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This commit is contained in:
Howard Stearns 2016-02-03 11:10:04 -08:00
parent 59f1cdfc18
commit 055de61ec6
2 changed files with 48 additions and 32 deletions
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76
examples/libraries/virtualBaton.27.js → examples/libraries/virtualBaton.29.js
View file

@ -26,18 +26,21 @@
// Answers a new virtualBaton for the given parameters, of which 'key' // Answers a new virtualBaton for the given parameters, of which 'key'
// is required. // is required.
virtualBaton = function virtualBaton(options) { virtualBaton = function virtualBaton(options) {
var key = options.key, var key = options.key,
channel = "io.highfidelity.virtualBaton:" + key, channel = "io.highfidelity.virtualBaton:" + key,
exports = options.exports || {}, exports = options.exports || {},
claimCallback, claimCallback,
releaseCallback, releaseCallback,
// paxos proposer state // paxos proposer state
nPromises = 0, nPromises = 0,
proposalNumber = 0,
nQuorum, nQuorum,
mostRecentInterested, mostRecentInterested,
bestPromise = {number: 0}, bestPromise = {number: 0},
electionTimeout = options.electionTimeout || 1000, // ms. If no winner in this time, hold a new election electionTimeout = options.electionTimeout || 1000, // ms. If no winner in this time, hold a new election. FIXME randomize
electionWatchdog, electionWatchdog,
recheckInterval = options.recheckInterval || 1000, // ms. Check that winners remain connected. FIXME rnadomize
recheckWatchdog,
// paxos acceptor state // paxos acceptor state
bestProposal = {number: 0}, bestProposal = {number: 0},
accepted = {}; accepted = {};
@ -45,23 +48,26 @@ virtualBaton = function virtualBaton(options) {
throw new Error("A VirtualBaton must specify a key."); throw new Error("A VirtualBaton must specify a key.");
} }
function debug() { function debug() {
print.apply(null, [].map.call(arguments, JSON.stringify)); print.apply(print, [].map.call(arguments, JSON.stringify)); // fixme no console
}
function debugFlow() {
if (options.debugFlow) { debug.apply(null, arguments); }
} }
function send(operation, data) { function send(operation, data) {
debug('baton: send', operation, data); if (options.debugSend) { debug('baton:', MyAvatar.sessionUUID, '=>', '-', operation, data); }
var message = JSON.stringify({op: operation, data: data}); var message = JSON.stringify({op: operation, data: data});
Messages.sendMessage(channel, message); Messages.sendMessage(channel, message);
} }
function doRelease() { function localRelease() {
var callback = releaseCallback, oldAccepted = accepted; var callback = releaseCallback, oldAccepted = accepted;
releaseCallback = undefined; releaseCallback = undefined;
accepted = {number: oldAccepted.number, proposerId: oldAccepted.proposerId}; accepted = {number: oldAccepted.number, proposerId: oldAccepted.proposerId}; // A copy without winner assigned, preserving number.
debug('baton: doRelease', key, callback); debugFlow('baton: localRelease', key, !!callback);
if (!callback) { return; } // Already released, but we might still receive a stale message. That's ok. if (!callback) { return; } // Already released, but we might still receive a stale message. That's ok.
Messages.messageReceived.disconnect(messageHandler); //Messages.messageReceived.disconnect(messageHandler);
Messages.unsubscribe(channel); // Messages currently allow publishing without subscription. //Messages.unsubscribe(channel); // Messages currently allow publishing without subscription.
send('release', oldAccepted); // This order is less crufty.
callback(key); // Pass key so that clients may use the same handler for different batons. callback(key); // Pass key so that clients may use the same handler for different batons.
return oldAccepted;
} }
// Internally, this uses the Paxos algorith to hold elections. // Internally, this uses the Paxos algorith to hold elections.
@ -69,38 +75,37 @@ virtualBaton = function virtualBaton(options) {
// still have to deal with the same issues of verification in the presence of lost/delayed/reordered messages. // 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 // Paxos is known to be optimal under these circumstances, except that its best to have a dedicated proposer
// (such as the server). // (such as the server).
function acceptedId() { return accepted && accepted.winner; } // fixme doesn't need to be so fancy any more? function acceptedId() { return accepted && accepted.winner; }
// Paxos makes several tests of one "proposal number" versus another, assuming // Paxos makes several tests of one "proposal number" versus another, assuming
// that better proposals from the same proposer have a higher number, // that better proposals from the same proposer have a higher number,
// and different proposers use a different set of numbers. We achieve that // and different proposers use a different set of numbers. We achieve that
// by dividing the "number" into two parts, and integer and a proposerId, // by dividing the "number" into two parts, and integer and a proposerId,
// which keeps the combined number unique and yet still strictly ordered. // which keeps the combined number unique and yet still strictly ordered.
function betterNumber(number, best) { function betterNumber(number, best) {
debug('baton: betterNumber', number, best); // FIXME restore debug('baton: betterNumber', number, best);
//FIXME return ((number.number || 0) > best.number) && (!best.proposerId || (number.proposerId >= best.proposerId)); //FIXME return ((number.number || 0) > best.number) && (!best.proposerId || (number.proposerId >= best.proposerId));
return (number.number || 0) > best.number; return (number.number || 0) > best.number;
} }
function propose(claim) { function propose() {
debug('baton: propose', claim); debugFlow('baton:', MyAvatar.sessionUUID, 'propose', !!claimCallback);
if (electionWatchdog) { Script.clearTimeout(electionWatchdog); } if (electionWatchdog) { Script.clearTimeout(electionWatchdog); }
if (!claimCallback) { return; } // We're not participating. if (!claimCallback) { return; } // We're not participating.
nPromises = 0; 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! nQuorum = Math.floor(AvatarList.getAvatarIdentifiers().length / 2) + 1; // N.B.: ASSUMES EVERY USER IS RUNNING THE SCRIPT!
bestPromise = {number: ++bestPromise.number, proposerId: MyAvatar.sessionUUID, winner: claim}; send('prepare!', {number: ++proposalNumber, proposerId: MyAvatar.sessionUUID});
send('prepare!', bestPromise); electionWatchdog = Script.setTimeout(propose, electionTimeout);
function reclaim() { propose(claim); }
electionWatchdog = Script.setTimeout(reclaim, electionTimeout);
} }
function messageHandler(messageChannel, messageString, senderID) { function messageHandler(messageChannel, messageString, senderID) {
if (messageChannel !== channel) { return; } if (messageChannel !== channel) { return; }
var message = JSON.parse(messageString), data = message.data; var message = JSON.parse(messageString), data = message.data;
debug('baton: received from', senderID, message.op, data); if (options.debugReceive) { debug('baton:', senderID, '=>', MyAvatar.sessionUUID, message.op, data); }
switch (message.op) { switch (message.op) {
case 'prepare!': case 'prepare!':
// Optimization: Don't waste time with low future proposals. // Optimization: Don't waste time with low future proposals.
// Does not remove the need for betterNumber() to consider proposerId, because // Does not remove the need for betterNumber() to consider proposerId, because
// participants might not receive this prepare! message before their next proposal. // participants might not receive this prepare! message before their next proposal.
//FIXME bestPromise.number = Math.max(bestPromise.number, data.number); proposalNumber = Math.max(proposalNumber, data.number);
if (betterNumber(data, bestProposal)) { if (betterNumber(data, bestProposal)) {
bestProposal = data; bestProposal = data;
@ -111,7 +116,7 @@ virtualBaton = function virtualBaton(options) {
} }
send('promise', accepted.winner ? // data must include proposerId so that proposer catalogs results. send('promise', accepted.winner ? // data must include proposerId so that proposer catalogs results.
{number: accepted.number, proposerId: data.proposerId, winner: accepted.winner} : {number: accepted.number, proposerId: data.proposerId, winner: accepted.winner} :
{proposerId: data.proposerId}); {number: data.number, proposerId: data.proposerId});
} // FIXME nack? } // FIXME nack?
break; break;
case 'promise': case 'promise':
@ -130,11 +135,12 @@ virtualBaton = function virtualBaton(options) {
case 'accept!': case 'accept!':
if (!betterNumber(bestProposal, data)) { if (!betterNumber(bestProposal, data)) {
accepted = data; accepted = data;
send('accepted', accepted); //send('accepted', accepted); // With the collapsed roles here, do we need this message? Maybe just go to 'accepted' case here?
messageHandler(messageChannel, JSON.stringify({op: 'accepted', data: accepted}), senderID);
} }
// FIXME: start interval (with a little random offset?) that claims if winner is ever not in AvatarList and we still claimCallback
break; break;
case 'accepted': case 'accepted':
if (betterNumber(accepted, data)) { return; }
accepted = data; accepted = data;
if (acceptedId() === MyAvatar.sessionUUID) { // Note that we might not have been the proposer. if (acceptedId() === MyAvatar.sessionUUID) { // Note that we might not have been the proposer.
if (electionWatchdog) { if (electionWatchdog) {
@ -145,7 +151,7 @@ virtualBaton = function virtualBaton(options) {
var callback = claimCallback; var callback = claimCallback;
claimCallback = undefined; claimCallback = undefined;
callback(key); callback(key);
} else { // We won, but are no longer interested. } else if (!releaseCallback) { // We won, but have been released and are no longer interested.
propose(); // Propose that someone else take the job. propose(); // Propose that someone else take the job.
} }
} }
@ -153,12 +159,19 @@ virtualBaton = function virtualBaton(options) {
case 'release': case 'release':
if (!betterNumber(accepted, data)) { // Unless our data is fresher... if (!betterNumber(accepted, data)) { // Unless our data is fresher...
accepted.winner = undefined; // ... allow next proposer to have his way. accepted.winner = undefined; // ... allow next proposer to have his way.
if (recheckWatchdog) {
Script.clearInterval(recheckWatchdog);
recheckWatchdog = null;
}
} }
break; break;
default: default:
print("Unrecognized virtualBaton message:", message); print("Unrecognized virtualBaton message:", message);
} }
} }
Messages.messageReceived.connect(messageHandler); // FIXME MUST BE DONE. quorum will be wrong if no one claims and we only subscrbe with claims
Messages.subscribe(channel); // FIXME
// Registers an intent to hold the baton: // Registers an intent to hold the baton:
// Calls onElection(key) once, if you are elected by the scripts // Calls onElection(key) once, if you are elected by the scripts
// to be the unique holder of the baton, which may be never. // to be the unique holder of the baton, which may be never.
@ -168,7 +181,7 @@ virtualBaton = function virtualBaton(options) {
// You may claim again at any time after the start of onRelease // You may claim again at any time after the start of onRelease
// being called. Otherwise, you will not participate in further elections. // being called. Otherwise, you will not participate in further elections.
exports.claim = function claim(onElection, onRelease) { exports.claim = function claim(onElection, onRelease) {
debug('baton: claim'); debugFlow('baton:', MyAvatar.sessionUUID, 'claim');
if (claimCallback) { if (claimCallback) {
print("Ignoring attempt to claim virtualBaton " + key + ", which is already waiting for claim."); print("Ignoring attempt to claim virtualBaton " + key + ", which is already waiting for claim.");
return; return;
@ -179,14 +192,14 @@ virtualBaton = function virtualBaton(options) {
} }
claimCallback = onElection; claimCallback = onElection;
releaseCallback = onRelease; releaseCallback = onRelease;
Messages.messageReceived.connect(messageHandler); //Messages.messageReceived.connect(messageHandler);
Messages.subscribe(channel); //Messages.subscribe(channel);
propose(MyAvatar.sessionUUID); propose();
}; };
// Release the baton you hold, or just log that you are not holding it. // Release the baton you hold, or just log that you are not holding it.
exports.release = function release(optionalReplacementOnRelease) { exports.release = function release(optionalReplacementOnRelease) {
debug('baton: release'); debugFlow('baton:', MyAvatar.sessionUUID, 'release');
if (optionalReplacementOnRelease) { // E.g., maybe normal onRelease reclaims, but at shutdown you explicitly don't. if (optionalReplacementOnRelease) { // E.g., maybe normal onRelease reclaims, but at shutdown you explicitly don't.
releaseCallback = optionalReplacementOnRelease; releaseCallback = optionalReplacementOnRelease;
} }
@ -194,7 +207,10 @@ virtualBaton = function virtualBaton(options) {
print("Ignoring attempt to release virtualBaton " + key + ", which is not being held."); print("Ignoring attempt to release virtualBaton " + key + ", which is not being held.");
return; return;
} }
doRelease(); 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. if (!claimCallback) { // No claim set in release callback.
propose(); // We are the distinguished proposer, but we'll pick anyone else interested. propose(); // We are the distinguished proposer, but we'll pick anyone else interested.
} }

4
examples/tests/testBaton.js
View file

@ -12,9 +12,9 @@ var Vec3, Quat, MyAvatar, Entities, Camera, Script, print;
// All participants should run the test script. // All participants should run the test script.
Script.include("../libraries/virtualBaton.27.js"); Script.include("../libraries/virtualBaton.29.js");
var TICKER_INTERVAL = 1000; // ms var TICKER_INTERVAL = 1000; // ms
var baton = virtualBaton({key: 'io.highfidelity.testBaton'}); var baton = virtualBaton({key: 'io.highfidelity.testBaton', debugSend: true, debugFlow: true, debugReceive: true});
var ticker, countDown; var ticker, countDown;
// Tick every TICKER_INTERVAL. // Tick every TICKER_INTERVAL.