view mercurial/lock.py @ 14365:a8e3931e3fb5

revlog: linearize created changegroups in generaldelta revlogs

This greatly improves the speed of the bundling process, and often reduces the
bundle size considerably. (Although if the repository is already ordered, this
has little effect on both time and bundle size.)

For non-generaldelta clients, the reduced bundle size translates to a reduced
repository size, similar to shrinking the revlogs (which uses the exact same
algorithm). For generaldelta clients the difference is minor.

When the new bundle format comes, reordering will not be necessary since we
can then store the deltaparent relationsships directly. The eventual default
behavior for clients and servers is presented in the table below, where "new"
implies support for GD as well as the new bundle format:

                    old client                    new client
old server          old bundle, no reorder        old bundle, no reorder
new server, non-GD  old bundle, no reorder[1]     old bundle, no reorder[2]
new server, GD      old bundle, reorder[3]        new bundle, no reorder[4]

[1] reordering is expensive on the server in this case, skip it
[2] client can choose to do its own redelta here
[3] reordering is needed because otherwise the pull does a lot of extra
    work on the server
[4] reordering isn't needed because client can get deltabase in bundle
    format

Currently, the default is to reorder on GD-servers, and not otherwise. A new
setting, bundle.reorder, has been added to override the default reordering
behavior. It can be set to either 'auto' (the default), or any true or false
value as a standard boolean setting, to either force the reordering on or off
regardless of generaldelta.


Some timing data from a relatively branch test repository follows. All
bundling is done with --all --type none options.

Non-generaldelta, non-shrunk repo:
-----------------------------------
Size: 276M

Without reorder (default):
Bundle time: 14.4 seconds
Bundle size: 939M

With reorder:
Bundle time: 1 minute, 29.3 seconds
Bundle size: 381M

Generaldelta, non-shrunk repo:
-----------------------------------
Size: 87M

Without reorder:
Bundle time: 2 minutes, 1.4 seconds
Bundle size: 939M

With reorder (default):
Bundle time: 25.5 seconds
Bundle size: 381M

# lock.py - simple advisory locking scheme for mercurial
#
# Copyright 2005, 2006 Matt Mackall <[e-mail]>
#
# This software may be used and distributed according to the terms of the
# GNU General Public License version 2 or any later version.

import util, error
import errno, os, socket, time
import warnings

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, file, timeout=-1, releasefn=None, desc=None):
        self.f = file
        self.held = 0
        self.timeout = timeout
        self.releasefn = releasefn
        self.desc = desc
        self.lock()

    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 lock(self):
        timeout = self.timeout
        while 1:
            try:
                self.trylock()
                return 1
            except error.LockHeld, 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, os.getpid())
        while not self.held:
            try:
                util.makelock(lockname, self.f)
                self.held = 1
            except (OSError, IOError), why:
                if why.errno == errno.EEXIST:
                    locker = self.testlock()
                    if locker is not None:
                        raise error.LockHeld(errno.EAGAIN, self.f, self.desc,
                                             locker)
                else:
                    raise error.LockUnavailable(why.errno, why.strerror,
                                                why.filename, self.desc)

    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 = util.readlock(self.f)
        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.f + '.break', timeout=0)
            util.unlink(self.f)
            l.release()
        except error.LockError:
            return locker

    def release(self):
        if self.held > 1:
            self.held -= 1
        elif self.held == 1:
            self.held = 0
            if self.releasefn:
                self.releasefn()
            try:
                util.unlink(self.f)
            except OSError:
                pass

def release(*locks):
    for lock in locks:
        if lock is not None:
            lock.release()