蟒子輪詢（）沒有返回無即使POPEN仍在運行

Question

我有使用while循環和睡眠像下面

fout = tempfile.TemporaryFile() 
try: 
    p = subprocess.Popen(["/bin/bash","-c", options.command], bufsize=-1, shell=False, preexec_fn=os.setsid, stdin=subprocess.PIPE, stdout=fout, stderr=subprocess.PIPE) 
except: 
    sys.exit(UNEXPECTED_ERROR) 
if options.timeout: 
    print "options.timeout = %s" % options.timeout 
    elapsed = 0 
    time.sleep(0.1) # This sleep is for the delay between Popen and poll() functions 
    while p.poll() is None: 
     time.sleep(1) 
     elapsed = elapsed + 1 
     print "elapsed = %s" % elapsed 
     if elapsed >= options.timeout: 
      # TIMEDOUT 
      # kill all processes that are in the same child process group 
      # which kills the process tree 
      pgid = os.getpgid(p.pid)  
      os.killpg(pgid, signal.SIGKILL) 
      p.wait() 
      fout.close() 
      sys.exit(TIMEOUT_ERROR) 
      break 
else: 
    p.wait() 

fout.seek(0) #rewind to the beginning of the file 
print fout.read(), 
fout.close() 
sys.exit(p.returncode) 

$ time myScript -c "cat file2" 2>&1 -t 5 
options.timeout = 5 
elapsed = 1 

real 0m11.811s 
user 0m0.046s 
sys  0m1.153s 

我的問題是在這上面超時執行的Linux命令的python腳本即使超時時間爲5秒，貓也會一直持續到完成。我在這裏錯過了什麼嗎？請幫忙。

Answer 1

它將按預期在Ubuntu：

$ /usr/bin/ssh root@localhost -t 'sync && echo 3 > /proc/sys/vm/drop_caches' 
$ /usr/bin/time python2.4 myscript.py 'cat big_file' 
timeout 
done 
0.01user 0.63system 0:05.16elapsed 12%CPU 

$ /usr/bin/ssh root@localhost -t 'sync && echo 3 > /proc/sys/vm/drop_caches' 
$ /usr/bin/time cat big_file >/dev/null 
0.02user 0.82system 0:09.93elapsed 8%CPU 

它也可以用shell命令工作：

$ /usr/bin/time python2.4 myscript.py 'while : ; do sleep 1; done' 
timeout 
done 
0.02user 0.00system 0:05.03elapsed 0%CPU 

假設：

• 不能使用time.time()因系統時鐘變化的可能性

• time.clock()沒有衡量孩子的時間在Linux上

• 我們不能在純Python 由於​​在Python 3.3模擬time.monotonic()不可用Python的2.4

• 是可以接受的生存冬眠例如，在休眠之前2秒+在計算機被喚醒後3秒，如果超時爲5秒，則每當它發生時喚醒。

#!/usr/bin/env python2.4 
import os 
import signal 
import sys 
import tempfile 
import time 
from subprocess import Popen 

class TimeoutExpired(Exception): 
    pass 

def wait(process, timeout, _sleep_time=.1): 
    for _ in xrange(int(timeout * 1./_sleep_time + .5)): 
     time.sleep(_sleep_time) # NOTE: assume it doesn't wake up earlier 
     if process.poll() is not None: 
      return process.wait() 
    raise TimeoutExpired # NOTE: timeout precision is not very good 

f = tempfile.TemporaryFile() 
p = Popen(["/bin/bash", "-c", sys.argv[1]], stdout=f, preexec_fn=os.setsid, 
      close_fds=True) 
try: 
    wait(p, timeout=5) 
except TimeoutExpired: 
    print >>sys.stderr, "timeout" 
    os.killpg(os.getpgid(p.pid), signal.SIGKILL) 
    p.wait() 
else: 
    f.seek(0) 
    for line in f: 
     print line, 
f.close() # delete it 
print >>sys.stderr, "done" 

Answer 2

除了在你的代碼

• 我看到的問題你叫Popen()與stdin=subprocess.PIPE和stderr=subprocess.PIPE。但你永遠不會處理這些管道。使用像cat file2這樣的命令，這應該很好，但它可能會導致問題。

我可以發現一個潛在的不當行爲：你可能混淆了縮進（如在你的問題的第一個版本中）。假設你有以下幾點：

while p.poll() is None: 
    time.sleep(1) 
    elapsed = elapsed + 1 
    print "elapsed = %s" % elapsed 
    if elapsed >= options.timeout: 
     # TIMEDOUT 
     # kill all processes that are in the same child process group 
     # which kills the process tree 
     pgid = os.getpgid(p.pid)  
     os.killpg(pgid, signal.SIGKILL) 
    p.wait() 
    fout.close() 
    sys.exit(TIMEOUT_ERROR) 
    break 

你沒有達到超時臨界值，並且仍然p.wait()被稱爲由於壞的壓痕。不要混合標籤和空格; PEP 8建議只使用空格和4列的縮進深度。