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# Copyright (C) 2006, 2007, 2008, 2009 Canonical Ltd
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# Copyright (C) 2006 Canonical Ltd
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# This program is free software; you can redistribute it and/or modify
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# it under the terms of the GNU General Public License as published by
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# the Free Software Foundation; either version 2 of the License, or
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# (at your option) any later version.
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# This program is distributed in the hope that it will be useful,
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# but WITHOUT ANY WARRANTY; without even the implied warranty of
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# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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# GNU General Public License for more details.
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# You should have received a copy of the GNU General Public License
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# along with this program; if not, write to the Free Software
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# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
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# Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
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"""On-disk mutex protecting a resource
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>>> t = MemoryTransport()
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>>> l = LockDir(t, 'sample-lock')
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>>> token = l.wait_lock()
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>>> # do something here
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# TODO: We sometimes have the problem that our attempt to rename '1234' to
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# 'held' fails because the transport server moves into an existing directory,
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# rather than failing the rename. If we made the info file name the same as
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# the locked directory name we would avoid this problem because moving into
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# the held directory would implicitly clash. However this would not mesh with
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# the existing locking code and needs a new format of the containing object.
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# -- robertc, mbp 20070628
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from StringIO import StringIO
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import bzrlib.config
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from bzrlib.decorators import only_raises
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from bzrlib.errors import (
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DirectoryNotEmpty,
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LockBreakMismatch,
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from bzrlib.trace import mutter, note
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from bzrlib.osutils import format_delta, rand_chars, get_host_name
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from bzrlib.lazy_import import lazy_import
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lazy_import(globals(), """
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from bzrlib import rio
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from bzrlib.trace import mutter
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from bzrlib.transport import Transport
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from bzrlib.osutils import rand_chars
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from bzrlib.rio import RioWriter, read_stanza, Stanza
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# XXX: At the moment there is no consideration of thread safety on LockDir
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# objects. This should perhaps be updated - e.g. if two threads try to take a
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def create(self, mode=None):
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"""Create the on-disk lock.
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This is typically only called when the object/directory containing the
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This is typically only called when the object/directory containing the
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directory is first created. The lock is not held when it's created.
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self._trace("create lock directory")
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self.transport.mkdir(self.path, mode=mode)
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except (TransportError, PathError), e:
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raise LockFailed(self, e)
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def _attempt_lock(self):
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"""Make the pending directory and attempt to rename into place.
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If the rename succeeds, we read back the info file to check that we
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If we fail to acquire the lock, this method is responsible for
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cleaning up the pending directory if possible. (But it doesn't do
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:returns: The nonce of the lock, if it was successfully acquired.
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:raises LockContention: If the lock is held by someone else. The exception
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contains the info of the current holder of the lock.
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if self.transport.is_readonly():
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raise UnlockableTransport(self.transport)
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self.transport.mkdir(self.path, mode=mode)
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def attempt_lock(self):
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"""Take the lock; fail if it's already held.
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If you wish to block until the lock can be obtained, call wait_lock()
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self._trace("lock_write...")
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start_time = time.time()
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tmpname = self._create_pending_dir()
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except (errors.TransportError, PathError), e:
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self._trace("... failed to create pending dir, %s", e)
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raise LockFailed(self, e)
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if self._fake_read_lock:
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raise LockContention(self)
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if self.transport.is_readonly():
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raise UnlockableTransport(self.transport)
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tmpname = '%s/pending.%s.tmp' % (self.path, rand_chars(20))
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self.transport.mkdir(tmpname)
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self._prepare_info(sio)
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# append will create a new file; we use append rather than put
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# because we don't want to write to a temporary file and rename
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# into place, because that's going to happen to the whole
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self.transport.append(tmpname + self.__INFO_NAME, sio)
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self.transport.rename(tmpname, self._held_dir)
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except (errors.TransportError, PathError, DirectoryNotEmpty,
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FileExists, ResourceBusy), e:
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self._trace("... contention, %s", e)
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self._remove_pending_dir(tmpname)
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raise LockContention(self)
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self._trace("... lock failed, %s", e)
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self._remove_pending_dir(tmpname)
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# We must check we really got the lock, because Launchpad's sftp
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# server at one time had a bug were the rename would successfully
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# move the new directory into the existing directory, which was
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# incorrect. It's possible some other servers or filesystems will
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# have a similar bug allowing someone to think they got the lock
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# when it's already held.
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# See <https://bugs.edge.launchpad.net/bzr/+bug/498378> for one case.
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# Strictly the check is unnecessary and a waste of time for most
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# people, but probably worth trapping if something is wrong.
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self._trace("after locking, info=%r", info)
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raise LockFailed(self, "lock was renamed into place, but "
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if info['nonce'] != self.nonce:
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self._trace("rename succeeded, "
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"but lock is still held by someone else")
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raise LockContention(self)
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self._lock_held = True
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self._trace("... lock succeeded after %dms",
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(time.time() - start_time) * 1000)
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def _remove_pending_dir(self, tmpname):
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"""Remove the pending directory
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This is called if we failed to rename into place, so that the pending
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dirs don't clutter up the lockdir.
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self._trace("remove %s", tmpname)
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self.transport.delete(tmpname + self.__INFO_NAME)
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self.transport.rmdir(tmpname)
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note("error removing pending lock: %s", e)
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def _create_pending_dir(self):
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tmpname = '%s/%s.tmp' % (self.path, rand_chars(10))
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self.transport.mkdir(tmpname)
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# This may raise a FileExists exception
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# which is okay, it will be caught later and determined
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# to be a LockContention.
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self._trace("lock directory does not exist, creating it")
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self.create(mode=self._dir_modebits)
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# After creating the lock directory, try again
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self.transport.mkdir(tmpname)
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self.nonce = rand_chars(20)
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info_bytes = self._prepare_info()
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# We use put_file_non_atomic because we just created a new unique
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# directory so we don't have to worry about files existing there.
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# We'll rename the whole directory into place to get atomic
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self.transport.put_bytes_non_atomic(tmpname + self.__INFO_NAME,
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@only_raises(LockNotHeld, LockBroken)
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self._lock_held = True
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except (PathError, DirectoryNotEmpty, FileExists, ResourceBusy), e:
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mutter("contention on %r: %s", self, e)
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raise LockContention(self)
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def unlock(self):
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"""Release a held lock
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self._fake_read_lock = False
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if not self._lock_held:
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return lock.cant_unlock_not_held(self)
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if self._locked_via_token:
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self._locked_via_token = False
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self._lock_held = False
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old_nonce = self.nonce
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# rename before deleting, because we can't atomically remove the
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start_time = time.time()
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self._trace("unlocking")
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tmpname = '%s/releasing.%s.tmp' % (self.path, rand_chars(20))
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# gotta own it to unlock
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self.transport.rename(self._held_dir, tmpname)
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self._lock_held = False
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self.transport.delete(tmpname + self.__INFO_NAME)
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self.transport.rmdir(tmpname)
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except DirectoryNotEmpty, e:
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# There might have been junk left over by a rename that moved
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# another locker within the 'held' directory. do a slower
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# deletion where we list the directory and remove everything
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# Maybe this should be broader to allow for ftp servers with
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# non-specific error messages?
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self._trace("doing recursive deletion of non-empty directory "
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self.transport.delete_tree(tmpname)
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self._trace("... unlock succeeded after %dms",
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(time.time() - start_time) * 1000)
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result = lock.LockResult(self.transport.abspath(self.path),
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for hook in self.hooks['lock_released']:
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raise LockNotHeld(self)
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# rename before deleting, because we can't atomically remove the whole
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tmpname = '%s/releasing.%s.tmp' % (self.path, rand_chars(20))
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# gotta own it to unlock
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self.transport.rename(self._held_dir, tmpname)
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self._lock_held = False
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self.transport.delete(tmpname + self.__INFO_NAME)
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self.transport.rmdir(tmpname)
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def break_lock(self):
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"""Break a lock not held by this instance of LockDir.
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if info.get('nonce') != self.nonce:
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# there is a lock, but not ours
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raise LockBroken(self)
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def _read_info_file(self, path):
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"""Read one given info file.
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peek() reads the info file of the lock holder, if any.
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return self._parse_info(self.transport.get_bytes(path))
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return self._parse_info(self.transport.get(path))
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"""Check if the lock is held by anyone.
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If it is held, this returns the lock info structure as a rio Stanza,
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which contains some information about the current lock holder.
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Otherwise returns None.
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info = self._read_info_file(self._held_info_path)
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self._trace("peek -> held")
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assert isinstance(info, dict), \
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"bad parse result %r" % info
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except NoSuchFile, e:
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self._trace("peek -> not held")
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def _prepare_info(self):
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def _prepare_info(self, outf):
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"""Write information about a pending lock to a temporary file.
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# XXX: is creating this here inefficient?
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config = bzrlib.config.GlobalConfig()
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user = config.user_email()
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except errors.NoEmailInUsername:
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user = config.username()
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s = rio.Stanza(hostname=get_host_name(),
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s = Stanza(hostname=socket.gethostname(),
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pid=str(os.getpid()),
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start_time=str(int(time.time())),
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nonce=self.nonce,
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user=config.user_email(),
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def _parse_info(self, info_bytes):
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# TODO: Handle if info_bytes is empty
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return rio.read_stanza(osutils.split_lines(info_bytes)).as_dict()
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def attempt_lock(self):
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"""Take the lock; fail if it's already held.
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If you wish to block until the lock can be obtained, call wait_lock()
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:return: The lock token.
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:raises LockContention: if the lock is held by someone else.
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if self._fake_read_lock:
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raise LockContention(self)
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result = self._attempt_lock()
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hook_result = lock.LockResult(self.transport.abspath(self.path),
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for hook in self.hooks['lock_acquired']:
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def wait_lock(self, timeout=None, poll=None, max_attempts=None):
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RioWriter(outf).write_stanza(s)
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def _parse_info(self, info_file):
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return read_stanza(info_file.readlines()).as_dict()
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def wait_lock(self, timeout=_DEFAULT_TIMEOUT_SECONDS,
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poll=_DEFAULT_POLL_SECONDS):
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"""Wait a certain period for a lock.
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If the lock can be acquired within the bounded time, it
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is raised. Either way, this function should return within
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approximately `timeout` seconds. (It may be a bit more if
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a transport operation takes a long time to complete.)
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:param timeout: Approximate maximum amount of time to wait for the
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:param poll: Delay in seconds between retrying the lock.
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:param max_attempts: Maximum number of times to try to lock.
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:return: The lock token.
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timeout = _DEFAULT_TIMEOUT_SECONDS
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poll = _DEFAULT_POLL_SECONDS
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# XXX: the transport interface doesn't let us guard against operations
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# there taking a long time, so the total elapsed time or poll interval
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# may be more than was requested.
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# XXX: the transport interface doesn't let us guard
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# against operations there taking a long time.
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deadline = time.time() + timeout
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return self.attempt_lock()
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except LockContention:
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# possibly report the blockage, then try again
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# TODO: In a few cases, we find out that there's contention by
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# reading the held info and observing that it's not ours. In
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# those cases it's a bit redundant to read it again. However,
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# the normal case (??) is that the rename fails and so we
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# don't know who holds the lock. For simplicity we peek
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new_info = self.peek()
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if new_info is not None and new_info != last_info:
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if last_info is None:
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start = 'Unable to obtain'
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start = 'Lock owner changed for'
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formatted_info = self._format_lock_info(new_info)
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if deadline_str is None:
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deadline_str = time.strftime('%H:%M:%S',
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time.localtime(deadline))
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lock_url = self.transport.abspath(self.path)
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# See <https://bugs.edge.launchpad.net/bzr/+bug/250451>
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# the URL here is sometimes not one that is useful to the
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# user, perhaps being wrapped in a lp-%d or chroot decorator,
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# especially if this error is issued from the server.
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self._report_function('%s %s\n'
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'%s\n' # locked ... ago
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'Will continue to try until %s, unless '
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'you press Ctrl-C.\n'
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'See "bzr help break-lock" for more.',
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if (max_attempts is not None) and (attempt_count >= max_attempts):
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self._trace("exceeded %d attempts")
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raise LockContention(self)
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if time.time() + poll < deadline:
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self._trace("waiting %ss", poll)
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self._trace("timeout after waiting %ss", timeout)
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raise LockContention(self)
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def leave_in_place(self):
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self._locked_via_token = True
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def dont_leave_in_place(self):
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self._locked_via_token = False
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def lock_write(self, token=None):
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"""Wait for and acquire the lock.
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:param token: if this is already locked, then lock_write will fail
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unless the token matches the existing lock.
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:returns: a token if this instance supports tokens, otherwise None.
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:raises TokenLockingNotSupported: when a token is given but this
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instance doesn't support using token locks.
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:raises MismatchedToken: if the specified token doesn't match the token
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of the existing lock.
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A token should be passed in if you know that you have locked the object
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some other way, and need to synchronise this object's state with that
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XXX: docstring duplicated from LockableFiles.lock_write.
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if token is not None:
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self.validate_token(token)
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self._lock_held = True
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self._locked_via_token = True
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return self.wait_lock()
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def lock_write(self):
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"""Wait for and acquire the lock."""
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def lock_read(self):
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"""Compatibility-mode shared lock.
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LockDir doesn't support shared read-only locks, so this
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LockDir doesn't support shared read-only locks, so this
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just pretends that the lock is taken but really does nothing.
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# At the moment Branches are commonly locked for read, but
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# At the moment Branches are commonly locked for read, but
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# we can't rely on that remotely. Once this is cleaned up,
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# reenable this warning to prevent it coming back in
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# reenable this warning to prevent it coming back in
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# -- mbp 20060303
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## warn("LockDir.lock_read falls back to write lock")
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if self._lock_held or self._fake_read_lock:
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raise LockContention(self)
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self._fake_read_lock = True
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def _format_lock_info(self, info):
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"""Turn the contents of peek() into something for the user"""
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lock_url = self.transport.abspath(self.path)
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delta = time.time() - int(info['start_time'])
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'lock %s' % (lock_url,),
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'held by %(user)s on host %(hostname)s [process #%(pid)s]' % info,
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'locked %s' % (format_delta(delta),),
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def validate_token(self, token):
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if token is not None:
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lock_token = info.get('nonce')
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if token != lock_token:
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raise errors.TokenMismatch(token, lock_token)
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self._trace("revalidated by token %r", token)
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def _trace(self, format, *args):
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if 'lock' not in debug.debug_flags:
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mutter(str(self) + ": " + (format % args))
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def wait(self, timeout=20, poll=0.5):
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"""Wait a certain period for a lock to be released."""
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# XXX: the transport interface doesn't let us guard
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# against operations there taking a long time.
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deadline = time.time() + timeout
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if time.time() + poll < deadline:
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raise LockContention(self)
added
removed
bzrlib/lockdir.py
