# Copyright (C) 2005 Canonical Ltd # This program is free software; you can redistribute it and/or modify # it under the terms of the GNU General Public License as published by # the Free Software Foundation; either version 2 of the License, or # (at your option) any later version. # This program is distributed in the hope that it will be useful, # but WITHOUT ANY WARRANTY; without even the implied warranty of # MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the # GNU General Public License for more details. # You should have received a copy of the GNU General Public License # along with this program; if not, write to the Free Software # Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA """Locking wrappers. This only does local locking using OS locks for now. This module causes two methods, lock() and unlock() to be defined in any way that works on the current platform. It is not specified whether these locks are reentrant (i.e. can be taken repeatedly by a single process) or whether they exclude different threads in a single process. Eventually we may need to use some kind of lock representation that will work on a dumb filesystem without actual locking primitives. This defines two classes: ReadLock and WriteLock, which can be implemented in different ways on different platforms. Both have an unlock() method. """ import sys import os from bzrlib.trace import mutter, note, warning from bzrlib.errors import LockError class _base_Lock(object): def _open(self, filename, filemode): import errno try: self.f = open(filename, filemode) return self.f except IOError, e: if e.errno != errno.ENOENT: raise # maybe this is an old branch (before may 2005) mutter("trying to create missing branch lock %r" % filename) self.f = open(filename, 'wb') return self.f def __del__(self): if self.f: from warnings import warn warn("lock on %r not released" % self.f) self.unlock() def unlock(self): raise NotImplementedError() ############################################################ # msvcrt locks try: import fcntl class _fcntl_FileLock(_base_Lock): f = None def unlock(self): fcntl.flock(self.f, fcntl.LOCK_UN) self.f.close() del self.f class _fcntl_WriteLock(_fcntl_FileLock): def __init__(self, filename): try: fcntl.flock(self._open(filename, 'wb'), fcntl.LOCK_EX) except Exception, e: raise LockError(e) class _fcntl_ReadLock(_fcntl_FileLock): def __init__(self, filename): try: fcntl.flock(self._open(filename, 'rb'), fcntl.LOCK_SH) except Exception, e: raise LockError(e) WriteLock = _fcntl_WriteLock ReadLock = _fcntl_ReadLock except ImportError: try: import win32con, win32file, pywintypes #LOCK_SH = 0 # the default #LOCK_EX = win32con.LOCKFILE_EXCLUSIVE_LOCK #LOCK_NB = win32con.LOCKFILE_FAIL_IMMEDIATELY class _w32c_FileLock(_base_Lock): def _lock(self, filename, openmode, lockmode): try: self._open(filename, openmode) self.hfile = win32file._get_osfhandle(self.f.fileno()) overlapped = pywintypes.OVERLAPPED() win32file.LockFileEx(self.hfile, lockmode, 0, 0x7fff0000, overlapped) except Exception, e: raise LockError(e) def unlock(self): try: overlapped = pywintypes.OVERLAPPED() win32file.UnlockFileEx(self.hfile, 0, 0x7fff0000, overlapped) self.f.close() self.f = None except Exception, e: raise LockError(e) class _w32c_ReadLock(_w32c_FileLock): def __init__(self, filename): _w32c_FileLock._lock(self, filename, 'rb', 0) class _w32c_WriteLock(_w32c_FileLock): def __init__(self, filename): _w32c_FileLock._lock(self, filename, 'wb', win32con.LOCKFILE_EXCLUSIVE_LOCK) WriteLock = _w32c_WriteLock ReadLock = _w32c_ReadLock except ImportError: try: import msvcrt # Unfortunately, msvcrt.locking() doesn't distinguish between # read locks and write locks. Also, the way the combinations # work to get non-blocking is not the same, so we # have to write extra special functions here. class _msvc_FileLock(_base_Lock): LOCK_SH = 1 LOCK_EX = 2 LOCK_NB = 4 def unlock(self): _msvc_unlock(self.f) class _msvc_ReadLock(_msvc_FileLock): def __init__(self, filename): _msvc_lock(self._open(filename, 'rb'), self.LOCK_SH) class _msvc_WriteLock(_msvc_FileLock): def __init__(self, filename): _msvc_lock(self._open(filename, 'wb'), self.LOCK_EX) def _msvc_lock(f, flags): try: # Unfortunately, msvcrt.LK_RLCK is equivalent to msvcrt.LK_LOCK # according to the comments, LK_RLCK is open the lock for writing. # Unfortunately, msvcrt.locking() also has the side effect that it # will only block for 10 seconds at most, and then it will throw an # exception, this isn't terrible, though. if type(f) == file: fpos = f.tell() fn = f.fileno() f.seek(0) else: fn = f fpos = os.lseek(fn, 0,0) os.lseek(fn, 0,0) if flags & _msvc_FileLock.LOCK_SH: if flags & _msvc_FileLock.LOCK_NB: lock_mode = msvcrt.LK_NBLCK else: lock_mode = msvcrt.LK_LOCK elif flags & _msvc_FileLock.LOCK_EX: if flags & _msvc_FileLock.LOCK_NB: lock_mode = msvcrt.LK_NBRLCK else: lock_mode = msvcrt.LK_RLCK else: raise ValueError('Invalid lock mode: %r' % flags) try: msvcrt.locking(fn, lock_mode, -1) finally: os.lseek(fn, fpos, 0) except Exception, e: raise LockError(e) def _msvc_unlock(f): try: if type(f) == file: fpos = f.tell() fn = f.fileno() f.seek(0) else: fn = f fpos = os.lseek(fn, 0,0) os.lseek(fn, 0,0) try: msvcrt.locking(fn, msvcrt.LK_UNLCK, -1) finally: os.lseek(fn, fpos, 0) except Exception, e: raise LockError(e) WriteLock = _msvc_WriteLock ReadLock = _msvc_ReadLock except ImportError: raise NotImplementedError("please write a locking method " "for platform %r" % sys.platform)