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Skip useless tasks in the worker to improve fast scrolling with scanned books (bug 1866296) #17403

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Skip useless tasks in the worker to improve fast scrolling with scanned books (bug 1866296) #17403

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167 changes: 110 additions & 57 deletions src/shared/message_handler.js
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Original file line number Diff line number Diff line change
Expand Up @@ -70,6 +70,14 @@ function wrapReason(reason) {
}

class MessageHandler {
#cancelledStreamIds = new Set();

#executorRunning = false;

#isPostponed = false;

#queue = [];

constructor(sourceName, targetName, comObj) {
this.sourceName = sourceName;
this.targetName = targetName;
Expand All @@ -81,71 +89,116 @@ class MessageHandler {
this.callbackCapabilities = Object.create(null);
this.actionHandler = Object.create(null);

this._onComObjOnMessage = event => {
const data = event.data;
if (data.targetName !== this.sourceName) {
return;
}
if (data.stream) {
this.#processStreamMessage(data);
return;
}
if (data.callback) {
const callbackId = data.callbackId;
const capability = this.callbackCapabilities[callbackId];
if (!capability) {
throw new Error(`Cannot resolve callback ${callbackId}`);
this._onComObjOnMessage = ({ data }) => {
if (data.targetName === this.sourceName) {
// The meesages in the worker queue are processed with a
// higher priority than the tasks in the event queue.
// So, postponing the task execution, will ensure that the message
// queue is drained.
// If at some point we've a cancelled task (e.g. GetOperatorList),
// we're able to skip the task execution with the same streamId.
this.#queue.push(data);
this.#isPostponed ||= data.action === "GetOperatorList";
if (data.stream === StreamKind.CANCEL) {
this.#cancelledStreamIds.add(data.streamId);
}
delete this.callbackCapabilities[callbackId];

if (data.callback === CallbackKind.DATA) {
capability.resolve(data.data);
} else if (data.callback === CallbackKind.ERROR) {
capability.reject(wrapReason(data.reason));
} else {
throw new Error("Unexpected callback case");
if (!this.#executorRunning) {
this.#executorRunning = true;
this.#postponeExecution();
}
return;
}
const action = this.actionHandler[data.action];
if (!action) {
throw new Error(`Unknown action from worker: ${data.action}`);
};
comObj.addEventListener("message", this._onComObjOnMessage);
}

#postponeExecution() {
if (this.#isPostponed) {
setTimeout(this.#executor.bind(this), 0);
} else {
this.#executor();
}
}

#executor() {
if (this.#queue.length === 0) {
this.#cancelledStreamIds.clear();
this.#executorRunning = false;
return;
}

const data = this.#queue.shift();
const { stream, streamId } = data;

if (stream) {
if (
stream === StreamKind.CANCEL ||
!this.#cancelledStreamIds.has(streamId)
) {
this.#processStreamMessage(data);
}
if (data.callbackId) {
const cbSourceName = this.sourceName;
const cbTargetName = data.sourceName;
this.#postponeExecution();
return;
}

new Promise(function (resolve) {
resolve(action(data.data));
}).then(
function (result) {
comObj.postMessage({
sourceName: cbSourceName,
targetName: cbTargetName,
callback: CallbackKind.DATA,
callbackId: data.callbackId,
data: result,
});
},
function (reason) {
comObj.postMessage({
sourceName: cbSourceName,
targetName: cbTargetName,
callback: CallbackKind.ERROR,
callbackId: data.callbackId,
reason: wrapReason(reason),
});
}
);
return;
if (streamId && this.#cancelledStreamIds.has(streamId)) {
this.#postponeExecution();
return;
}

if (data.callback) {
const callbackId = data.callbackId;
const capability = this.callbackCapabilities[callbackId];
if (!capability) {
throw new Error(`Cannot resolve callback ${callbackId}`);
}
if (data.streamId) {
this.#createStreamSink(data);
return;
delete this.callbackCapabilities[callbackId];

if (data.callback === CallbackKind.DATA) {
capability.resolve(data.data);
} else if (data.callback === CallbackKind.ERROR) {
capability.reject(wrapReason(data.reason));
} else {
throw new Error("Unexpected callback case");
}
this.#postponeExecution();
return;
}
const action = this.actionHandler[data.action];
if (!action) {
throw new Error(`Unknown action from worker: ${data.action}`);
}
if (data.callbackId) {
const cbSourceName = this.sourceName;
const cbTargetName = data.sourceName;

new Promise(function (resolve) {
resolve(action(data.data));
}).then(
result => {
this.comObj.postMessage({
sourceName: cbSourceName,
targetName: cbTargetName,
callback: CallbackKind.DATA,
callbackId: data.callbackId,
data: result,
});
},
reason => {
this.comObj.postMessage({
sourceName: cbSourceName,
targetName: cbTargetName,
callback: CallbackKind.ERROR,
callbackId: data.callbackId,
reason: wrapReason(reason),
});
}
);
} else if (data.streamId) {
this.#createStreamSink(data);
} else {
action(data.data);
};
comObj.addEventListener("message", this._onComObjOnMessage);
}
this.#postponeExecution();
}

on(actionName, handler) {
Expand Down