mailinabox/management/utils.py

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Python
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2014-06-03 20:21:17 +00:00
def load_environment():
# Load settings from /etc/mailinabox.conf.
import os.path
env = { }
for line in open("/etc/mailinabox.conf"): env.setdefault(*line.strip().split("=", 1))
env["CONF_DIR"] = os.path.join(os.path.dirname(__file__), "../conf")
return env
def exclusive_process(name):
# Ensure that a process named `name` does not execute multiple
# times concurrently.
import os, sys, atexit
pidfile = '/var/run/mailinabox-%s.pid' % name
mypid = os.getpid()
# Attempt to get a lock on ourself so that the concurrency check
# itself is not executed in parallel.
with open(__file__, 'r+') as flock:
# Try to get a lock. This blocks until a lock is acquired. The
# lock is held until the flock file is closed at the end of the
# with block.
os.lockf(flock.fileno(), os.F_LOCK, 0)
# While we have a lock, look at the pid file. First attempt
# to write our pid to a pidfile if no file already exists there.
try:
with open(pidfile, 'x') as f:
# Successfully opened a new file. Since the file is new
# there is no concurrent process. Write our pid.
f.write(str(mypid))
atexit.register(clear_my_pid, pidfile)
return
except FileExistsError:
# The pid file already exixts, but it may contain a stale
# pid of a terminated process.
with open(pidfile, 'r+') as f:
# Read the pid in the file.
existing_pid = None
try:
existing_pid = int(f.read().strip())
except ValueError:
pass # No valid integer in the file.
# Check if the pid in it is valid.
if existing_pid:
if is_pid_valid(existing_pid):
print("Another %s is already running (pid %d)." % (name, existing_pid), file=sys.stderr)
sys.exit(1)
# Write our pid.
f.seek(0)
f.write(str(mypid))
f.truncate()
atexit.register(clear_my_pid, pidfile)
def clear_my_pid(pidfile):
import os
os.unlink(pidfile)
def is_pid_valid(pid):
"""Checks whether a pid is a valid process ID of a currently running process."""
# adapted from http://stackoverflow.com/questions/568271/how-to-check-if-there-exists-a-process-with-a-given-pid
import os, errno
if pid <= 0: raise ValueError('Invalid PID.')
try:
os.kill(pid, 0)
except OSError as err:
if err.errno == errno.ESRCH: # No such process
return False
elif err.errno == errno.EPERM: # Not permitted to send signal
return True
else: # EINVAL
raise
else:
return True
def shell(method, cmd_args, env={}, capture_stderr=False):
# A safe way to execute processes.
# Some processes like apt-get require being given a sane PATH.
import subprocess
env.update({ "PATH": "/sbin:/bin:/usr/sbin:/usr/bin" })
stderr = None if not capture_stderr else subprocess.STDOUT
ret = getattr(subprocess, method)(cmd_args, env=env, stderr=stderr)
if isinstance(ret, bytes): ret = ret.decode("utf8")
return ret