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Use versioning to make sure that state positions can always be resolv…
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…ed across cell partitions
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@jondubois
jondubois committed Jan 2, 2017
1 parent e1ccd37 commit f3c904b
Showing 1 changed file with 47 additions and 22 deletions.
69 changes: 47 additions & 22 deletions worker.js
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Original file line number Diff line number Diff line change
Expand Up @@ -79,6 +79,7 @@ var privateProps = {
groupWith: true,
ungroupFrom: true,
group: true,
version: true,
external: true
};

Expand Down Expand Up @@ -289,6 +290,22 @@ module.exports.run = function (worker) {
return groupA.leader.id <= groupB.leader.id;
}

/*
Groups are not passed around between cells/processes. Their purpose is to allow
states to seamlessly interact with one another across cell boundaries.
When one state affects another state across cell boundaries (e.g. one player
pushing another player into a different cell), there is a slight delay for
the position information to be shared across processes/CPU cores; as a
result of this, the states may not show up in the exact same position in both cells.
When two cells report slightly different positions for the same set of
states, it may cause overlapping and flickering on the front end since the
front end doesn't know which data to trust.
A group allows two cells to agree on which cell is responsible for broadcasting the
position of states that are within the group by considering the group's average position
instead of looking at the position of member states individually.
*/
function getStateGroups() {
var groupMap = {};
Object.keys(cellData).forEach(function (cellIndex) {
Expand Down Expand Up @@ -512,6 +529,7 @@ module.exports.run = function (worker) {
var transformedStateList = [];

cellIndexList.forEach(function (cellIndex) {
cellIndex = Number(cellIndex);
prepareStatesForProcessing(cellIndex);
cellControllers[cellIndex].run(cellData[cellIndex]);
prepareGroupStatesBeforeDispatching(cellIndex);
Expand All @@ -523,6 +541,7 @@ module.exports.run = function (worker) {
var groupMap = getStateGroups();

cellIndexList.forEach(function (cellIndex) {
cellIndex = Number(cellIndex);
var currentCellData = cellData[cellIndex];
Object.keys(currentCellData).forEach(function (type) {
if (!cellSpecialIntervalTypes[type]) {
Expand All @@ -544,6 +563,7 @@ module.exports.run = function (worker) {
// Deletions are processed as part of WORLD_UPDATE_INTERVAL even if
// that type has its own special interval.
Object.keys(cellPendingDeletes).forEach(function (cellIndex) {
cellIndex = Number(cellIndex);
var currentCellDeletes = cellPendingDeletes[cellIndex];
Object.keys(currentCellDeletes).forEach(function (type) {
var cellDeleteStates = currentCellDeletes[type] || {};
Expand All @@ -559,6 +579,7 @@ module.exports.run = function (worker) {
});

Object.keys(groupMap).forEach(function (cellIndex) {
cellIndex = Number(cellIndex);
var currentGroupMap = groupMap[cellIndex];
Object.keys(currentGroupMap).forEach(function (groupId) {
var group = currentGroupMap[groupId];
Expand Down Expand Up @@ -607,6 +628,7 @@ module.exports.run = function (worker) {
// other cells' boundaries and prepare for transition to other cells.
// This logic is quite complex so be careful when changing any code here.
function dispatchProcessedData(cellIndex) {
var now = Date.now();
var currentCellData = cellData[cellIndex];
var workerStateRefList = {};
var statesForNearbyCells = {};
Expand All @@ -616,6 +638,17 @@ module.exports.run = function (worker) {
var swid = state.swid;
var type = state.type;

if (!state.external) {
if (state.version) {
state.version++;
if (state.version >= Number.MAX_SAFE_INTEGER) {
state.version = 0;
}
} else {
state.version = 1;
}
}

// The target cell id
state.tcid = channelGrid.getCellIndex(state);

Expand All @@ -633,17 +666,7 @@ module.exports.run = function (worker) {
}
// No need for the cell to send states to itself.
if (nearbyCellIndex != cellIndex) {
// If the state is transitioning to a new owner cell, then
// we want to be extra careful and make sure that it is not
// already in the middle of a transition (synching).
if (nearbyCellIndex == state.tcid) {
if (!state.synching) {
state.synching = 1;
statesForNearbyCells[nearbyCellIndex].push(state);
}
} else {
statesForNearbyCells[nearbyCellIndex].push(state);
}
statesForNearbyCells[nearbyCellIndex].push(state);
}
});

Expand All @@ -665,7 +688,7 @@ module.exports.run = function (worker) {
}
}

state.processed = Date.now();
state.processed = now;

if (state.delete) {
if (!cellPendingDeletes[cellIndex][type]) {
Expand All @@ -674,7 +697,7 @@ module.exports.run = function (worker) {
cellPendingDeletes[cellIndex][type][id] = state;
delete currentCellData[type][id];
}
if (Date.now() - state.processed > WORLD_STALE_TIMEOUT) {
if (now - state.processed > WORLD_STALE_TIMEOUT) {
delete currentCellData[type][id];
}
});
Expand All @@ -697,7 +720,9 @@ module.exports.run = function (worker) {
var type = state.type;
var id = state.id;

if (currentCellData[type] && currentCellData[type][id]) {
if (!currentCellData[type] || !currentCellData[type][id] ||
state.version > currentCellData[type][id].version || !state.version) {

state.processed = Date.now();
updateStateExternalTag(state, cellIndex);
currentCellData[type][id] = state;
Expand All @@ -717,17 +742,16 @@ module.exports.run = function (worker) {
stateList.forEach(function (state) {
var type = state.type;
var id = state.id;
delete state.synching;
state.processed = Date.now();

if (!currentCellData[type]) {
currentCellData[type] = {};
}
var existingState = currentCellData[type][id];

// Do not overwrite a state which is in the middle of
// being synchronized with a different cell.
if (!existingState || !existingState.synching) {
if (!existingState || state.version > existingState.version || !state.version) {
// Do not overwrite a state which is in the middle of
// being synchronized with a different cell.
if (state.tcid == cellIndex) {
// Previous cell id.
state.pcid = state.ccid;
Expand All @@ -739,12 +763,10 @@ module.exports.run = function (worker) {
// This is just external state for us to track but not
// a complete transition, the state will still be managed by
// a different cell.
if (!existingState || existingState.external) {
currentCellData[type][id] = state;
}
currentCellData[type][id] = state;
}
updateStateExternalTag(state, cellIndex);
}
updateStateExternalTag(state, cellIndex);
});

newlyAcceptedStates.forEach(function (state) {
Expand Down Expand Up @@ -782,8 +804,11 @@ module.exports.run = function (worker) {
// If we have x and y properties, then we know that
// this is a full state already (probably created directly inside the cell).
state = stateRef;
} else {
throw new Error('Received an invalid state reference');
}
state.ccid = cellIndex;
state.version = 1;
currentCellData[type][id] = state;
}
var cachedState = currentCellData[type][id];
Expand Down

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