Two functions: one which waits for a certain PID to terminate (with optional timeout), another one which checks whether a process with a given PID is running.
This was extracted from psutil project which also provides a Windows implementation.
Timeout functionality is implemented as a busy loop and it was inspired by http://bugs.python.org/issue5673.
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"""
Wait for a certain PID to terminate and check for PID existance (POSIX).
"""
# Author: Giampaolo Rodola' <g.rodola [AT] gmail [DOT] com>
# License: MIT
import os
import time
import errno
class TimeoutExpired(Exception):
pass
def pid_exists(pid):
"""Check whether pid exists in the current process table."""
if pid < 0:
return False
try:
os.kill(pid, 0)
except OSError, e:
return e.errno == errno.EPERM
else:
return True
def wait_pid(pid, timeout=None):
"""Wait for process with pid 'pid' to terminate and return its
exit status code as an integer.
If pid is not a children of os.getpid() (current process) just
waits until the process disappears and return None.
If pid does not exist at all return None immediately.
Raise TimeoutExpired on timeout expired (if specified).
"""
def check_timeout(delay):
if timeout is not None:
if time.time() >= stop_at:
raise TimeoutExpired
time.sleep(delay)
return min(delay * 2, 0.04)
if timeout is not None:
waitcall = lambda: os.waitpid(pid, os.WNOHANG)
stop_at = time.time() + timeout
else:
waitcall = lambda: os.waitpid(pid, 0)
delay = 0.0001
while 1:
try:
retpid, status = waitcall()
except OSError, err:
if err.errno == errno.EINTR:
delay = check_timeout(delay)
continue
elif err.errno == errno.ECHILD:
# This has two meanings:
# - pid is not a child of os.getpid() in which case
# we keep polling until it's gone
# - pid never existed in the first place
# In both cases we'll eventually return None as we
# can't determine its exit status code.
while 1:
if pid_exists(pid):
delay = check_timeout(delay)
else:
return
else:
raise
else:
if retpid == 0:
# WNOHANG was used, pid is still running
delay = check_timeout(delay)
continue
# process exited due to a signal; return the integer of
# that signal
if os.WIFSIGNALED(status):
return os.WTERMSIG(status)
# process exited using exit(2) system call; return the
# integer exit(2) system call has been called with
elif os.WIFEXITED(status):
return os.WEXITSTATUS(status)
else:
# should never happen
raise RuntimeError("unknown process exit status")
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