Python线程化多个bash子进程？

Question

如何使用线程和子进程模块来生成并行 bash 进程？当我在这里启动线程时，第一个答案是：How to use threading in Python?，bash 进程按顺序运行而不是并行运行。

Answer 1

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。一旦掌握了线程基础知识，那些更高级的技术似乎就不会太复杂。一旦掌握了这些技术，多处理就会变得更容易。

Answer 2

您不需要线程来并行运行子进程：

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()

---

要限制并发命令的数量，您可以使用使用线程并提供与使用进程的multiprocessing.Pool 相同的接口的multiprocessing.dummy.Pool：

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))

This answer demonstrates various techniques to limit number of concurrent subprocesses：它展示了基于 multiprocessing.Pool、concurrent.futures、threading + Queue 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，您可以避免忙循环和block on os.waitpid(-1, 0), to wait for any child process to exit。