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