import time, os, select, signal
class subProcess:
"""Class representing a child process. It's like popen2.Popen3
but there are three main differences.
1. This makes the new child process group leader (using setpgrp())
so that all children can be killed.
2. The output function (read) is optionally non blocking returning in
specified timeout if nothing is read, or as close to specified
timeout as possible if data is read.
3. The output from both stdout & stderr is read (into outdata and
errdata). Reading from multiple outputs while not deadlocking
is not trivial and is often done in a non robust manner."""
def __init__(self, cmd, bufsize=8192):
"""The parameter 'cmd' is the shell command to execute in a
sub-process. If the 'bufsize' parameter is specified, it
specifies the size of the I/O buffers from the child process."""
self.cleaned=False
self.BUFSIZ=bufsize
self.outr, self.outw = os.pipe()
self.errr, self.errw = os.pipe()
self.pid = os.fork()
if self.pid == 0:
self._child(cmd)
os.close(self.outw) #parent doesn't write so close
os.close(self.errw)
# Note we could use self.stdout=fdopen(self.outr) here
# to get a higher level file object like popen2.Popen3 uses.
# This would have the advantages of auto handling the BUFSIZ
# and closing the files when deleted. However it would mean
# that it would block waiting for a full BUFSIZ unless we explicitly
# set the files non blocking, and there would be extra uneeded
# overhead like EOL conversion. So I think it's handier to use os.read()
self.outdata = self.errdata = ''
self._outeof = self._erreof = 0
def _child(self, cmd):
# Note sh below doesn't setup a seperate group (job control)
# for non interactive shells (hmm maybe -m option does?)
os.setpgrp() #seperate group so we can kill it
os.dup2(self.outw,1) #stdout to write side of pipe
os.dup2(self.errw,2) #stderr to write side of pipe
#stdout & stderr connected to pipe, so close all other files
map(os.close,[self.outr,self.outw,self.errr,self.errw])
try:
cmd = ['/bin/sh', '-c', cmd]
os.execvp(cmd[0], cmd)
finally: #exit child on error
os._exit(1)
def read(self, timeout=None):
"""return 0 when finished
else return 1 every timeout seconds
data will be in outdata and errdata"""
currtime=time.time()
while 1:
tocheck=[]
if not self._outeof:
tocheck.append(self.outr)
if not self._erreof:
tocheck.append(self.errr)
ready = select.select(tocheck,[],[],timeout)
if len(ready[0]) == 0: #no data timeout
return 1
else:
if self.outr in ready[0]:
outchunk = os.read(self.outr,self.BUFSIZ)
if outchunk == '':
self._outeof = 1
self.outdata += outchunk
if self.errr in ready[0]:
errchunk = os.read(self.errr,self.BUFSIZ)
if errchunk == '':
self._erreof = 1
self.errdata += errchunk
if self._outeof and self._erreof:
return 0
elif timeout:
if (time.time()-currtime) > timeout:
return 1 #may be more data but time to go
def kill(self):
os.kill(-self.pid, signal.SIGTERM) #kill whole group
def cleanup(self):
"""Wait for and return the exit status of the child process."""
self.cleaned=True
os.close(self.outr)
os.close(self.errr)
pid, sts = os.waitpid(self.pid, 0)
if pid == self.pid:
self.sts = sts
return self.sts
def __del__(self):
if not self.cleaned:
self.cleanup()
