Mercurial > hg
view mercurial/lock.py @ 26755:bb0b955d050d
streamclone: support for producing and consuming stream clone bundles
Up to this point, stream clones only existed as a dynamically generated
data format produced and consumed during streaming clones. In order to
support this efficient cloning format with the clone bundles feature, we
need a more formal, on disk representation of the streaming clone data.
This patch introduces a new "bundle" type for streaming clones. Unlike
existing bundles, it does not contain changegroup data. It does,
however, share the same concepts like the 4 byte header which identifies
the type of data that follows and the 2 byte abbreviation for
compression types (of which only "UN" is currently supported).
The new bundle format is essentially the existing stream clone version 1
data format with some headers at the beginning.
Content negotiation at stream clone request time checked for repository
format/requirements compatibility before initiating a stream clone. We
can't do active content negotiation when using clone bundles. So, we put
this set of requirements inside the payload so consumers have a built-in
mechanism for checking compatibility before reading and applying lots of
data. Of course, we will also advertise this requirements set in clone
bundles. But that's for another patch.
We currently don't have a mechanism to produce and consume this new
bundle format. This will be implemented in upcoming patches.
It's worth noting that if a legacy client attempts to `hg unbundle` a
stream clone bundle (with the "HGS1" header), it will abort with:
"unknown bundle version S1," which seems appropriate.
author | Gregory Szorc <gregory.szorc@gmail.com> |
---|---|
date | Sat, 17 Oct 2015 11:14:52 -0700 |
parents | e8564e04382d |
children | 054abf2377e8 |
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# lock.py - simple advisory locking scheme for mercurial # # Copyright 2005, 2006 Matt Mackall <mpm@selenic.com> # # This software may be used and distributed according to the terms of the # GNU General Public License version 2 or any later version. from __future__ import absolute_import import contextlib import errno import os import socket import time import warnings from . import ( error, util, ) class lock(object): '''An advisory lock held by one process to control access to a set of files. Non-cooperating processes or incorrectly written scripts can ignore Mercurial's locking scheme and stomp all over the repository, so don't do that. Typically used via localrepository.lock() to lock the repository store (.hg/store/) or localrepository.wlock() to lock everything else under .hg/.''' # lock is symlink on platforms that support it, file on others. # symlink is used because create of directory entry and contents # are atomic even over nfs. # old-style lock: symlink to pid # new-style lock: symlink to hostname:pid _host = None def __init__(self, vfs, file, timeout=-1, releasefn=None, acquirefn=None, desc=None, inheritchecker=None, parentlock=None): self.vfs = vfs self.f = file self.held = 0 self.timeout = timeout self.releasefn = releasefn self.acquirefn = acquirefn self.desc = desc self._inheritchecker = inheritchecker self.parentlock = parentlock self._parentheld = False self._inherited = False self.postrelease = [] self.pid = self._getpid() self.delay = self.lock() if self.acquirefn: self.acquirefn() def __del__(self): if self.held: warnings.warn("use lock.release instead of del lock", category=DeprecationWarning, stacklevel=2) # ensure the lock will be removed # even if recursive locking did occur self.held = 1 self.release() def _getpid(self): # wrapper around os.getpid() to make testing easier return os.getpid() def lock(self): timeout = self.timeout while True: try: self._trylock() return self.timeout - timeout except error.LockHeld as inst: if timeout != 0: time.sleep(1) if timeout > 0: timeout -= 1 continue raise error.LockHeld(errno.ETIMEDOUT, inst.filename, self.desc, inst.locker) def _trylock(self): if self.held: self.held += 1 return if lock._host is None: lock._host = socket.gethostname() lockname = '%s:%s' % (lock._host, self.pid) retry = 5 while not self.held and retry: retry -= 1 try: self.vfs.makelock(lockname, self.f) self.held = 1 except (OSError, IOError) as why: if why.errno == errno.EEXIST: locker = self._readlock() # special case where a parent process holds the lock -- this # is different from the pid being different because we do # want the unlock and postrelease functions to be called, # but the lockfile to not be removed. if locker == self.parentlock: self._parentheld = True self.held = 1 return locker = self._testlock(locker) if locker is not None: raise error.LockHeld(errno.EAGAIN, self.vfs.join(self.f), self.desc, locker) else: raise error.LockUnavailable(why.errno, why.strerror, why.filename, self.desc) def _readlock(self): """read lock and return its value Returns None if no lock exists, pid for old-style locks, and host:pid for new-style locks. """ try: return self.vfs.readlock(self.f) except (OSError, IOError) as why: if why.errno == errno.ENOENT: return None raise def _testlock(self, locker): if locker is None: return None try: host, pid = locker.split(":", 1) except ValueError: return locker if host != lock._host: return locker try: pid = int(pid) except ValueError: return locker if util.testpid(pid): return locker # if locker dead, break lock. must do this with another lock # held, or can race and break valid lock. try: l = lock(self.vfs, self.f + '.break', timeout=0) self.vfs.unlink(self.f) l.release() except error.LockError: return locker def testlock(self): """return id of locker if lock is valid, else None. If old-style lock, we cannot tell what machine locker is on. with new-style lock, if locker is on this machine, we can see if locker is alive. If locker is on this machine but not alive, we can safely break lock. The lock file is only deleted when None is returned. """ locker = self._readlock() return self._testlock(locker) @contextlib.contextmanager def inherit(self): """context for the lock to be inherited by a Mercurial subprocess. Yields a string that will be recognized by the lock in the subprocess. Communicating this string to the subprocess needs to be done separately -- typically by an environment variable. """ if not self.held: raise error.LockInheritanceContractViolation( 'inherit can only be called while lock is held') if self._inherited: raise error.LockInheritanceContractViolation( 'inherit cannot be called while lock is already inherited') if self._inheritchecker is not None: self._inheritchecker() if self.releasefn: self.releasefn() if self._parentheld: lockname = self.parentlock else: lockname = '%s:%s' % (lock._host, self.pid) self._inherited = True try: yield lockname finally: if self.acquirefn: self.acquirefn() self._inherited = False def release(self): """release the lock and execute callback function if any If the lock has been acquired multiple times, the actual release is delayed to the last release call.""" if self.held > 1: self.held -= 1 elif self.held == 1: self.held = 0 if self._getpid() != self.pid: # we forked, and are not the parent return try: if self.releasefn: self.releasefn() finally: if not self._parentheld: try: self.vfs.unlink(self.f) except OSError: pass # The postrelease functions typically assume the lock is not held # at all. if not self._parentheld: for callback in self.postrelease: callback() def release(*locks): for lock in locks: if lock is not None: lock.release()