Python 并发

• 

  简述

  并发经常被误解为并行。并发意味着调度独立的代码以系统的方式执行。本章重点介绍使用 Python 为操作系统执行并发。

  以下程序有助于执行操作系统的并发性 -

  
  import os
  import time
  import threading
  import multiprocessing
  NUM_WORKERS = 4
  def only_sleep():
     print("PID: %s, Process Name: %s, Thread Name: %s" % (
        os.getpid(),
        multiprocessing.current_process().name,
        threading.current_thread().name)
     )
     time.sleep(1)
  def crunch_numbers():
     print("PID: %s, Process Name: %s, Thread Name: %s" % (
        os.getpid(),
        multiprocessing.current_process().name,
        threading.current_thread().name)
     )
     x = 0
     while x < 10000000:
        x += 1
  for _ in range(NUM_WORKERS):
     only_sleep()
  end_time = time.time()
  print("Serial time=", end_time - start_time)
  # Run tasks using threads
  start_time = time.time()
  threads = [threading.Thread(target=only_sleep) for _ in range(NUM_WORKERS)]
  [thread.start() for thread in threads]
  [thread.join() for thread in threads]
  end_time = time.time()
  print("Threads time=", end_time - start_time)
  # Run tasks using processes
  start_time = time.time()
  processes = [multiprocessing.Process(target=only_sleep()) for _ in range(NUM_WORKERS)]
  [process.start() for process in processes]
  [process.join() for process in processes]
  end_time = time.time()
  print("Parallel time=", end_time - start_time)
  

  输出

  上述程序生成以下输出 -

  

  解释

  “multiprocessing”是一个类似于线程模块的包。这个包支持本地和远程并发。由于这个模块，程序员可以在给定系统上使用多个进程。