Python:在p中执行cat子进程

Question

我正在远程服务器上运行几个cat | zgrep命令，并分别收集它们的输出以进行进一步处理：

class MainProcessor(mp.Process):
    def __init__(self, peaks_array):
        super(MainProcessor, self).__init__()
        self.peaks_array = peaks_array

    def run(self):
        for peak_arr in self.peaks_array:
            peak_processor = PeakProcessor(peak_arr)
            peak_processor.start()

class PeakProcessor(mp.Process):
    def __init__(self, peak_arr):
        super(PeakProcessor, self).__init__()
        self.peak_arr = peak_arr

    def run(self):
        command = 'ssh remote_host cat files_to_process | zgrep --mmap "regex" '
        log_lines = (subprocess.check_output(command, shell=True)).split('\n')
        process_data(log_lines)

但是，这会导致子进程的顺序执行（'ssh。。。猫…’）命令。第二个高峰等待第一个高峰结束，以此类推。

如何修改此代码以使子流程调用并行运行，同时仍然能够单独收集每个调用的输出？

Answer 1

不需要multiprocessing或threading来并行运行子进程，例如：

#!/usr/bin/env python
from subprocess import Popen

# run commands in parallel
processes = [Popen("echo {i:d}; sleep 2; echo {i:d}".format(i=i), shell=True)
             for i in range(5)]
# collect statuses
exitcodes = [p.wait() for p in processes]

它同时运行5个shell命令。注意：这里既不使用线程也不使用multiprocessing模块。没有必要在shell命令中添加与号和&：Popen不会等待命令完成。您需要显式调用.wait()。

这很方便，但不必使用线程从子进程收集输出：

#!/usr/bin/env python
from multiprocessing.dummy import Pool # thread pool
from subprocess import Popen, PIPE, STDOUT

# run commands in parallel
processes = [Popen("echo {i:d}; sleep 2; echo {i:d}".format(i=i), shell=True,
                   stdin=PIPE, stdout=PIPE, stderr=STDOUT, close_fds=True)
             for i in range(5)]

# collect output in parallel
def get_lines(process):
    return process.communicate()[0].splitlines()

outputs = Pool(len(processes)).map(get_lines, processes)

相关：Python threading multiple bash subprocesses?。

下面是在同一线程中同时从多个子进程获取输出的代码示例：

#!/usr/bin/env python3
import asyncio
import sys
from asyncio.subprocess import PIPE, STDOUT

@asyncio.coroutine
def get_lines(shell_command):
    p = yield from asyncio.create_subprocess_shell(shell_command,
            stdin=PIPE, stdout=PIPE, stderr=STDOUT)
    return (yield from p.communicate())[0].splitlines()

if sys.platform.startswith('win'):
    loop = asyncio.ProactorEventLoop() # for subprocess' pipes on Windows
    asyncio.set_event_loop(loop)
else:
    loop = asyncio.get_event_loop()

# get commands output in parallel
coros = [get_lines('"{e}" -c "print({i:d}); import time; time.sleep({i:d})"'
                    .format(i=i, e=sys.executable)) for i in range(5)]
print(loop.run_until_complete(asyncio.gather(*coros)))
loop.close()

Answer 2

另一种方法（而不是将shell进程放在后台的其他建议）是使用multithreading.

然后，您所拥有的run方法将执行如下操作：

thread.start_new_thread ( myFuncThatDoesZGrep)

要收集结果，可以执行以下操作：

class MyThread(threading.Thread):
   def run(self):
       self.finished = False
       # Your code to run the command here.
       blahBlah()
       # When finished....
       self.finished = True
       self.results = []

在多线程链接中运行上述线程。当线程对象的myThread.finished==True时，可以通过myThread.results收集结果。