mirror of https://github.com/evilhero/mylar
148 lines
3.2 KiB
Python
148 lines
3.2 KiB
Python
"""
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Platform-independent file locking. Inspired by and modeled after zc.lockfile.
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"""
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import os
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try:
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import msvcrt
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except ImportError:
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pass
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try:
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import fcntl
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except ImportError:
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pass
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class LockError(Exception):
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"Could not obtain a lock"
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msg = "Unable to lock %r"
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def __init__(self, path):
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super(LockError, self).__init__(self.msg % path)
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class UnlockError(LockError):
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"Could not release a lock"
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msg = "Unable to unlock %r"
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# first, a default, naive locking implementation
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class LockFile(object):
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"""
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A default, naive locking implementation. Always fails if the file
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already exists.
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"""
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def __init__(self, path):
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self.path = path
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try:
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fd = os.open(path, os.O_CREAT | os.O_WRONLY | os.O_EXCL)
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except OSError:
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raise LockError(self.path)
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os.close(fd)
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def release(self):
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os.remove(self.path)
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def remove(self):
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pass
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class SystemLockFile(object):
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"""
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An abstract base class for platform-specific locking.
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"""
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def __init__(self, path):
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self.path = path
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try:
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# Open lockfile for writing without truncation:
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self.fp = open(path, 'r+')
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except IOError:
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# If the file doesn't exist, IOError is raised; Use a+ instead.
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# Note that there may be a race here. Multiple processes
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# could fail on the r+ open and open the file a+, but only
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# one will get the the lock and write a pid.
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self.fp = open(path, 'a+')
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try:
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self._lock_file()
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except:
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self.fp.seek(1)
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self.fp.close()
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del self.fp
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raise
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self.fp.write(" %s\n" % os.getpid())
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self.fp.truncate()
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self.fp.flush()
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def release(self):
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if not hasattr(self, 'fp'):
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return
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self._unlock_file()
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self.fp.close()
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del self.fp
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def remove(self):
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"""
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Attempt to remove the file
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"""
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try:
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os.remove(self.path)
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except:
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pass
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#@abc.abstract_method
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# def _lock_file(self):
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# """Attempt to obtain the lock on self.fp. Raise LockError if not
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# acquired."""
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def _unlock_file(self):
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"""Attempt to obtain the lock on self.fp. Raise UnlockError if not
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released."""
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class WindowsLockFile(SystemLockFile):
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def _lock_file(self):
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# Lock just the first byte
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try:
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msvcrt.locking(self.fp.fileno(), msvcrt.LK_NBLCK, 1)
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except IOError:
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raise LockError(self.fp.name)
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def _unlock_file(self):
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try:
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self.fp.seek(0)
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msvcrt.locking(self.fp.fileno(), msvcrt.LK_UNLCK, 1)
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except IOError:
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raise UnlockError(self.fp.name)
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if 'msvcrt' in globals():
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LockFile = WindowsLockFile
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class UnixLockFile(SystemLockFile):
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def _lock_file(self):
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flags = fcntl.LOCK_EX | fcntl.LOCK_NB
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try:
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fcntl.flock(self.fp.fileno(), flags)
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except IOError:
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raise LockError(self.fp.name)
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# no need to implement _unlock_file, it will be unlocked on close()
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if 'fcntl' in globals():
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LockFile = UnixLockFile
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