人们（您的物品）排队（您的队列）由银行出纳员（您的工作线程）处理。队列实际上是一种简单且易于理解的机制来管理线程中的复杂性。

我已经稍微调整了您的代码以显示它是如何工作的。

import queue
import time
from threading import Thread

def do_work(item):
    print("processing", item)

def source():
    item = 1
    while True:
        print("starting", item)
        yield item
        time.sleep(0.2)
        item += 1

def worker():
    while True:
        item = q.get()
        do_work(item)
        q.task_done()

q = queue.Queue(maxsize=0)
def main():
    for i in range(2):
        t = Thread(target=worker)
        t.daemon = True
        t.start()

    for item in source():
        q.put(item)

    q.join()       # block until all tasks are done

main()
于 2013-01-29T15:31:23.683 回答