python如何控制進(jìn)程或者線程的個數(shù)

更新時間：2020年10月16日 11:17:24 作者：項(xiàng)昂之的

這篇文章主要介紹了python如何控制進(jìn)程或者線程的個數(shù)，幫助大家更好的理解和使用python，感興趣的朋友可以了解下

背景

日常開發(fā)中，難免遇到并發(fā)場景，而并發(fā)場景難免需要做流量控制，即需要對并發(fā)的進(jìn)程或者線程的總量進(jìn)行控制。今天簡單總結(jié)兩種常用的控制線程個數(shù)的方法。

方法一：進(jìn)程池/線程池

如下例demo所示，創(chuàng)建了一個大小是4的進(jìn)程池，然后創(chuàng)建5個進(jìn)程，并啟動

from multiprocessing import Pool
import os, time, random


def long_time_task(name):
  print('Run task %s (%s)...' % (name, os.getpid()))
  start = time.time()
  time.sleep(random.random() * 3)
  end = time.time()
  print('Task %s runs %0.2f seconds.' % (name, (end - start)))


if __name__ == '__main__':
  print('Parent process %s.' % os.getpid())
  p = Pool(4)
  for i in range(5):
    p.apply_async(long_time_task, args=(i,))
  print('Waiting for all subprocesses done...')
  p.close()
  p.join()
  print('All subprocesses done.')

運(yùn)行結(jié)果如下，可以看到第5個進(jìn)程會等池子里的進(jìn)程完成一個后才會被啟動

Run task 0 (32952)...
Run task 1 (32951)...
Run task 2 (32953)...
Run task 3 (32954)...
Task 2 runs 0.68 seconds.
Run task 4 (32953)...
Task 1 runs 1.41 seconds.
Task 0 runs 1.44 seconds.
Task 4 runs 2.15 seconds.
Task 3 runs 2.98 seconds.
All subprocesses done.

方法二：queue

queue 模塊即隊(duì)列，特別適合處理信息在多個線程間安全交換的多線程程序中。下面的demo展示了如何通過queue來限制線程的并發(fā)個數(shù)

import threading
import queue
import time
import random
import os

maxThreads = 4


class Store(threading.Thread):
  def __init__(self, q):
    threading.Thread.__init__(self)
    self.queue = q
    # self.store = store

  def run(self):
    try:
      print('Run task (%s)...' % (os.getpid()))
      start = time.time()
      time.sleep(random.random() * 3)
      end = time.time()
      t = threading.currentThread()
      # 線程ID
      print('Thread id : %d' % t.ident)
      print('Thread name : %s' % t.getName())
      print('Task runs %0.2f seconds.' % (end - start))
    except Exception as e:
      print(e)
    finally:
      self.queue.get()
      self.queue.task_done()


def main():
  q = queue.Queue(maxThreads)
  for s in range(6):
    q.put(s)
    t = Store(q)
    t.start()
  q.join()
  print('over')


if __name__ == '__main__':
  main()

運(yùn)行結(jié)果如下：

Run task (33259)...
Run task (33259)...
Run task (33259)...
Run task (33259)...
Thread id : 123145444999168
Thread name : Thread-13
Task runs 0.04 seconds.
Run task (33259)...
Thread id : 123145394630656
Thread name : Thread-10
Task runs 1.02 seconds.
Run task (33259)...
Thread id : 123145428209664
Thread name : Thread-12
Task runs 1.20 seconds.
Thread id : 123145394630656
Thread name : Thread-17
Task runs 0.68 seconds.
Thread id : 123145444999168
Thread name : Thread-14
Task runs 1.79 seconds.
Thread id : 123145411420160
Thread name : Thread-11
Task runs 2.96 seconds.
over

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