Fix hg clone race with writer
Most read operations in hg don't need locks because we order reads and
writes for consistency. Clone is an exception to this as we're copying
entire file histories and could end up with more file history copied
than we have commits.
For now, make clone take a lock on the source repo. Non-hardlinked
clone should eventually be changed to use lockless pull.
# lock.py - simple locking scheme for mercurial
#
# Copyright 2005 Matt Mackall <mpm@selenic.com>
#
# This software may be used and distributed according to the terms
# of the GNU General Public License, incorporated herein by reference.
import os, time
import util
class LockHeld(Exception):
pass
class lock:
def __init__(self, file, wait = 1):
self.f = file
self.held = 0
self.wait = wait
self.lock()
def __del__(self):
self.release()
def lock(self):
while 1:
try:
self.trylock()
return 1
except LockHeld, inst:
if self.wait:
time.sleep(1)
continue
raise inst
def trylock(self):
pid = os.getpid()
try:
util.makelock(str(pid), self.f)
self.held = 1
except (OSError, IOError):
raise LockHeld(util.readlock(self.f))
def release(self):
if self.held:
self.held = 0
try:
os.unlink(self.f)
except: pass