python为什么此子流程命令无法按预期工作

Question

I was trying to use subprocess to extract lines from log file. The intention here is to extract the logs while some program is getting executed and wait for some time copy all the logs to another file.

#!/bin/python

import threading
import time, subprocess


class GetLogs(threading.Thread):
    '''
      Get the developer logs
    '''
    def __init__(self):
        '''
         init
        '''
        self.stop = False
        threading.Thread.__init__(self)
        print "Initialised thread"

    def run(self):
        '''
          Collect the logs from devlog
        '''
        command = "tail -f /var/log/developer_log | tee /tmp/log_collected"
        response = subprocess.check_output(command.split(), shell=True)
        print "Subprocess called"+str(response)

        while ( self.stop is False ):
            time.sleep(1)
            print "Continuing"
            continue

        print "Finished the log file"


gl = GetLogs()
gl.start()

##Do some activity here
print "Sleeping for 10 sec"
time.sleep(10)
gl.strop = True

print "Done"

This doesn't work - program gets stuck.

Answer 1

subprocess.check_output() waits for all the output. It waits for the child process to exit or close its STDOUT stream.

tail -f never exits and never closes its STDOUT stream. Therefore none of the lines of code below the call to check_output() will execute.

As the warning about deadlocks in https://docs.python.org/2/library/subprocess.html suggests, look at using Popen() and communicate() instead.