view mercurial/lock.py @ 23848:c5456b64eb07

discovery: run discovery on filtered repository

We have been running discovery on unfiltered repository for quite some time.
This was aimed at two things:

- save some bandwith by prevent the repushing of common but hidden changesets
- allow phases changes on secret/hidden changeset on bare push.

The cost of this unfiltered discovery combined with evolution is actually really
high. Evolution likely create thousand of hidden heads, and the discovery is
going to try to discovery if each of them are common or not. For example,
pushing from my development mercurial repository implies 17 discovery
round-trip.

The benefit are rare corner cases while the drawback are massive. So we run the
discovery on a filtered repository again.

We add some hack to detect remote heads that are known locally and adds them to
the common set anyway, so the good behavior of most of the corner case should
remains. But this will not work in all cases.

This bring my discovery phase back from 17 round-trips to 1 or 2.

# 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, vfs, file, timeout=-1, releasefn=None, desc=None):
        self.vfs = vfs
        self.f = file
        self.held = 0
        self.timeout = timeout
        self.releasefn = releasefn
        self.desc = desc
        self.postrelease  = []
        self.pid = os.getpid()
        self.delay = 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 True:
            try:
                self.trylock()
                return self.timeout - timeout
            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, self.pid)
        while not self.held:
            try:
                self.vfs.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.vfs.join(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.

        """
        try:
            locker = self.vfs.readlock(self.f)
        except (OSError, IOError), why:
            if why.errno == errno.ENOENT:
                return None
            raise
        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 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 os.getpid() != self.pid:
                # we forked, and are not the parent
                return
            try:
                if self.releasefn:
                    self.releasefn()
            finally:
                try:
                    self.vfs.unlink(self.f)
                except OSError:
                    pass
            for callback in self.postrelease:
                callback()

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