Python线程化多个bash子进程？

Question

如何使用线程和子进程模块生成并行bash进程？当我启动线程时,第一个答案就在这里:如何在Python中使用线程？,bash进程按顺序而不是并行运行.

Answer 1

您不需要线程并行运行子进程:

from subprocess import Popen

commands = [
    'date; ls -l; sleep 1; date',
    'date; sleep 5; date',
    'date; df -h; sleep 3; date',
    'date; hostname; sleep 2; date',
    'date; uname -a; date',
]
# run in parallel
processes = [Popen(cmd, shell=True) for cmd in commands]
# do other things here..
# wait for completion
for p in processes: p.wait()

要限制可以使用的并发命令数,multiprocessing.dummy.Pool它们使用线程并提供与multiprocessing.Pool使用进程相同的接口:

from functools import partial
from multiprocessing.dummy import Pool
from subprocess import call

pool = Pool(2) # two concurrent commands at a time
for i, returncode in enumerate(pool.imap(partial(call, shell=True), commands)):
    if returncode != 0:
       print("%d command failed: %d" % (i, returncode))

这个答案演示了限制并发子进程数的各种技术:它显示了多处理.Pool,concurrent.futures,threading +基于队列的解决方案.

您可以在不使用线程/进程池的情况下限制并发子进程的数量:

from subprocess import Popen
from itertools import islice

max_workers = 2  # no more than 2 concurrent processes
processes = (Popen(cmd, shell=True) for cmd in commands)
running_processes = list(islice(processes, max_workers))  # start new processes
while running_processes:
    for i, process in enumerate(running_processes):
        if process.poll() is not None:  # the process has finished
            running_processes[i] = next(processes, None)  # start new process
            if running_processes[i] is None: # no new processes
                del running_processes[i]
                break

在Unix上,你可以避免忙循环和阻塞os.waitpid(-1, 0),等待任何子进程退出.

Answer 2

一个简单的线程示例:

import threading
import Queue
import commands
import time

# thread class to run a command
class ExampleThread(threading.Thread):
    def __init__(self, cmd, queue):
        threading.Thread.__init__(self)
        self.cmd = cmd
        self.queue = queue

    def run(self):
        # execute the command, queue the result
        (status, output) = commands.getstatusoutput(self.cmd)
        self.queue.put((self.cmd, output, status))

# queue where results are placed
result_queue = Queue.Queue()

# define the commands to be run in parallel, run them
cmds = ['date; ls -l; sleep 1; date',
        'date; sleep 5; date',
        'date; df -h; sleep 3; date',
        'date; hostname; sleep 2; date',
        'date; uname -a; date',
       ]
for cmd in cmds:
    thread = ExampleThread(cmd, result_queue)
    thread.start()

# print results as we get them
while threading.active_count() > 1 or not result_queue.empty():
    while not result_queue.empty():
        (cmd, output, status) = result_queue.get()
        print('%s:' % cmd)
        print(output)
        print('='*60)
    time.sleep(1)

请注意,有更好的方法可以做到这一点,但这不是太复杂.该示例为每个命令使用一个线程.当您想要执行诸如使用有限数量的线程来处理未知数量的命令之类的事情时,复杂性开始蔓延.一旦掌握了线程基础知识,那些更高级的技术似乎并不太复杂.一旦掌握了这些技术,多处理就变得更容易了.