commandserver: add new forking server implemented without using SocketServer
SocketServer.ForkingMixIn of Python 2.x has a couple of issues, such as:
- race condition that leads to 100% CPU usage (Python 2.6)
https://bugs.python.org/
issue21491
- can't wait for children belonging to different process groups (Python 2.6)
- leaves at least one zombie process (Python 2.6, 2.7)
https://bugs.python.org/
issue11109
The first two are critical because we do setpgid(0, 0) in child process to
isolate terminal signals. The last one isn't, but ForkingMixIn seems to be
doing silly. So there are two choices:
a) backport and maintain SocketServer until we can drop support for Python 2.x
b) replace SocketServer by simpler one and eliminate glue codes
I chose (b) because it's great time for getting rid of utterly complicated
SocketServer stuff, and preparing for future move towards prefork service.
New unixforkingservice is implemented loosely based on chg
531f8ef64be6. It
is monolithic but much simpler than SocketServer. unixservicehandler provides
customizing points for chg, and it will be shared with future prefork service.
Old unixservice class is still used by chgserver. It will be removed later.
Thanks to Jun Wu for investigating these issues.
# test-batching.py - tests for transparent command batching
#
# Copyright 2011 Peter Arrenbrecht <peter@arrenbrecht.ch>
#
# 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, print_function
from mercurial import (
peer,
wireproto,
)
# equivalent of repo.repository
class thing(object):
def hello(self):
return "Ready."
# equivalent of localrepo.localrepository
class localthing(thing):
def foo(self, one, two=None):
if one:
return "%s and %s" % (one, two,)
return "Nope"
def bar(self, b, a):
return "%s und %s" % (b, a,)
def greet(self, name=None):
return "Hello, %s" % name
def batch(self):
'''Support for local batching.'''
return peer.localbatch(self)
# usage of "thing" interface
def use(it):
# Direct call to base method shared between client and server.
print(it.hello())
# Direct calls to proxied methods. They cause individual roundtrips.
print(it.foo("Un", two="Deux"))
print(it.bar("Eins", "Zwei"))
# Batched call to a couple of (possibly proxied) methods.
batch = it.batch()
# The calls return futures to eventually hold results.
foo = batch.foo(one="One", two="Two")
foo2 = batch.foo(None)
bar = batch.bar("Eins", "Zwei")
# We can call non-batchable proxy methods, but the break the current batch
# request and cause additional roundtrips.
greet = batch.greet(name="John Smith")
# We can also add local methods into the mix, but they break the batch too.
hello = batch.hello()
bar2 = batch.bar(b="Uno", a="Due")
# Only now are all the calls executed in sequence, with as few roundtrips
# as possible.
batch.submit()
# After the call to submit, the futures actually contain values.
print(foo.value)
print(foo2.value)
print(bar.value)
print(greet.value)
print(hello.value)
print(bar2.value)
# local usage
mylocal = localthing()
print()
print("== Local")
use(mylocal)
# demo remoting; mimicks what wireproto and HTTP/SSH do
# shared
def escapearg(plain):
return (plain
.replace(':', '::')
.replace(',', ':,')
.replace(';', ':;')
.replace('=', ':='))
def unescapearg(escaped):
return (escaped
.replace(':=', '=')
.replace(':;', ';')
.replace(':,', ',')
.replace('::', ':'))
# server side
# equivalent of wireproto's global functions
class server(object):
def __init__(self, local):
self.local = local
def _call(self, name, args):
args = dict(arg.split('=', 1) for arg in args)
return getattr(self, name)(**args)
def perform(self, req):
print("REQ:", req)
name, args = req.split('?', 1)
args = args.split('&')
vals = dict(arg.split('=', 1) for arg in args)
res = getattr(self, name)(**vals)
print(" ->", res)
return res
def batch(self, cmds):
res = []
for pair in cmds.split(';'):
name, args = pair.split(':', 1)
vals = {}
for a in args.split(','):
if a:
n, v = a.split('=')
vals[n] = unescapearg(v)
res.append(escapearg(getattr(self, name)(**vals)))
return ';'.join(res)
def foo(self, one, two):
return mangle(self.local.foo(unmangle(one), unmangle(two)))
def bar(self, b, a):
return mangle(self.local.bar(unmangle(b), unmangle(a)))
def greet(self, name):
return mangle(self.local.greet(unmangle(name)))
myserver = server(mylocal)
# local side
# equivalent of wireproto.encode/decodelist, that is, type-specific marshalling
# here we just transform the strings a bit to check we're properly en-/decoding
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)
# equivalent of wireproto.wirerepository and something like http's wire format
class remotething(thing):
def __init__(self, server):
self.server = server
def _submitone(self, name, args):
req = name + '?' + '&'.join(['%s=%s' % (n, v) for n, v in args])
return self.server.perform(req)
def _submitbatch(self, cmds):
req = []
for name, args in cmds:
args = ','.join(n + '=' + escapearg(v) for n, v in args)
req.append(name + ':' + args)
req = ';'.join(req)
res = self._submitone('batch', [('cmds', req,)])
return res.split(';')
def batch(self):
return wireproto.remotebatch(self)
@peer.batchable
def foo(self, one, two=None):
if not one:
yield "Nope", None
encargs = [('one', mangle(one),), ('two', mangle(two),)]
encresref = peer.future()
yield encargs, encresref
yield unmangle(encresref.value)
@peer.batchable
def bar(self, b, a):
encresref = peer.future()
yield [('b', mangle(b),), ('a', mangle(a),)], encresref
yield unmangle(encresref.value)
# greet is coded directly. It therefore does not support batching. If it
# does appear in a batch, the batch is split around greet, and the call to
# greet is done in its own roundtrip.
def greet(self, name=None):
return unmangle(self._submitone('greet', [('name', mangle(name),)]))
# demo remote usage
myproxy = remotething(myserver)
print()
print("== Remote")
use(myproxy)