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Howard Stearns 2016-02-07 10:42:43 -08:00
parent 287d91d4b2
commit dc50efe7ec
3 changed files with 386 additions and 257 deletions
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37
examples/entityScripts/tribble.js → examples/entityScripts/tribble.x.34.js
View file

@ -1,5 +1,6 @@
(function () { (function () {
// See tests/performance/tribbles.js // See tests/performance/tribbles.js
Script.include("../libraries/virtualBaton.39.js");
var dimensions, oldColor, entityID, var dimensions, oldColor, entityID,
editRate = 60, editRate = 60,
moveRate = 1, moveRate = 1,
@ -7,7 +8,8 @@
accumulated = 0, accumulated = 0,
increment = {red: 1, green: 1, blue: 1}, increment = {red: 1, green: 1, blue: 1},
hasUpdate = false, hasUpdate = false,
shutdown = false; shutdown = false,
baton;
function nextWavelength(color) { function nextWavelength(color) {
var old = oldColor[color]; var old = oldColor[color];
if (old === 255) { if (old === 255) {
@ -35,6 +37,22 @@
Entities.editEntity(entityID, newData); Entities.editEntity(entityID, newData);
if (!shutdown) { Script.setTimeout(move, nextChange); } if (!shutdown) { Script.setTimeout(move, nextChange); }
} }
function startUpdate() {
print('startUpdate', entityID);
hasUpdate = true;
Script.update.connect(update);
}
function stopUpdate() {
print('stopUpdate', entityID, hasUpdate);
if (!hasUpdate) { return; }
hasUpdate = false;
Script.update.disconnect(update);
}
function stopUpdateAndReclaim() {
print('stopUpdateAndReclaim', entityID);
stopUpdate();
baton.claim(startUpdate, stopUpdateAndReclaim);
}
this.preload = function (givenEntityID) { this.preload = function (givenEntityID) {
entityID = givenEntityID; entityID = givenEntityID;
var properties = Entities.getEntityProperties(entityID); var properties = Entities.getEntityProperties(entityID);
@ -45,11 +63,19 @@
moveRate = (moveRate && userData.moveRate) || moveRate; moveRate = (moveRate && userData.moveRate) || moveRate;
oldColor = properties.color; oldColor = properties.color;
dimensions = Vec3.multiply(scale, properties.dimensions); dimensions = Vec3.multiply(scale, properties.dimensions);
baton = virtualBaton({
// FIXME: batonName: 'io.highfidelity.tribble:' + entityID,
// If we wanted to have only one tribble change colors, we could do:
batonName: 'io.highfidelity.tribble',
instanceId: entityID + MyAvatar.sessionUUID,
debugFlow: true,
debugSend: true,
debugReceive: true
});
if (editTimeout) { if (editTimeout) {
hasUpdate = true; baton.claim(startUpdate, stopUpdateAndReclaim);
Script.update.connect(update);
if (editTimeout > 0) { if (editTimeout > 0) {
Script.setTimeout(function () { Script.update.disconnect(update); hasUpdate = false; }, editTimeout * 1000); Script.setTimeout(stopUpdate, editTimeout * 1000);
} }
} }
if (moveTimeout) { if (moveTimeout) {
@ -60,7 +86,8 @@
} }
}; };
this.unload = function () { this.unload = function () {
baton.unload();
shutdown = true; shutdown = true;
if (hasUpdate) { Script.update.disconnect(update); } stopUpdate();
}; };
}) })

252
examples/libraries/virtualBaton.31.js
View file

@ -1,252 +0,0 @@
"use strict";
/*jslint nomen: true, plusplus: true, vars: true */
/*global Entities, Script, MyAvatar, Messages, AvatarList, print */
//
// Created by Howard Stearns
// Copyright 2016 High Fidelity, Inc.
//
// Distributed under the Apache License, Version 2.0.
// See the accompanying file LICENSE or http://www.apache.org/licenses/LICENSE-2.0.html
//
// Allows cooperating scripts to pass a "virtual baton" between them,
// which is useful when part of a script should only be executed by
// the one participant that is holding this particular baton.
//
// A virtual baton is simply any string agreed upon by the scripts
// that use it. Only one script at a time can hold the baton, and it
// holds it until that script releases it, or the other scripts
// determine that the holding script is not responding. The script
// automatically determines who among claimants has the baton, if anyone,
// and holds an "election" if necessary.
//
// See entityScript/tribble.js as an example, and the functions
// virtualBaton(), claim(), release().
//
// Answers a new virtualBaton for the given parameters, of which 'key'
// is required.
virtualBaton = function virtualBaton(options) {
// Answer averages (number +/- variability). Avoids having everyone act in lockstep.
function randomize(number, variability) {
var randomPart = number * variability;
return number - (randomPart / 2) + (Math.random() * randomPart);
}
var key = options.key,
useOptimizations = (options.useOptimizations === undefined) ? true : options.useOptimizations,
exports = options.exports || {},
electionTimeout = options.electionTimeout || randomize(1000, 0.2), // ms. If no winner in this time, hold a new election.
claimCallback,
releaseCallback,
ourId = MyAvatar.sessionUUID; // better be stable!
if (!key) {
throw new Error("A VirtualBaton must specify a key.");
}
function debug() {
print.apply(null, [].map.call(arguments, JSON.stringify));
}
function debugFlow() {
if (options.debugFlow) { debug.apply(null, arguments); }
}
// Messages: Just synactic sugar for hooking things up to Messages system.
// We create separate subchannel strings for each operation within our general channelKey, instead of using
// a switch in the receiver.
var channelKey = "io.highfidelity.virtualBaton:" + key,
subchannelHandlers = {}, // Message channel string => {function, op}
subchannelKeys = {}; // operation => Message channel string
function subchannelKey(operation) { return channelKey + ':' + operation; }
function receive(operation, handler) { // Record a handler for an operation on our channelKey
var subKey = subchannelKey(operation);
subchannelHandlers[subKey] = {receiver: handler, op: operation};
subchannelKeys[operation] = subKey;
Messages.subscribe(subKey);
}
function sendHelper(subchannel, data) {
var message = JSON.stringify(data);
Messages.sendMessage(subchannel, message);
}
function send1(operation, destination, data) { // Send data for an operation to just one destination on our channelKey.
if (options.debugSend) { debug('baton:', ourId, '=>', destination, operation, data); }
sendHelper(subchannelKey(operation) + destination, data);
}
function send(operation, data) { // Send data for an operation on our channelKey.
if (options.debugSend) { debug('baton:', ourId, '=>', '-', operation, data); }
sendHelper(subchannelKeys[operation], data);
}
Messages.messageReceived.connect(function (channel, messageString, senderID) {
var handler = subchannelHandlers[channel];
if (!handler) { return; }
var data = JSON.parse(messageString);
if (options.debugReceive) { debug('baton:', senderID, '=>', ourId, handler.op, data); }
handler.receiver(data);
});
// Internally, this uses the Paxos algorith to hold elections.
// Alternatively, we could have the message server pick and maintain a winner, but it would
// still have to deal with the same issues of verification in the presence of lost/delayed/reordered messages.
// Paxos is known to be optimal under these circumstances, except that its best to have a dedicated proposer
// (such as the server).
//
// Paxos makes several tests of one "proposal number" versus another, assuming
// that better proposals from the same proposer have a higher number,
// and different proposers use a different set of numbers. We achieve that
// by dividing the "number" into two parts, and integer and a proposerId,
// which keeps the combined number unique and yet still strictly ordered.
function betterNumber(number, best) {
// FIXME restore debug('baton: betterNumber', number, best);
//FIXME return ((number.number || 0) > best.number) && (!best.proposerId || (number.proposerId >= best.proposerId));
return (number.number || 0) > best.number;
}
// Paxos Proposer behavior
var nPromises = 0,
proposalNumber = 0,
nQuorum,
mostRecentInterested,
bestPromise = {number: 0},
electionWatchdog,
recheckInterval = options.recheckInterval || 1000, // ms. Check that winners remain connected. FIXME rnadomize
recheckWatchdog;
function propose() {
debugFlow('baton:', ourId, 'propose', !!claimCallback);
if (electionWatchdog) { Script.clearTimeout(electionWatchdog); }
if (!claimCallback) { return; } // We're not participating.
electionWatchdog = Script.setTimeout(propose, electionTimeout);
nPromises = 0;
proposalNumber = Math.max(proposalNumber, bestPromise.number);
nQuorum = Math.floor(AvatarList.getAvatarIdentifiers().length / 2) + 1; // N.B.: ASSUMES EVERY USER IS RUNNING THE SCRIPT!
send('prepare!', {number: ++proposalNumber, proposerId: ourId});
}
// We create a distinguished promise subchannel for our id, because promises need only be sent to the proposer.
receive('promise' + ourId, function (data) {
if (data.proposerId !== ourId) { return; } // Only the proposer needs to do anything.
mostRecentInterested = mostRecentInterested || data.interested;
if (betterNumber(data, bestPromise)) {
bestPromise = data;
}
if (++nPromises >= nQuorum) {
var answer = {number: data.proposalNumber, proposerId: data.proposerId, winner: data.winner};
if (!answer.winner) { // we get to pick
answer.winner = claimCallback ? ourId : mostRecentInterested;
}
send('accept!', answer);
}
});
// Paxos Acceptor behavior
var bestProposal = {number: 0}, accepted = {};
function acceptedId() { return accepted && accepted.winner; }
receive('prepare!', function (data) {
if (useOptimizations) { // Don't waste time with low future proposals.
proposalNumber = Math.max(proposalNumber, data.number);
}
if (betterNumber(data, bestProposal)) {
bestProposal = data;
if (claimCallback && useOptimizations) {
// Let the proposer know we're interested in the job if the proposer doesn't
// know who else to pick. Avoids needing to start multiple simultaneous proposals.
accepted.interested = ourId;
}
send1('promise', data.proposerId,
accepted.winner ? // data must include proposerId and number so that proposer catalogs results.
{number: accepted.number, winner: accepted.winner, proposerId: data.proposerId, proposalNumber: data.number} :
{proposerId: data.proposerId, proposalNumber: data.number});
} // FIXME nack?
});
receive('accept!', function (data) {
if (!betterNumber(bestProposal, data)) {
bestProposal = data;
if (useOptimizations) {
// The Paxos literature describe every acceptor sending 'accepted' to
// every proposer and learner. In our case, these are the same nodes that received
// the 'accept!' message, so we can send to just the originating proposer and invoke
// our own accepted handler directly.
// Note that this optimization cannot be used with Byzantine Paxos (which needs another
// multi-broadcast to detect lying and collusion).
subchannelHandlers[subchannelKey('accepted') + ourId].receiver(data);
send1('accepted', data.proposerId, data);
} else {
send('accepted', data);
}
}
});
// Paxos Learner behavior.
receive('accepted' + (useOptimizations ? ourId : ''), function (data) { // See note in 'accept!' regarding use of ourId here.
accepted = data;
if (acceptedId() === ourId) { // Note that we might not have been the proposer.
if (electionWatchdog) {
Script.clearTimeout(electionWatchdog);
electionWatchdog = null;
}
if (claimCallback) {
var callback = claimCallback;
claimCallback = undefined;
callback(key);
} else if (!releaseCallback) { // We won, but have been released and are no longer interested.
propose(); // Propose that someone else take the job.
}
}
});
receive('release', function (data) {
if (!betterNumber(accepted, data)) { // Unless our data is fresher...
debugFlow('baton:', ourId, 'handle release', data);
accepted.winner = null; // ... allow next proposer to have his way by making this explicitly null (not undefined).
if (recheckWatchdog) {
Script.clearInterval(recheckWatchdog);
recheckWatchdog = null;
}
}
});
function localRelease() {
var callback = releaseCallback, oldAccepted = accepted;
releaseCallback = undefined;
accepted = {number: oldAccepted.number, proposerId: oldAccepted.proposerId}; // A copy without winner assigned, preserving number.
debugFlow('baton: localRelease', key, !!callback);
if (!callback) { return; } // Already released, but we might still receive a stale message. That's ok.
callback(key); // Pass key so that clients may use the same handler for different batons.
return oldAccepted;
}
// Registers an intent to hold the baton:
// Calls onElection(key) once, if you are elected by the scripts
// to be the unique holder of the baton, which may be never.
// Calls onRelease(key) once, if you release the baton held by you,
// whether this is by you calling release(), or by loosing
// an election when you become disconnected.
// You may claim again at any time after the start of onRelease
// being called. Otherwise, you will not participate in further elections.
exports.claim = function claim(onElection, onRelease) {
debugFlow('baton:', ourId, 'claim');
if (claimCallback) {
print("Ignoring attempt to claim virtualBaton " + key + ", which is already waiting for claim.");
return;
}
if (releaseCallback) {
print("Ignoring attempt to claim virtualBaton " + key + ", which is somehow incorrect released, and that should not happen.");
return;
}
claimCallback = onElection;
releaseCallback = onRelease;
propose();
};
// Release the baton you hold, or just log that you are not holding it.
exports.release = function release(optionalReplacementOnRelease) {
debugFlow('baton:', ourId, 'release');
if (optionalReplacementOnRelease) { // E.g., maybe normal onRelease reclaims, but at shutdown you explicitly don't.
releaseCallback = optionalReplacementOnRelease;
}
if (acceptedId() !== ourId) {
print("Ignoring attempt to release virtualBaton " + key + ", which is not being held.");
return;
}
var released = localRelease();
if (released) {
send('release', released); // Let everyone know right away, including old number in case we overlap with reclaim.
}
if (!claimCallback) { // No claim set in release callback.
propose(); // We are the distinguished proposer, but we'll pick anyone else interested.
}
};
return exports;
};

354
examples/libraries/virtualBaton.39.js Normal file
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@ -0,0 +1,354 @@
"use strict";
/*jslint nomen: true, plusplus: true, vars: true */
/*global Messages, Script, MyAvatar, AvatarList, Entities, print */
// Created by Howard Stearns
// Copyright 2016 High Fidelity, Inc.
//
// Distributed under the Apache License, Version 2.0.
// See the accompanying file LICENSE or http://www.apache.org/licenses/LICENSE-2.0.html
//
// Allows cooperating scripts to pass a "virtual baton" between them,
// which is useful when part of a script should only be executed by
// the one participant that is holding this particular baton.
//
// A virtual baton is simply any string agreed upon by the scripts
// that use it. Only one script at a time can hold the baton, and it
// holds it until that script releases it, or the other scripts
// determine that the holding script is not responding. The script
// automatically determines who among claimants has the baton, if anyone,
// and holds an "election" if necessary.
//
// See entityScript/tribble.js as an example, and the functions
// virtualBaton(), claim(), release().
//
// Answers a new virtualBaton for the given parameters, of which 'key'
// is required.
function virtualBatonf(options) {
// Answer averages (number +/- variability). Avoids having everyone act in lockstep.
function randomize(number, variability) {
var allowedDeviation = number * variability;
return number - allowedDeviation + (Math.random() * 2 * allowedDeviation);
}
// Allow testing outside in a harness of High Fidelity.
var globals = options.globals || {},
messages = globals.Messages || Messages,
myAvatar = globals.MyAvatar || MyAvatar,
avatarList = globals.AvatarList || AvatarList,
entities = globals.Entities || Entities,
timers = globals.Script || Script,
log = globals.print || print;
var batonName = options.batonName, // The identify of the baton.
// instanceId is the identify of this particular copy of the script among all copies using the same batonName
// in the domain. For example, if you wanted only one entity among multiple entity scripts to hold the baton,
// you could specify virtualBaton({batonName: 'someBatonName', id: MyAvatar.sessionUUID + entityID}).
instanceId = options.instanceId || myAvatar.sessionUUID,
// virtualBaton() returns the exports object with properties. You can pass in an object to be side-effected.
exports = options.exports || {},
// Handy to set false if we believe the optimizations are wrong, or to use both values in a test harness.
useOptimizations = (options.useOptimizations === undefined) ? true : options.useOptimizations,
//
electionTimeout = options.electionTimeout || randomize(500, 0.2), // ms. If no winner in this time, hold a new election.
recheckInterval = options.recheckInterval || randomize(500, 0.2), // ms. Check that winners remain connected.
// If you supply your own instanceId, you can also supply a connectionTest to check that answers
// truthy iff the given id is still valid and connected, and is run at recheckInterval. You can use
// exports.validId (see below), and the default answers truthy if id is valid or a concatenation of two valid
// ids. (This handles the most common cases of instanceId being either (the default) MyAvatar.sessionUUID, an
// entityID, or the concatenation (in either order) of both.)
connectionTest = options.connectionTest || function connectionTest(id) {
var idLength = 38;
if (id.length === idLength) { return exports.validId(id); }
return (id.length === 2 * idLength) && exports.validId(id.slice(0, idLength)) && exports.validId(id.slice(idLength));
};
if (!batonName) {
throw new Error("A virtualBaton must specify a batonName.");
}
// Truthy if id exists as either a connected avatar or valid entity.
exports.validId = function validId(id) {
var avatar = avatarList.getAvatar(id);
if (avatar && (avatar.sessionUUID === id)) { return true; }
var properties = entities.getEntityProperties(id, ['type']);
return properties && properties.type;
};
// Various logging, controllable through options.
function debug() { // Display the arguments not just [Object object].
log.apply(null, [].map.call(arguments, JSON.stringify));
}
function debugFlow() {
if (options.debugFlow) { debug.apply(null, arguments); }
}
function debugSend(destination, operation, data) {
if (options.debugSend) { debug('baton:', batonName, instanceId, 's=>', destination, operation, data); }
}
function debugReceive(senderID, operation, data) { // senderID is client sessionUUID -- not necessarily instanceID!
if (options.debugReceive) { debug('baton:', batonName, senderID, '=>r', instanceId, operation, data); }
}
// Messages: Just synactic sugar for hooking things up to Messages system.
// We create separate subchannel strings for each operation within our general channelKey, instead of using
// a switch in the receiver.
var channelKey = "io.highfidelity.virtualBaton:" + batonName,
subchannelHandlers = {}, // Message channel string => {receiver, op}
subchannelKeys = {}; // operation => Message channel string
function subchannelKey(operation) { return channelKey + ':' + operation; }
function receive(operation, handler) { // Record a handler for an operation on our channelKey
var subKey = subchannelKey(operation);
subchannelHandlers[subKey] = {receiver: handler, op: operation};
subchannelKeys[operation] = subKey;
messages.subscribe(subKey);
}
function sendHelper(subchannel, data) {
var message = JSON.stringify(data);
messages.sendMessage(subchannel, message);
}
function send1(operation, destination, data) { // Send data for an operation to just one destination on our channelKey.
debugSend(destination, operation, data);
sendHelper(subchannelKey(operation) + destination, data);
}
function send(operation, data) { // Send data for an operation on our channelKey.
debugSend('-', operation, data);
sendHelper(subchannelKeys[operation], data);
}
function messageHandler(channel, messageString, senderID) {
var handler = subchannelHandlers[channel];
if (!handler) { return; }
var data = JSON.parse(messageString);
debugReceive(senderID, handler.op, data);
handler.receiver(data);
}
messages.messageReceived.connect(messageHandler);
var nPromises = 0, nAccepted = 0, electionWatchdog;
// It would be great if we had a way to know how many subscribers our channel has. Failing that...
var nNack = 0, previousNSubscribers = 0, lastGathering = 0, thisTimeout = electionTimeout;
function nSubscribers() { // Answer the number of subscribers - or zero to indicate that we have to wait.
// To find nQuorum, we need to know how many scripts are being run using this batonName, which isn't
// the same as the number of clients!
//
// If we overestimate by too much, we may fail to reach consensus, which triggers a new
// election proposal, so we take the number of acceptors to be the max(nPromises, nAccepted)
// + nNack reported in the previous round.
//
// If we understimate by too much, there can be different pockets on the Internet that each
// believe they have agreement on different holders of the baton, which is precisely what
// the virtualBaton is supposed to avoid. Therefore we need to allow 'nack' gather stragglers.
var now = Date.now(), elapsed = now - lastGathering;
if (elapsed >= thisTimeout) {
previousNSubscribers = Math.max(nPromises, nAccepted) + nNack;
lastGathering = now;
} // ...otherwise we use the previous value unchanged.
// On startup, we do one proposal that we cannot possibly win, so that we'll
// lock things up for timeout to gather the number of responses.
if (!previousNSubscribers) {
var LARGE_INTEGER = Number.MAX_SAFE_INTEGER || (-1 >>> 1); // QT doesn't define the ECMA constant. Max int will do for our purposes.
previousNSubscribers = LARGE_INTEGER;
}
return previousNSubscribers;
}
// MAIN ALGORITHM
//
// Internally, this uses the Paxos algorith to hold elections.
// Alternatively, we could have the message server pick and maintain a winner, but it would
// still have to deal with the same issues of verification in the presence of lost/delayed/reordered messages.
// Paxos is known to be optimal under these circumstances, except that its best to have a dedicated proposer
// (such as the server).
function betterNumber(number, best) {
return (number.number || 0) > best.number;
}
// Paxos Proposer behavior
var proposalNumber = 0,
nQuorum = 0,
bestPromise = {number: 0},
claimCallback,
releaseCallback;
function propose() { // Make a new proposal, so that we learn/update the proposalNumber and winner.
// Even though we send back a 'nack' if the proposal is obsolete, with net work errors
// there's no way to know for certain that we've failed. The electionWatchdog will try a new
// proposal if we have not been accepted by a quorum after election Timeout.
if (electionWatchdog) {
// If we had a means of determining nSubscribers other than by counting, we could just
// timers.clearTimeout(electionWatchdog) and not return.
return;
}
thisTimeout = randomize(electionTimeout, 0.5); // for accurate nSubcribers counting.
electionWatchdog = timers.setTimeout(function () {
electionWatchdog = null;
propose();
}, thisTimeout);
var nAcceptors = nSubscribers();
nQuorum = Math.floor(nAcceptors / 2) + 1;
proposalNumber = Math.max(proposalNumber, bestPromise.number) + 1;
debugFlow('baton:', batonName, instanceId, 'propose', proposalNumber,
'claim:', !!claimCallback, 'nAcceptors:', nAcceptors, nPromises, nAccepted, nNack);
nPromises = nAccepted = nNack = 0;
send('prepare!', {number: proposalNumber, proposerId: instanceId});
}
// We create a distinguished promise subchannel for our id, because promises need only be sent to the proposer.
receive('promise' + instanceId, function (data) {
if (betterNumber(data, bestPromise)) {
bestPromise = data;
}
if ((data.proposalNumber === proposalNumber) && (++nPromises >= nQuorum)) { // Note check for not being a previous round
var answer = {number: data.proposalNumber, proposerId: data.proposerId, winner: bestPromise.winner}; // Not data.number.
if (!answer.winner || (answer.winner === instanceId)) { // We get to pick.
answer.winner = claimCallback ? instanceId : null;
}
send('accept!', answer);
}
});
receive('nack' + instanceId, function (data) { // An acceptor reports more recent data...
if (data.proposalNumber === proposalNumber) {
nNack++; // For updating nQuorum.
// IWBNI if we started our next proposal now (here, in a setTimeout, but we need a decent nNack count.
// Lets save that optimization for another day...
}
});
// Paxos Acceptor behavior
var bestProposal = {number: 0}, accepted = {};
function acceptedId() { return accepted && accepted.winner; }
receive('prepare!', function (data) {
var response = {proposalNumber: data.number, proposerId: data.proposerId};
if (betterNumber(data, bestProposal)) {
bestProposal = data;
if (accepted.winner) {
response.number = accepted.number;
response.winner = accepted.winner;
}
send1('promise', data.proposerId, response);
} else {
send1('nack', data.proposerId, response);
}
});
receive('accept!', function (data) {
if (!betterNumber(bestProposal, data)) {
bestProposal = accepted = data; // Update both with current data. Might have missed the proposal earlier.
if (useOptimizations) {
// The Paxos literature describe every acceptor sending 'accepted' to
// every proposer and learner. In our case, these are the same nodes that received
// the 'accept!' message, so we can send to just the originating proposer and invoke
// our own accepted handler directly.
// Note that this optimization cannot be used with Byzantine Paxos (which needs another
// multi-broadcast to detect lying and collusion).
debugSend('/', 'accepted', data);
debugReceive(instanceId, 'accepted', data); // direct on next line, which doesn't get logging.
subchannelHandlers[subchannelKey('accepted') + instanceId].receiver(data);
if (data.proposerId !== instanceId) { // i.e., we didn't already do it directly on the line above.
send1('accepted', data.proposerId, data);
}
} else {
send('accepted', data);
}
} else {
send1('nack', data.proposerId, {proposalNumber: data.number});
}
});
// Paxos Learner behavior.
function localRelease() {
var callback = releaseCallback;
debugFlow('baton:', batonName, 'localRelease', 'callback:', !!releaseCallback);
if (!releaseCallback) { return; } // Already released, but we might still receive a stale message. That's ok.
releaseCallback = undefined;
callback(batonName); // Pass batonName so that clients may use the same handler for different batons.
}
receive('accepted' + (useOptimizations ? instanceId : ''), function (data) { // See note in 'accept!' regarding use of instanceId here.
if (betterNumber(accepted, data)) { // Especially when !useOptimizations, we can receive other acceptances late.
return;
}
var oldAccepted = accepted;
debugFlow('baton:', batonName, instanceId, 'accepted', data.number, data.winner);
accepted = data;
// If we are proposer, make sure we get a quorum of acceptances.
if ((data.proposerId === instanceId) && (data.number === proposalNumber) && (++nAccepted >= nQuorum)) {
if (electionWatchdog) {
timers.clearTimeout(electionWatchdog);
electionWatchdog = null;
}
}
// If we are the winner -- regardless of whether we were the proposer.
if (acceptedId() === instanceId) {
if (claimCallback) {
var callback = claimCallback;
claimCallback = undefined;
callback(batonName);
} else if (!releaseCallback) { // We won, but have been released and are no longer interested.
// Propose that someone else take the job.
timers.setTimeout(propose, 0); // Asynchronous to queue message handling if some are synchronous and others not.
}
} else if (releaseCallback && (oldAccepted.winner === instanceId)) { // We've been released by someone else!
localRelease(); // This can happen if enough people thought we'd disconnected.
}
});
// Registers an intent to hold the baton:
// Calls onElection(batonName) once, if you are elected by the scripts
// to be the unique holder of the baton, which may be never.
// Calls onRelease(batonName) once, if you release the baton held by you,
// whether this is by you calling release(), or by loosing
// an election when you become disconnected.
// You may claim again at any time after the start of onRelease
// being called. Otherwise, you will not participate in further elections.
exports.claim = function claim(onElection, onRelease) {
debugFlow('baton:', batonName, instanceId, 'claim');
if (claimCallback) {
log("Ignoring attempt to claim virtualBaton " + batonName + ", which is already waiting for claim.");
return;
}
if (releaseCallback) {
log("Ignoring attempt to claim virtualBaton " + batonName + ", which is somehow incorrect released, and that should not happen.");
return;
}
claimCallback = onElection;
releaseCallback = onRelease;
propose();
return exports; // Allows chaining. e.g., var baton = virtualBaton({batonName: 'foo'}.claim(onClaim, onRelease);
};
// Release the baton you hold, or just log that you are not holding it.
exports.release = function release(optionalReplacementOnRelease) {
debugFlow('baton:', batonName, instanceId, 'release');
if (optionalReplacementOnRelease) { // E.g., maybe normal onRelease reclaims, but at shutdown you explicitly don't.
releaseCallback = optionalReplacementOnRelease;
}
if (acceptedId() !== instanceId) {
log("Ignoring attempt to release virtualBaton " + batonName + ", which is not being held.");
return;
}
localRelease();
if (!claimCallback) { // No claim set in release callback.
propose(); // We are the distinguished proposer, but we'll pick anyone else interested, else set it to null.
}
return exports;
};
exports.recheckWatchdog = timers.setInterval(function recheck() {
var holder = acceptedId(); // If we're waiting and we notice the holder is gone, ...
if (holder && claimCallback && !electionWatchdog && !connectionTest(holder)) {
propose(); // ... propose an election.
}
}, recheckInterval);
exports.unload = function unload() { // Disconnect from everything.
messages.messageReceived.disconnect(messageHandler);
timers.clearInterval(exports.recheckWatchdog);
if (electionWatchdog) { timers.clearTimeout(electionWatchdog); }
electionWatchdog = claimCallback = releaseCallback = null;
Object.keys(subchannelHandlers).forEach(messages.unsubscribe);
debugFlow('baton:', batonName, instanceId, 'unload');
return exports;
};
// Gather nAcceptors by making two proposals with some gathering time, even without a claim.
propose();
return exports;
}
if (typeof module !== 'undefined') {
module.exports = virtualBatonf;
} else {
virtualBaton = virtualBatonf;
}