python - subprocess.popen() stderr 重定向与管道/失败

Question

我想运行一个进程，该进程可能会在超时秒内产生大量输出，捕获 stdout/stderr。根据 documentation for subprocess，使用 capture() 和 PIPE 作为 stdout/stderr 容易出现死锁.

现在，无论如何我都在使用 poll() —— 因为我希望能够在超时后终止进程 —— 但我仍然不知道如何避免死锁使用管道。我该怎么做？

目前我只是通过创建临时文件来解决问题:

#because of the shitty api, this has to be a file, because std.PIPE is prone to deadlocking with a lot of output, and I can't figure out what to do about it
out, outfile = tempfile.mkstemp()
err, errfile = tempfile.mkstemp()

now = datetime.datetime.now().strftime('%H:%M, %Ss')
print "Running '" + exe + "' with a timeout of ", timeout , "s., starting at ", now
p = subprocess.Popen(args = exe,
                     stdout = out,
                     #for some reason, err isn't working if the process is killed by the kernel for, say, using too much memory.
                     stderr = err,
                     cwd = dir)

start = time.time()

# take care of infinite loops
sleepDuration = 0.25
time.sleep(0.1)
lastPrintedDuration = 0
duration = 0
while p.poll() is None:
    duration = time.time() - start
    if duration > lastPrintedDuration + 1:
        lastPrintedDuration += 1
        #print '.',
        sys.stdout.flush()
    if duration >= timeout:
        p.kill()
        raise Exception("Killed after " + str(duration) + "s.")
    time.sleep(sleepDuration)

if p.returncode is not 0:
    with open(errfile, 'r') as f:
        e = f.read()
        #fix empty error messages
        if e == '':
            e = 'Program crashed, or was killed by kernel.'
        f.close()

    os.close(out)
    os.close(err)
    os.unlink(outfile)
    os.unlink(errfile)
    print "Error after " + str(duration) + 's: ',
    print "'" + e + "'"
    raw_input('test')
    raise Exception(e)
else:
    print "completed in " + str(duration) + 's.'

os.close(out)
os.close(err)
os.unlink(outfile)
os.unlink(errfile)

但如果进程被内核杀死(内存不足等)，即使这样也无法捕获错误。

这个问题的理想解决方案是什么？

Answer 1

不使用文件作为输出，返回使用管道，而是使用 fcntl模块将 p.stdout 和 p.stderr 置于非阻塞模式。这将导致 p.stdout.read() 和 p.stderr.read() 返回任何可用数据或引发 IOError 如果没有数据，而不是阻塞:

import fcntl, os

p = subprocess.Popen(args = exe,
                     stdout = subprocess.PIPE,
                     stderr = subprocess.PIPE,
                     cwd = dir)
fcntl.fcntl(p.stdout.fileno(), fcntl.F_SETFL, os.O_NONBLOCK)
fcntl.fcntl(p.stderr.fileno(), fcntl.F_SETFL, os.O_NONBLOCK)

outdata, errdata = '', ''
while p.poll() is None:
    try:
        outdata += p.stdout.read()
    except IOError:
        pass
    try:
        errdata += p.stderr.read()
    except IOError:
        pass
    time.sleep(sleepDuration)

正如 glglgl 在评论中指出的，您应该在 except IOError 子句中做一些额外的检查，以确保它实际上不是真正的错误。