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| Current File : //usr/lib64/python2.7/site-packages/mercurial/lock.py |
# 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.
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.postrelease = []
self.pid = os.getpid()
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 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, self.pid)
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.
"""
try:
locker = util.readlock(self.f)
except OSError, 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.f + '.break', timeout=0)
util.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
if self.releasefn:
self.releasefn()
try:
util.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()