Python 子进程带超时和大输出（>64K）
我想要执行一个进程，并设置一个超时时间（以秒为单位），同时获取这个进程产生的输出。我希望在Windows、Linux和FreeBSD上都能做到这一点。
我尝试了三种不同的方法：
cmd - 没有设置超时，并使用subprocess.PIPE来捕获输出。
表现：按预期工作，但不支持超时，我需要超时功能...
cmd_to - 设置了超时，并使用subprocess.PIPE来捕获输出。
表现：当输出大于等于65536字节时，会阻塞子进程的执行。
cmd_totf - 设置了超时，并使用tempfile.NamedTemporaryfile来捕获输出。
表现：按预期工作，但会在磁盘上使用临时文件。
下面可以更仔细地查看这些实现。
从下面的输出可以看出，当使用subprocess.PIPE并且子进程的输出大于等于65536字节时，超时代码会阻塞子进程的执行。
子进程的文档说明，当调用process.wait()并使用subprocess.PIPE时，这是预期的行为，但在使用process.poll()时并没有给出警告，那么这里到底出了什么问题呢？
我在cmd_totf中有一个解决方案，它使用了tempfile模块，但缺点是它会把输出写入磁盘，这我真的很想避免。
所以我的问题是：
- 我在cmd_to中做错了什么？
- 有没有办法实现我想要的功能，而不使用临时文件，或者把输出保存在内存中。
生成大量输出的脚本（'exp_gen.py'）：
#!/usr/bin/env python
import sys
output = "b"*int(sys.argv[1])
print output
围绕subprocessing.Popen的三种不同实现（cmd、cmd_to、cmd_totf）：
#!/usr/bin/env python
import subprocess, time, tempfile
bufsize = -1
def cmd(cmdline, timeout=60):
"""
Execute cmdline.
Uses subprocessing and subprocess.PIPE.
"""
p = subprocess.Popen(
cmdline,
bufsize = bufsize,
shell = False,
stdin = subprocess.PIPE,
stdout = subprocess.PIPE,
stderr = subprocess.PIPE
)
out, err = p.communicate()
returncode = p.returncode
return (returncode, err, out)
def cmd_to(cmdline, timeout=60):
"""
Execute cmdline, limit execution time to 'timeout' seconds.
Uses subprocessing and subprocess.PIPE.
"""
p = subprocess.Popen(
cmdline,
bufsize = bufsize,
shell = False,
stdin = subprocess.PIPE,
stdout = subprocess.PIPE,
stderr = subprocess.PIPE
)
t_begin = time.time() # Monitor execution time
seconds_passed = 0
while p.poll() is None and seconds_passed < timeout:
seconds_passed = time.time() - t_begin
time.sleep(0.1)
#if seconds_passed > timeout:
#
# try:
# p.stdout.close() # If they are not closed the fds will hang around until
# p.stderr.close() # os.fdlimit is exceeded and cause a nasty exception
# p.terminate() # Important to close the fds prior to terminating the process!
# # NOTE: Are there any other "non-freed" resources?
# except:
# pass
#
# raise TimeoutInterrupt
out, err = p.communicate()
returncode = p.returncode
return (returncode, err, out)
def cmd_totf(cmdline, timeout=60):
"""
Execute cmdline, limit execution time to 'timeout' seconds.
Uses subprocessing and tempfile instead of subprocessing.PIPE.
"""
output = tempfile.NamedTemporaryFile(delete=False)
error = tempfile.NamedTemporaryFile(delete=False)
p = subprocess.Popen(
cmdline,
bufsize = 0,
shell = False,
stdin = None,
stdout = output,
stderr = error
)
t_begin = time.time() # Monitor execution time
seconds_passed = 0
while p.poll() is None and seconds_passed < timeout:
seconds_passed = time.time() - t_begin
time.sleep(0.1)
#if seconds_passed > timeout:
#
# try:
# p.stdout.close() # If they are not closed the fds will hang around until
# p.stderr.close() # os.fdlimit is exceeded and cause a nasty exception
# p.terminate() # Important to close the fds prior to terminating the process!
# # NOTE: Are there any other "non-freed" resources?
# except:
# pass
#
# raise TimeoutInterrupt
p.wait()
returncode = p.returncode
fd = open(output.name)
out = fd.read()
fd.close()
fd = open(error.name)
err = fd.read()
fd.close()
error.close()
output.close()
return (returncode, err, out)
if __name__ == "__main__":
implementations = [cmd, cmd_to, cmd_totf]
bytes = ['65535', '65536', str(1024*1024)]
timeouts = [5]
for timeout in timeouts:
for size in bytes:
for i in implementations:
t_begin = time.time()
seconds_passed = 0
rc, err, output = i(['exp_gen.py', size], timeout)
seconds_passed = time.time() - t_begin
filler = ' '*(8-len(i.func_name))
print "[%s%s: timeout=%d, iosize=%s, seconds=%f]" % (repr(i.func_name), filler, timeout, size, seconds_passed)
执行的输出：
['cmd' : timeout=5, iosize=65535, seconds=0.016447]
['cmd_to' : timeout=5, iosize=65535, seconds=0.103022]
['cmd_totf': timeout=5, iosize=65535, seconds=0.107176]
['cmd' : timeout=5, iosize=65536, seconds=0.028105]
['cmd_to' : timeout=5, iosize=65536, seconds=5.116658]
['cmd_totf': timeout=5, iosize=65536, seconds=0.104905]
['cmd' : timeout=5, iosize=1048576, seconds=0.025964]
['cmd_to' : timeout=5, iosize=1048576, seconds=5.128062]
['cmd_totf': timeout=5, iosize=1048576, seconds=0.103183]
2 个回答
2
免责声明：这个答案没有在Windows或FreeBSD上测试过。不过使用的模块应该在这些系统上也能工作。我相信这应该是一个能解决你问题的有效答案——对我来说是有效的。
这是我在Linux上为了解决问题而编写的代码。它结合了几个Stackoverflow的讨论和我自己在Python 3文档中的研究。
这段代码的主要特点：
- 使用进程而不是线程来处理阻塞的输入输出，因为进程能更可靠地被终止。
- 实现了一个可重启的超时监控器，每当有输出时就重新开始计时。
- 实现了一个长期的超时监控器，以限制整体运行时间。
- 可以接收标准输入（虽然我只需要一次性输入短字符串）。
- 可以像往常一样捕获标准输出和标准错误输出（目前只编写了标准输出，标准错误输出被重定向到标准输出，但可以很容易分开）。
- 几乎是实时的，因为它每0.2秒检查一次输出。不过你可以轻松减少这个时间间隔或去掉等待时间。
- 还有很多调试信息输出，可以看到发生了什么事情。
唯一的代码依赖是enum，具体实现可以参考这里，不过代码可以很容易修改成不需要这个的样子。它只是用来区分两个超时——如果你愿意，可以使用不同的异常。
下面是代码——像往常一样，欢迎反馈：
(编辑于2012年6月29日——代码现在实际上可以工作)
# Python module runcmd
# Implements a class to launch shell commands which
# are killed after a timeout. Timeouts can be reset
# after each line of output
#
# Use inside other script with:
#
# import runcmd
# (return_code, out) = runcmd.RunCmd(['ls', '-l', '/etc'],
# timeout_runtime,
# timeout_no_output,
# stdin_string).go()
#
import multiprocessing
import queue
import subprocess
import time
import enum
def timestamp():
return time.strftime('%Y%m%d-%H%M%S')
class ErrorRunCmd(Exception): pass
class ErrorRunCmdTimeOut(ErrorRunCmd): pass
class Enqueue_output(multiprocessing.Process):
def __init__(self, out, queue):
multiprocessing.Process.__init__(self)
self.out = out
self.queue = queue
self.daemon = True
def run(self):
try:
for line in iter(self.out.readline, b''):
#print('worker read:', line)
self.queue.put(line)
except ValueError: pass # Readline of closed file
self.out.close()
class Enqueue_input(multiprocessing.Process):
def __init__(self, inp, iterable):
multiprocessing.Process.__init__(self)
self.inp = inp
self.iterable = iterable
self.daemon = True
def run(self):
#print("writing stdin")
for line in self.iterable:
self.inp.write(bytes(line,'utf-8'))
self.inp.close()
#print("writing stdin DONE")
class RunCmd():
"""RunCmd - class to launch shell commands
Captures and returns stdout. Kills child after a given
amount (timeout_runtime) wallclock seconds. Can also
kill after timeout_retriggerable wallclock seconds.
This second timer is reset whenever the child does some
output
(return_code, out) = RunCmd(['ls', '-l', '/etc'],
timeout_runtime,
timeout_no_output,
stdin_string).go()
"""
Timeout = enum.Enum('No','Retriggerable','Runtime')
def __init__(self, cmd, timeout_runtime, timeout_retriggerable, stdin=None):
self.dbg = False
self.cmd = cmd
self.timeout_retriggerable = timeout_retriggerable
self.timeout_runtime = timeout_runtime
self.timeout_hit = self.Timeout.No
self.stdout = '--Cmd did not yield any output--'
self.stdin = stdin
def read_queue(self, q):
time_last_output = None
try:
bstr = q.get(False) # non-blocking
if self.dbg: print('{} chars read'.format(len(bstr)))
time_last_output = time.time()
self.stdout += bstr
except queue.Empty:
#print('queue empty')
pass
return time_last_output
def go(self):
if self.stdin:
pstdin = subprocess.PIPE
else:
pstdin = None
p = subprocess.Popen(self.cmd, shell=False, stdout=subprocess.PIPE, stderr=subprocess.STDOUT, stdin=pstdin)
pin = None
if (pstdin):
pin = Enqueue_input(p.stdin, [self.stdin + '\n'])
pin.start()
q = multiprocessing.Queue()
pout = Enqueue_output(p.stdout, q)
pout.start()
try:
if self.dbg: print('Beginning subprocess with timeout {}/{} s on {}'.format(self.timeout_retriggerable, self.timeout_runtime, time.asctime()))
time_begin = time.time()
time_last_output = time_begin
seconds_passed = 0
self.stdout = b''
once = True # ensure loop's executed at least once
# some child cmds may exit very fast, but still produce output
while once or p.poll() is None or not q.empty():
once = False
if self.dbg: print('a) {} of {}/{} secs passed and overall {} chars read'.format(seconds_passed, self.timeout_retriggerable, self.timeout_runtime, len(self.stdout)))
tlo = self.read_queue(q)
if tlo:
time_last_output = tlo
now = time.time()
if now - time_last_output >= self.timeout_retriggerable:
self.timeout_hit = self.Timeout.Retriggerable
raise ErrorRunCmdTimeOut(self)
if now - time_begin >= self.timeout_runtime:
self.timeout_hit = self.Timeout.Runtime
raise ErrorRunCmdTimeOut(self)
if q.empty():
time.sleep(0.1)
# Final try to get "last-millisecond" output
self.read_queue(q)
finally:
self._close(p, [pout, pin])
return (self.returncode, self.stdout)
def _close(self, p, procs):
if self.dbg:
if self.timeout_hit != self.Timeout.No:
print('{} A TIMEOUT occured: {}'.format(timestamp(), self.timeout_hit))
else:
print('{} No timeout occured'.format(timestamp()))
for process in [proc for proc in procs if proc]:
try:
process.terminate()
except:
print('{} Process termination raised trouble'.format(timestamp()))
raise
try:
p.stdin.close()
except: pass
if self.dbg: print('{} _closed stdin'.format(timestamp()))
try:
p.stdout.close() # If they are not closed the fds will hang around until
except: pass
if self.dbg: print('{} _closed stdout'.format(timestamp()))
#p.stderr.close() # os.fdlimit is exceeded and cause a nasty exception
try:
p.terminate() # Important to close the fds prior to terminating the process!
# NOTE: Are there any other "non-freed" resources?
except: pass
if self.dbg: print('{} _closed Popen'.format(timestamp()))
try:
self.stdout = self.stdout.decode('utf-8')
except: pass
self.returncode = p.returncode
if self.dbg: print('{} _closed all'.format(timestamp()))
使用方法：
import runcmd
cmd = ['ls', '-l', '/etc']
worker = runcmd.RunCmd(cmd,
40, # limit runtime [wallclock seconds]
2, # limit runtime after last output [wallclk secs]
'' # stdin input string
)
(return_code, out) = worker.go()
if worker.timeout_hit != worker.Timeout.No:
print('A TIMEOUT occured: {}'.format(worker.timeout_hit))
else:
print('No timeout occured')
print("Running '{:s}' returned {:d} and {:d} chars of output".format(cmd, return_code, len(out)))
print('Output:')
print(out)
command - 第一个参数 - 应该是一个包含命令及其参数的列表。它用于Popen(shell=False)调用，超时以秒为单位。目前没有代码可以禁用超时。将timeout_no_output设置为time_runtime可以有效禁用可重启的timeout_no_output。
stdin_string可以是任何要发送到命令标准输入的字符串。如果你的命令不需要输入，可以设置为None。如果提供了字符串，最后会自动添加一个'\n'。
5
与子进程文档中的所有警告相反，直接从process.stdout和process.stderr读取数据提供了一个更好的解决方案。
这里说的更好是指，我可以读取一个进程的输出，超过2^16字节，而不需要暂时把这些输出存储到磁盘上。
下面是代码：
import fcntl
import os
import subprocess
import time
def nonBlockRead(output):
fd = output.fileno()
fl = fcntl.fcntl(fd, fcntl.F_GETFL)
fcntl.fcntl(fd, fcntl.F_SETFL, fl | os.O_NONBLOCK)
try:
return output.read()
except:
return ''
def cmd(cmdline, timeout=60):
"""
Execute cmdline, limit execution time to 'timeout' seconds.
Uses the subprocess module and subprocess.PIPE.
Raises TimeoutInterrupt
"""
p = subprocess.Popen(
cmdline,
bufsize = bufsize, # default value of 0 (unbuffered) is best
shell = False, # not really needed; it's disabled by default
stdout = subprocess.PIPE,
stderr = subprocess.PIPE
)
t_begin = time.time() # Monitor execution time
seconds_passed = 0
stdout = ''
stderr = ''
while p.poll() is None and seconds_passed < timeout: # Monitor process
time.sleep(0.1) # Wait a little
seconds_passed = time.time() - t_begin
# p.std* blocks on read(), which messes up the timeout timer.
# To fix this, we use a nonblocking read()
# Note: Not sure if this is Windows compatible
stdout += nonBlockRead(p.stdout)
stderr += nonBlockRead(p.stderr)
if seconds_passed >= timeout:
try:
p.stdout.close() # If they are not closed the fds will hang around until
p.stderr.close() # os.fdlimit is exceeded and cause a nasty exception
p.terminate() # Important to close the fds prior to terminating the process!
# NOTE: Are there any other "non-freed" resources?
except:
pass
raise TimeoutInterrupt
returncode = p.returncode
return (returncode, stdout, stderr)