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# Copyright (C) 2006, 2007 Canonical Ltd
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# Copyright (C) 2006-2010 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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# 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., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
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# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
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"""On-disk mutex protecting a resource
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internal locks (such as flock etc) because they can be seen across all
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transports, including http.
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Objects can be read if there is only physical read access; therefore
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Objects can be read if there is only physical read access; therefore
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readers can never be required to create a lock, though they will
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check whether a writer is using the lock. Writers can't detect
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whether anyone else is reading from the resource as they write.
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The desired characteristics are:
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* Locks are not reentrant. (That is, a client that tries to take a
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* Locks are not reentrant. (That is, a client that tries to take a
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lock it already holds may deadlock or fail.)
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* Stale locks can be guessed at by a heuristic
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* Lost locks can be broken by any client
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and deadlocks will likely occur if the locks are aliased.
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In the future we may add a "freshen" method which can be called
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by a lock holder to check that their lock has not been broken, and to
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by a lock holder to check that their lock has not been broken, and to
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update the timestamp within it.
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from cStringIO import StringIO
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from bzrlib import (
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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.transport import Transport
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from bzrlib.osutils import rand_chars, format_delta
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from bzrlib.rio import read_stanza, Stanza
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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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# 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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# files/dirs created.
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_DEFAULT_TIMEOUT_SECONDS = 300
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_DEFAULT_TIMEOUT_SECONDS = 30
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_DEFAULT_POLL_SECONDS = 1.0
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class LockDir(object):
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"""Write-lock guarding access to data."""
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class LockDir(lock.Lock):
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"""Write-lock guarding access to data.
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__INFO_NAME = '/info'
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:param transport: Transport which will contain the lock
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:param path: Path to the lock within the base directory of the
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:param path: Path to the lock within the base directory of the
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assert isinstance(transport, Transport), \
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("not a transport: %r" % transport)
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self.transport = transport
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self._lock_held = False
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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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# 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.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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info = self.peek()
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self._trace("after locking, info=%r", info)
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if info['nonce'] != self.nonce:
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raise LockFailed(self, "lock was renamed into place, but "
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if info.get('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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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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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._fake_read_lock = False
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if not self._lock_held:
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raise LockNotHeld(self)
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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.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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def break_lock(self):
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"""Break a lock not held by this instance of LockDir.
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This is a UI centric function: it uses the bzrlib.ui.ui_factory to
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prompt for input if a lock is detected and there is any doubt about
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it possibly being still active.
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:returns: LockResult for the broken lock.
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self._check_not_locked()
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holder_info = self.peek()
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holder_info = self.peek()
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except LockCorrupt, e:
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# The lock info is corrupt.
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if bzrlib.ui.ui_factory.get_boolean("Break (corrupt %r)" % (self,)):
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self.force_break_corrupt(e.file_data)
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if holder_info is not None:
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lock_info = '\n'.join(self._format_lock_info(holder_info))
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if bzrlib.ui.ui_factory.get_boolean("Break %s" % lock_info):
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self.force_break(holder_info)
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if bzrlib.ui.ui_factory.confirm_action(
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"Break %(lock_info)s", 'bzrlib.lockdir.break',
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dict(lock_info=lock_info)):
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result = self.force_break(holder_info)
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bzrlib.ui.ui_factory.show_message(
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"Broke lock %s" % result.lock_url)
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def force_break(self, dead_holder_info):
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"""Release a lock held by another process.
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LockBreakMismatch is raised.
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After the lock is broken it will not be held by any process.
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It is possible that another process may sneak in and take the
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It is possible that another process may sneak in and take the
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lock before the breaking process acquires it.
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:returns: LockResult for the broken lock.
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if not isinstance(dead_holder_info, dict):
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raise ValueError("dead_holder_info: %r" % dead_holder_info)
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tmpname = '%s/broken.%s.tmp' % (self.path, rand_chars(20))
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self.transport.rename(self._held_dir, tmpname)
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# check that we actually broke the right lock, not someone else;
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# there's a small race window between checking it and doing the
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# there's a small race window between checking it and doing the
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broken_info_path = tmpname + self.__INFO_NAME
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broken_info = self._read_info_file(broken_info_path)
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raise LockBreakMismatch(self, broken_info, dead_holder_info)
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self.transport.delete(broken_info_path)
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self.transport.rmdir(tmpname)
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result = lock.LockResult(self.transport.abspath(self.path),
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current_info.get('nonce'))
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for hook in self.hooks['lock_broken']:
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def force_break_corrupt(self, corrupt_info_lines):
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"""Release a lock that has been corrupted.
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This is very similar to force_break, it except it doesn't assume that
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self.peek() can work.
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:param corrupt_info_lines: the lines of the corrupted info file, used
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to check that the lock hasn't changed between reading the (corrupt)
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info file and calling force_break_corrupt.
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# XXX: this copes with unparseable info files, but what about missing
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# info files? Or missing lock dirs?
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self._check_not_locked()
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tmpname = '%s/broken.%s.tmp' % (self.path, rand_chars(20))
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self.transport.rename(self._held_dir, tmpname)
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# check that we actually broke the right lock, not someone else;
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# there's a small race window between checking it and doing the
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broken_info_path = tmpname + self.__INFO_NAME
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f = self.transport.get(broken_info_path)
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broken_lines = f.readlines()
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if broken_lines != corrupt_info_lines:
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raise LockBreakMismatch(self, broken_lines, corrupt_info_lines)
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self.transport.delete(broken_info_path)
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self.transport.rmdir(tmpname)
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result = lock.LockResult(self.transport.abspath(self.path))
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for hook in self.hooks['lock_broken']:
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def _check_not_locked(self):
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"""If the lock is held by this instance, raise an error."""
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or if the lock has been affected by a bug.
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If the lock is not thought to be held, raises LockNotHeld. If
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the lock is thought to be held but has been broken, raises
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the lock is thought to be held but has been broken, raises
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if not self._lock_held:
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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(path))
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return self._parse_info(self.transport.get_bytes(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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If it is held, this returns the lock info structure as a dict
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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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"""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 = Stanza(hostname=socket.gethostname(),
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except errors.NoWhoami:
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user = osutils.getuser_unicode()
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s = rio.Stanza(hostname=get_host_name(),
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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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return s.to_string()
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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 _parse_info(self, info_bytes):
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lines = osutils.split_lines(info_bytes)
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stanza = rio.read_stanza(lines)
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except ValueError, e:
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mutter('Corrupt lock info file: %r', lines)
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raise LockCorrupt("could not parse lock info file: " + str(e),
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# see bug 185013; we fairly often end up with the info file being
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# empty after an interruption; we could log a message here but
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# there may not be much we can say
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return stanza.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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if self._fake_read_lock:
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raise LockContention(self)
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return self._attempt_lock()
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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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"""Wait a certain period for a lock.
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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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self._report_function('%s %s\n'
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'%s\n' # locked ... ago
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'Will continue to try until %s\n',
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# As local lock urls are correct we display them.
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# We avoid displaying remote lock urls.
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lock_url = self.transport.abspath(self.path)
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if lock_url.startswith('file://'):
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lock_url = lock_url.split('.bzr/')[0]
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user, hostname, pid, time_ago = formatted_info
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msg = ('%s lock %s ' # lock_url
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'[process #%s], ' # pid
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'acquired %s.') # time ago
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msg_args = [start, lock_url, user, hostname, pid, time_ago]
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msg += ('\nWill continue to try until %s, unless '
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msg_args.append(deadline_str)
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msg += '\nSee "bzr help break-lock" for more.'
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self._report_function(msg, *msg_args)
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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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self._trace("waiting %ss", poll)
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# As timeout is always 0 for remote locks
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# this block is applicable only for local
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self._trace("timeout after waiting %ss", timeout)
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raise LockContention(self)
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raise LockContention('(local)', lock_url)
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def leave_in_place(self):
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self._locked_via_token = True
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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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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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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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start_time = info.get('start_time')
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if start_time is None:
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time_ago = '(unknown)'
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time_ago = format_delta(time.time() - int(info['start_time']))
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user = info.get('user', '<unknown>')
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hostname = info.get('hostname', '<unknown>')
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pid = info.get('pid', '<unknown>')
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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):
added
removed
bzrlib/lockdir.py
