python - Python线程化多个bash子进程？

Question

如何使用线程和子进程模块来产生并行 bash 进程？当我开始线程时，这里的第一个答案是：如何在 Python 中使用线程？，bash 进程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()

---

为了限制您可以使用的并发命令的数量，这些命令使用线程并提供与使用进程multiprocessing.dummy.Pool相同的接口：multiprocessing.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))

这个答案演示了限制并发子进程数量的各种技术：它显示了基于 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，您可以避免忙循环并阻塞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。