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# This Source Code Form is subject to the terms of the Mozilla Public
# License, v. 2.0. If a copy of the MPL was not distributed with this file,
# This file contains miscellaneous utility functions that don't belong anywhere
# in particular.
import errno
import os
import stat
import sys
import time
class LockFile(object):
"""LockFile is used by the lock_file method to hold the lock.
This object should not be used directly, but only through
the lock_file method below.
"""
def __init__(self, lockfile):
self.lockfile = lockfile
def __del__(self):
while True:
try:
os.remove(self.lockfile)
break
except OSError as e:
if e.errno == errno.EACCES:
# Another process probably has the file open, we'll retry.
# Just a short sleep since we want to drop the lock ASAP
# (but we need to let some other process close the file
# first).
time.sleep(0.1)
else:
# Re-raise unknown errors
raise
def lock_file(lockfile, max_wait=600):
"""Create and hold a lockfile of the given name, with the given timeout.
To release the lock, delete the returned object.
"""
# FUTURE This function and object could be written as a context manager.
while True:
try:
fd = os.open(lockfile, os.O_EXCL | os.O_RDWR | os.O_CREAT)
# We created the lockfile, so we're the owner
break
except OSError as e:
if e.errno == errno.EEXIST or (
sys.platform == "win32" and e.errno == errno.EACCES
):
pass
else:
# Should not occur
raise
try:
# The lock file exists, try to stat it to get its age
# and read its contents to report the owner PID
f = open(lockfile, "r")
s = os.stat(lockfile)
except EnvironmentError as e:
if e.errno == errno.ENOENT or e.errno == errno.EACCES:
# We didn't create the lockfile, so it did exist, but it's
# gone now. Just try again
continue
raise Exception(
"{0} exists but stat() failed: {1}".format(lockfile, e.strerror)
)
# We didn't create the lockfile and it's still there, check
# its age
now = int(time.time())
if now - s[stat.ST_MTIME] > max_wait:
pid = f.readline().rstrip()
raise Exception(
"{0} has been locked for more than "
"{1} seconds (PID {2})".format(lockfile, max_wait, pid)
)
# It's not been locked too long, wait a while and retry
f.close()
time.sleep(1)
# if we get here. we have the lockfile. Convert the os.open file
# descriptor into a Python file object and record our PID in it
f = os.fdopen(fd, "w")
f.write("{0}\n".format(os.getpid()))
f.close()
return LockFile(lockfile)