python–subprocess.popen()使用管道/失败的stderr重定向

我想运行一个进程,它可以产生大量输出,最多超时秒,捕获stdout / stderr.根据documentation for subprocess,使用capture()和PIPE作为stdout / stderr很容易发生死锁.

现在,我正在使用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使用PIPE来避免死锁.我怎么做？

目前我只是通过创建临时文件来解决：

#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)


但是,如果进程被内核(内存不足等)杀死,即使这样也无法捕获错误.

什么是这个问题的理想解决方案？

解决方法:

不使用文件作为输出,而是返回使用管道,但使用fcntl模块将p.stdout和p.stder变为非阻塞模式.这将导致p.stdout.read()和p.stderr.read()返回任何可用数据,或者如果没有数据则引发IOError,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在注释中指出的那样,你应该在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.