view tests/test-batching.py @ 39561:d06834e0f48e

wireprotov2peer: stream decoded responses

Previously, wire protocol version 2 would buffer all response data.
Only once all data was received did we CBOR decode it and resolve
the future associated with the command. This was obviously not
desirable. In future commits that introduce large response payloads,
this caused significant memory bloat and slowed down client
operations due to waiting on the server.

This commit refactors the response handling code so that response
data can be streamed.

Command response objects now contain a buffered CBOR decoder. As
new data arrives, it is fed into the decoder. Decoded objects are
made available to the generator as they are decoded.

Because there is a separate thread processing incoming frames and
feeding data into the response object, there is the potential for
race conditions when mutating response objects. So a lock has been
added to guard access to critical state variables.

Because the generator emitting decoded objects needs to wait on
those objects to become available, we've added an Event for the
generator to wait on so it doesn't busy loop. This does mean
there is the potential for deadlocks. And I'm pretty sure they can
occur in some scenarios. We already have a handful of TODOs around
this. But I've added some more. Fixing this will likely require
moving the background thread receiving frames into clienthandler.
We likely would have done this anyway when implementing the client
bits for the SSH transport.

Test output changes because the initial CBOR map holding the overall
response state is now always handled internally by the response
object.

Differential Revision: https://phab.mercurial-scm.org/D4474

# test-batching.py - tests for transparent command batching
#
# Copyright 2011 Peter Arrenbrecht <[e-mail]>
#
# 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

import contextlib

from mercurial import (
    localrepo,
    wireprotov1peer,

)

# 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

    @contextlib.contextmanager
    def commandexecutor(self):
        e = localrepo.localcommandexecutor(self)
        try:
            yield e
        finally:
            e.close()

# 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 proxied methods.

    with it.commandexecutor() as e:
        ffoo = e.callcommand('foo', {'one': 'One', 'two': 'Two'})
        fbar = e.callcommand('bar', {'b': 'Eins', 'a': 'Zwei'})
        fbar2 = e.callcommand('bar', {'b': 'Uno', 'a': 'Due'})

    print(ffoo.result())
    print(fbar.result())
    print(fbar2.result())

# 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,)])
        for r in res.split(';'):
            yield r

    @contextlib.contextmanager
    def commandexecutor(self):
        e = wireprotov1peer.peerexecutor(self)
        try:
            yield e
        finally:
            e.close()

    @wireprotov1peer.batchable
    def foo(self, one, two=None):
        encargs = [('one', mangle(one),), ('two', mangle(two),)]
        encresref = wireprotov1peer.future()
        yield encargs, encresref
        yield unmangle(encresref.value)

    @wireprotov1peer.batchable
    def bar(self, b, a):
        encresref = wireprotov1peer.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)