# Copyright (C) 2005, 2006, 2007 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 using OS file locks or file existence. Note: This method of locking is generally deprecated in favour of LockDir, but is used to lock local WorkingTrees, and by some old formats. It's accessed through Transport.lock_read(), etc. 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. That reentrancy is provided by LockableFiles. This defines two classes: ReadLock and WriteLock, which can be implemented in different ways on different platforms. Both have an unlock() method. """ import errno import sys from bzrlib import ( errors, osutils, trace, ) class _base_Lock(object): def __init__(self): self.f = None self.filename = None def _open(self, filename, filemode): self.filename = osutils.realpath(filename) try: self.f = open(self.filename, filemode) return self.f except IOError, e: if e.errno in (errno.EACCES, errno.EPERM): raise errors.ReadOnlyLockError(self.filename, str(e)) if e.errno != errno.ENOENT: raise # maybe this is an old branch (before may 2005) trace.mutter("trying to create missing lock %r", self.filename) self.f = open(self.filename, 'wb+') return self.f def _clear_f(self): """Clear the self.f attribute cleanly.""" if self.f: self.f.close() self.f = None 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() try: import fcntl have_fcntl = True except ImportError: have_fcntl = False try: import win32con, win32file, pywintypes, winerror, msvcrt have_pywin32 = True except ImportError: have_pywin32 = False try: import ctypes, msvcrt have_ctypes = True except ImportError: have_ctypes = False _lock_classes = [] if have_fcntl: LOCK_SH = fcntl.LOCK_SH LOCK_NB = fcntl.LOCK_NB lock_EX = fcntl.LOCK_EX class _fcntl_FileLock(_base_Lock): def _unlock(self): fcntl.lockf(self.f, fcntl.LOCK_UN) self._clear_f() class _fcntl_WriteLock(_fcntl_FileLock): open_locks = {} def __init__(self, filename): # standard IO errors get exposed directly. super(_fcntl_WriteLock, self).__init__() self._open(filename, 'rb+') if self.filename in self.open_locks: self._clear_f() raise errors.LockContention(self.filename) # reserve a slot for this lock - even if the lockf call fails, # at thisi point unlock() will be called, because self.f is set. # TODO: make this fully threadsafe, if we decide we care. self.open_locks[self.filename] = self.filename try: # LOCK_NB will cause IOError to be raised if we can't grab a # lock right away. fcntl.lockf(self.f, fcntl.LOCK_EX | fcntl.LOCK_NB) except IOError, e: if e.errno in (errno.EAGAIN, errno.EACCES): # We couldn't grab the lock self.unlock() # we should be more precise about whats a locking # error and whats a random-other error raise errors.LockError(e) def unlock(self): del self.open_locks[self.filename] self._unlock() class _fcntl_ReadLock(_fcntl_FileLock): open_locks = {} def __init__(self, filename): super(_fcntl_ReadLock, self).__init__() self._open(filename, 'rb') try: # LOCK_NB will cause IOError to be raised if we can't grab a # lock right away. fcntl.lockf(self.f, fcntl.LOCK_SH | fcntl.LOCK_NB) except IOError, e: # we should be more precise about whats a locking # error and whats a random-other error raise errors.LockError(e) def unlock(self): self._unlock() _lock_classes.append(('fcntl', _fcntl_WriteLock, _fcntl_ReadLock)) if have_pywin32 and sys.platform == 'win32': 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): self._open(filename, openmode) self.hfile = msvcrt.get_osfhandle(self.f.fileno()) overlapped = pywintypes.OVERLAPPED() try: win32file.LockFileEx(self.hfile, lockmode, 0, 0x7fff0000, overlapped) except pywintypes.error, e: self._clear_f() if e.args[0] in (winerror.ERROR_LOCK_VIOLATION,): raise errors.LockContention(filename) ## import pdb; pdb.set_trace() raise except Exception, e: self._clear_f() raise errors.LockError(e) def unlock(self): overlapped = pywintypes.OVERLAPPED() try: win32file.UnlockFileEx(self.hfile, 0, 0x7fff0000, overlapped) self._clear_f() except Exception, e: raise errors.LockError(e) class _w32c_ReadLock(_w32c_FileLock): def __init__(self, filename): super(_w32c_ReadLock, self).__init__() self._lock(filename, 'rb', LOCK_SH + LOCK_NB) class _w32c_WriteLock(_w32c_FileLock): def __init__(self, filename): super(_w32c_WriteLock, self).__init__() self._lock(filename, 'rb+', LOCK_EX + LOCK_NB) _lock_classes.append(('pywin32', _w32c_WriteLock, _w32c_ReadLock)) if have_ctypes and sys.platform == 'win32': # These constants were copied from the win32con.py module. LOCKFILE_FAIL_IMMEDIATELY = 1 LOCKFILE_EXCLUSIVE_LOCK = 2 # Constant taken from winerror.py module ERROR_LOCK_VIOLATION = 33 LOCK_SH = 0 LOCK_EX = LOCKFILE_EXCLUSIVE_LOCK LOCK_NB = LOCKFILE_FAIL_IMMEDIATELY _LockFileEx = ctypes.windll.kernel32.LockFileEx _UnlockFileEx = ctypes.windll.kernel32.UnlockFileEx _GetLastError = ctypes.windll.kernel32.GetLastError ### Define the OVERLAPPED structure. # http://msdn2.microsoft.com/en-us/library/ms684342.aspx # typedef struct _OVERLAPPED { # ULONG_PTR Internal; # ULONG_PTR InternalHigh; # union { # struct { # DWORD Offset; # DWORD OffsetHigh; # }; # PVOID Pointer; # }; # HANDLE hEvent; # } OVERLAPPED, class _inner_struct(ctypes.Structure): _fields_ = [('Offset', ctypes.c_uint), # DWORD ('OffsetHigh', ctypes.c_uint), # DWORD ] class _inner_union(ctypes.Union): _fields_ = [('anon_struct', _inner_struct), # struct ('Pointer', ctypes.c_void_p), # PVOID ] class OVERLAPPED(ctypes.Structure): _fields_ = [('Internal', ctypes.c_void_p), # ULONG_PTR ('InternalHigh', ctypes.c_void_p), # ULONG_PTR ('_inner_union', _inner_union), ('hEvent', ctypes.c_void_p), # HANDLE ] class _ctypes_FileLock(_base_Lock): def _lock(self, filename, openmode, lockmode): self._open(filename, openmode) self.hfile = msvcrt.get_osfhandle(self.f.fileno()) overlapped = OVERLAPPED() p_overlapped = ctypes.pointer(overlapped) result = _LockFileEx(self.hfile, # HANDLE hFile lockmode, # DWORD dwFlags 0, # DWORD dwReserved 0x7fffffff, # DWORD nNumberOfBytesToLockLow 0x00000000, # DWORD nNumberOfBytesToLockHigh p_overlapped, # lpOverlapped ) if result == 0: self._clear_f() last_err = _GetLastError() if last_err in (ERROR_LOCK_VIOLATION,): raise errors.LockContention(filename) raise errors.LockError('Unknown locking error: %s' % (last_err,)) def unlock(self): overlapped = OVERLAPPED() p_overlapped = ctypes.pointer(overlapped) result = _UnlockFileEx(self.hfile, # HANDLE hFile 0, # DWORD dwReserved 0x7fffffff, # DWORD nNumberOfBytesToLockLow 0x00000000, # DWORD nNumberOfBytesToLockHigh p_overlapped, # lpOverlapped ) self._clear_f() if result == 0: self._clear_f() last_err = _GetLastError() raise errors.LockError('Unknown unlocking error: %s' % (last_err,)) class _ctypes_ReadLock(_ctypes_FileLock): def __init__(self, filename): super(_ctypes_ReadLock, self).__init__() self._lock(filename, 'rb', LOCK_SH + LOCK_NB) class _ctypes_WriteLock(_ctypes_FileLock): def __init__(self, filename): super(_ctypes_WriteLock, self).__init__() self._lock(filename, 'rb+', LOCK_EX + LOCK_NB) _lock_classes.append(('ctypes', _ctypes_WriteLock, _ctypes_ReadLock)) if len(_lock_classes) == 0: raise NotImplementedError( "We must have one of fcntl, pywin32, or ctypes available" " to support OS locking." ) # We default to using the first available lock class. _lock_type, WriteLock, ReadLock = _lock_classes[0]