mercurial/lock.py

copies: avoid instancing more changectx to access parent revisions

We just need to know the revision numbers of the parents, creating full context
is needlessly expensive.

This provide a small, but noticeable performance boost.

revision: large amount; added files: large amount; rename small amount; c3b14617fbd7 9ba6ab77fd29
before: ! wall 2.885636 comb 2.900000 user 2.870000 sys 0.030000 (median of 10)
after:  ! wall 2.702270 comb 2.710000 user 2.690000 sys 0.020000 (median of 10)
revision: large amount; added files: small amount; rename small amount; c3b14617fbd7 f650a9b140d2
before: ! wall 4.298271 comb 4.290000 user 4.240000 sys 0.050000 (median of 10)
after:  ! wall 3.976610 comb 3.970000 user 3.920000 sys 0.050000 (median of 10)
revision: large amount; added files: large amount; rename large amount; 08ea3258278e d9fa043f30c0
before: ! wall 0.773397 comb 0.770000 user 0.770000 sys 0.000000 (median of 11)
after:  ! wall 0.701634 comb 0.700000 user 0.700000 sys 0.000000 (median of 13)
revision: small amount; added files: large amount; rename large amount; df6f7a526b60 a83dc6a2d56f
before: ! wall 0.013585 comb 0.010000 user 0.010000 sys 0.000000 (median of 217)
after:  ! wall 0.013550 comb 0.010000 user 0.010000 sys 0.000000 (median of 218)
revision: small amount; added files: large amount; rename small amount; 4aa4e1f8e19a 169138063d63
before: ! wall 0.003202 comb 0.000000 user 0.000000 sys 0.000000 (median of 929)
after:  ! wall 0.002993 comb 0.010000 user 0.010000 sys 0.000000 (median of 992)
revision: small amount; added files: small amount; rename small amount; 4bc173b045a6 964879152e2e
before: ! wall 0.000077 comb 0.000000 user 0.000000 sys 0.000000 (median of 12060)
after:  ! wall 0.000072 comb 0.000000 user 0.000000 sys 0.000000 (median of 12804)
revision: medium amount; added files: large amount; rename medium amount; c95f1ced15f2 2c68e87c3efe
before: ! wall 0.510614 comb 0.500000 user 0.500000 sys 0.000000 (median of 18)
after:  ! wall 0.473681 comb 0.470000 user 0.470000 sys 0.000000 (median of 20)
revision: medium amount; added files: medium amount; rename small amount; d343da0c55a8 d7746d32bf9d
before: ! wall 0.126552 comb 0.130000 user 0.130000 sys 0.000000 (median of 77)
after:  ! wall 0.115240 comb 0.110000 user 0.110000 sys 0.000000 (median of 85)

Differential Revision: https://phab.mercurial-scm.org/D7122

# 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.

from __future__ import absolute_import

import contextlib
import errno
import os
import signal
import socket
import time
import warnings

from .i18n import _
from .pycompat import getattr

from . import (
    encoding,
    error,
    pycompat,
    util,
)

from .utils import procutil


def _getlockprefix():
    """Return a string which is used to differentiate pid namespaces

    It's useful to detect "dead" processes and remove stale locks with
    confidence. Typically it's just hostname. On modern linux, we include an
    extra Linux-specific pid namespace identifier.
    """
    result = encoding.strtolocal(socket.gethostname())
    if pycompat.sysplatform.startswith(b'linux'):
        try:
            result += b'/%x' % os.stat(b'/proc/self/ns/pid').st_ino
        except OSError as ex:
            if ex.errno not in (errno.ENOENT, errno.EACCES, errno.ENOTDIR):
                raise
    return result


@contextlib.contextmanager
def _delayedinterrupt():
    """Block signal interrupt while doing something critical

    This makes sure that the code block wrapped by this context manager won't
    be interrupted.

    For Windows developers: It appears not possible to guard time.sleep()
    from CTRL_C_EVENT, so please don't use time.sleep() to test if this is
    working.
    """
    assertedsigs = []
    blocked = False
    orighandlers = {}

    def raiseinterrupt(num):
        if num == getattr(signal, 'SIGINT', None) or num == getattr(
            signal, 'CTRL_C_EVENT', None
        ):
            raise KeyboardInterrupt
        else:
            raise error.SignalInterrupt

    def catchterm(num, frame):
        if blocked:
            assertedsigs.append(num)
        else:
            raiseinterrupt(num)

    try:
        # save handlers first so they can be restored even if a setup is
        # interrupted between signal.signal() and orighandlers[] =.
        for name in [
            b'CTRL_C_EVENT',
            b'SIGINT',
            b'SIGBREAK',
            b'SIGHUP',
            b'SIGTERM',
        ]:
            num = getattr(signal, name, None)
            if num and num not in orighandlers:
                orighandlers[num] = signal.getsignal(num)
        try:
            for num in orighandlers:
                signal.signal(num, catchterm)
        except ValueError:
            pass  # in a thread? no luck

        blocked = True
        yield
    finally:
        # no simple way to reliably restore all signal handlers because
        # any loops, recursive function calls, except blocks, etc. can be
        # interrupted. so instead, make catchterm() raise interrupt.
        blocked = False
        try:
            for num, handler in orighandlers.items():
                signal.signal(num, handler)
        except ValueError:
            pass  # in a thread?

    # re-raise interrupt exception if any, which may be shadowed by a new
    # interrupt occurred while re-raising the first one
    if assertedsigs:
        raiseinterrupt(assertedsigs[0])


def trylock(ui, vfs, lockname, timeout, warntimeout, *args, **kwargs):
    """return an acquired lock or raise an a LockHeld exception

    This function is responsible to issue warnings and or debug messages about
    the held lock while trying to acquires it."""

    def printwarning(printer, locker):
        """issue the usual "waiting on lock" message through any channel"""
        # show more details for new-style locks
        if b':' in locker:
            host, pid = locker.split(b":", 1)
            msg = _(
                b"waiting for lock on %s held by process %r on host %r\n"
            ) % (
                pycompat.bytestr(l.desc),
                pycompat.bytestr(pid),
                pycompat.bytestr(host),
            )
        else:
            msg = _(b"waiting for lock on %s held by %r\n") % (
                l.desc,
                pycompat.bytestr(locker),
            )
        printer(msg)

    l = lock(vfs, lockname, 0, *args, dolock=False, **kwargs)

    debugidx = 0 if (warntimeout and timeout) else -1
    warningidx = 0
    if not timeout:
        warningidx = -1
    elif warntimeout:
        warningidx = warntimeout

    delay = 0
    while True:
        try:
            l._trylock()
            break
        except error.LockHeld as inst:
            if delay == debugidx:
                printwarning(ui.debug, inst.locker)
            if delay == warningidx:
                printwarning(ui.warn, inst.locker)
            if timeout <= delay:
                raise error.LockHeld(
                    errno.ETIMEDOUT, inst.filename, l.desc, inst.locker
                )
            time.sleep(1)
            delay += 1

    l.delay = delay
    if l.delay:
        if 0 <= warningidx <= l.delay:
            ui.warn(_(b"got lock after %d seconds\n") % l.delay)
        else:
            ui.debug(b"got lock after %d seconds\n" % l.delay)
    if l.acquirefn:
        l.acquirefn()
    return l


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,
        fname,
        timeout=-1,
        releasefn=None,
        acquirefn=None,
        desc=None,
        inheritchecker=None,
        parentlock=None,
        signalsafe=True,
        dolock=True,
    ):
        self.vfs = vfs
        self.f = fname
        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
        if signalsafe:
            self._maybedelayedinterrupt = _delayedinterrupt
        else:
            self._maybedelayedinterrupt = util.nullcontextmanager
        self.postrelease = []
        self.pid = self._getpid()
        if dolock:
            self.delay = self.lock()
            if self.acquirefn:
                self.acquirefn()

    def __enter__(self):
        return self

    def __exit__(self, exc_type, exc_value, exc_tb):
        self.release()

    def __del__(self):
        if self.held:
            warnings.warn(
                r"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 procutil.getpid() to make testing easier
        return procutil.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 = _getlockprefix()
        lockname = b'%s:%d' % (lock._host, self.pid)
        retry = 5
        while not self.held and retry:
            retry -= 1
            try:
                with self._maybedelayedinterrupt():
                    self.vfs.makelock(lockname, self.f)
                    self.held = 1
            except (OSError, IOError) as why:
                if why.errno == errno.EEXIST:
                    locker = self._readlock()
                    if locker is None:
                        continue

                    # 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
                    )

        if not self.held:
            # use empty locker to mean "busy for frequent lock/unlock
            # by many processes"
            raise error.LockHeld(
                errno.EAGAIN, self.vfs.join(self.f), self.desc, b""
            )

    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(b":", 1)
        except ValueError:
            return locker
        if host != lock._host:
            return locker
        try:
            pid = int(pid)
        except ValueError:
            return locker
        if procutil.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 + b'.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(
                b'inherit can only be called while lock is held'
            )
        if self._inherited:
            raise error.LockInheritanceContractViolation(
                b'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 = b'%s:%d' % (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()
                # Prevent double usage and help clear cycles.
                self.postrelease = None


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