Created
October 2, 2012 10:53
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Shared/exclusive lock implementation on top of pipes and UNIX file locks
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import os | |
import fcntl | |
import errno | |
from multiprocessing.util import register_after_fork | |
def _reset_level_after_fork(lock): | |
lock._level = 0 | |
class _ShrdExclLock(object): | |
def __init__(self, fd): | |
self._fd = fd | |
self._level = 0 | |
register_after_fork(self, _reset_level_after_fork) | |
def __del__(self): | |
os.close(self._fd) | |
def acquire(self, blocking=True): | |
try: | |
fcntl.lockf(self._fd, self._lock_mode | (not blocking and fcntl.LOCK_NB)) | |
except IOError as e: | |
if e.errno == errno.EAGIN: | |
return False | |
raise | |
self._level += 1 | |
return True | |
def release(self): | |
if self._level == 0: | |
raise ValueError('lock released too many times') | |
self._level -= 1 | |
if self._level == 0: | |
fcntl.lockf(self._fd, fcntl.LOCK_UN) | |
def __enter__(self): | |
self.acquire() | |
return self | |
def __exit__(self, exc_type, exc_value, tb): | |
self.release() | |
class _ShrdLock(_ShrdExclLock): | |
_lock_mode = fcntl.LOCK_SH | |
class _ExclLock(_ShrdExclLock): | |
_lock_mode = fcntl.LOCK_EX | |
def ShrdExclLock(): | |
read_end, write_end = os.pipe() | |
return (_ShrdLock(read_end), _ExclLock(write_end)) |
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