hg: obtain lock when creating share from pooled repo (issue5104)
There are race conditions between clients performing a shared clone
to pooled storage:
1) Clients race to create the new shared repo in the pool directory
2) 1 client is seeding the repo in the pool directory and another goes
to share it before it is fully cloned
We prevent these race conditions by obtaining a lock in the pool
directory that is derived from the name of the repo we will be
accessing.
To test this, a simple generic "lockdelay" extension has been added.
The extension inserts an optional, configurable delay before or after
lock acquisition. In the test, we delay 2 seconds after lock acquisition
in the first process and 1 second before lock acquisition in the 2nd
process. This means the first process has 1s to obtain the lock. There
is a race condition here. If we encounter it in the wild, we could
change the dummy extension to wait on the lock file to appear instead
of relying on timing. But that's more complicated. Let's see what
happens first.
from __future__ import absolute_import
from mercurial import wireproto
class proto(object):
def __init__(self, args):
self.args = args
def getargs(self, spec):
args = self.args
args.setdefault('*', {})
names = spec.split()
return [args[n] for n in names]
class clientpeer(wireproto.wirepeer):
def __init__(self, serverrepo):
self.serverrepo = serverrepo
def _capabilities(self):
return ['batch']
def _call(self, cmd, **args):
return wireproto.dispatch(self.serverrepo, proto(args), cmd)
@wireproto.batchable
def greet(self, name):
f = wireproto.future()
yield {'name': mangle(name)}, f
yield unmangle(f.value)
class serverrepo(object):
def greet(self, name):
return "Hello, " + name
def filtered(self, name):
return self
def mangle(s):
return ''.join(chr(ord(c) + 1) for c in s)
def unmangle(s):
return ''.join(chr(ord(c) - 1) for c in s)
def greet(repo, proto, name):
return mangle(repo.greet(unmangle(name)))
wireproto.commands['greet'] = (greet, 'name',)
srv = serverrepo()
clt = clientpeer(srv)
print clt.greet("Foobar")
b = clt.batch()
fs = [b.greet(s) for s in ["Fo, =;:<o", "Bar"]]
b.submit()
print [f.value for f in fs]