Python线程化多个bash子进程？

Question

如何使用线程和子流程模块生成并行bash流程？ 当我启动线程时，这里的第一个答案是： 如何在Python中使用线程？ ，bash进程按顺序运行，而不是并行运行。

Answer 1

您不需要线程来并行运行子流程：

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()

---

要限制并发命令的数量，你可以使用multiprocessing.dummy.Pool使用线程，并提供相同的接口multiprocessing.Pool使用流程：

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))

该答案演示了限制并发子进程数的各种技术 ：它显示了multiprocessing.Pool，concurrent.futures，线程+基于队列的解决方案。

---

您可以限制并发子进程的数量，而无需使用线程/进程池：

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，您可以避免繁忙的循环并在os.waitpid(-1, 0)上进行os.waitpid(-1, 0) ，以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，有更好的方法可以执行某些操作，但这并不太复杂。 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。 掌握了线程基础知识之后，那些更高级的技术似乎并不太复杂。 一旦掌握了这些技术，多处理将变得更加容易。

Answer 3

这是因为它应该执行，所以您要做的不是multithreadind，而是多处理，请参见此堆栈页面