context: add specialized way of getting copy source file only
I'm working on support for storing copy metadata in the changeset
instead of the filelog. I don't intend to include the file nodeid
there, but most callers don't need that anyway. This patch introduces
a method similar to ctx.renamed(), but the new method returns only the
source filename, not the nodeid. Subsequent patches will move callers
over to this new method.
Differential Revision: https://phab.mercurial-scm.org/D6008
# extutil.py - useful utility methods for extensions
#
# Copyright 2016 Facebook
#
# 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 time
from mercurial import (
error,
lock as lockmod,
util,
vfs as vfsmod,
)
@contextlib.contextmanager
def flock(lockpath, description, timeout=-1):
"""A flock based lock object. Currently it is always non-blocking.
Note that since it is flock based, you can accidentally take it multiple
times within one process and the first one to be released will release all
of them. So the caller needs to be careful to not create more than one
instance per lock.
"""
# best effort lightweight lock
try:
import fcntl
fcntl.flock
except ImportError:
# fallback to Mercurial lock
vfs = vfsmod.vfs(os.path.dirname(lockpath))
with lockmod.lock(vfs, os.path.basename(lockpath), timeout=timeout):
yield
return
# make sure lock file exists
util.makedirs(os.path.dirname(lockpath))
with open(lockpath, 'a'):
pass
lockfd = os.open(lockpath, os.O_RDONLY, 0o664)
start = time.time()
while True:
try:
fcntl.flock(lockfd, fcntl.LOCK_EX | fcntl.LOCK_NB)
break
except IOError as ex:
if ex.errno == errno.EAGAIN:
if timeout != -1 and time.time() - start > timeout:
raise error.LockHeld(errno.EAGAIN, lockpath, description,
'')
else:
time.sleep(0.05)
continue
raise
try:
yield
finally:
fcntl.flock(lockfd, fcntl.LOCK_UN)
os.close(lockfd)