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events: use bitset in listener to save memory #43700

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events: use bitset in listener to save memory #43700

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194af02
listener: use bitset to save memory
mabaasit Jul 6, 2022
e344b4b
events: code styles and use bit shifts
mabaasit Jul 6, 2022
73a689e
Update lib/internal/event_target.js
mabaasit Jul 8, 2022
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52 changes: 46 additions & 6 deletions lib/internal/event_target.js
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Original file line number Diff line number Diff line change
Expand Up @@ -347,6 +347,13 @@ function weakListeners() {
return { registry: weakListenersState, map: objectToWeakListenerMap };
}

const FLAG_ONCE = 1;
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const FLAG_CAPTURE = 2;
const FLAG_PASSIVE = 4;
const FLAG_NODE_STYLE = 8;
const FLAG_WEAK = 16;
const FLAG_REMOVED = 32;

// The listeners for an EventTarget are maintained as a linked list.
// Unfortunately, the way EventTarget is defined, listeners are accounted
// using the tuple [handler,capture], and even if we don't actually make
Expand All @@ -362,13 +369,21 @@ class Listener {
previous.next = this;
this.previous = previous;
this.listener = listener;
// TODO(benjamingr) these 4 can be 'flags' to save 3 slots
this.once = once;
this.capture = capture;
this.passive = passive;
this.isNodeStyleListener = isNodeStyleListener;

let flags = 0b0;
if (once)
flags |= FLAG_ONCE;
if (capture)
flags |= FLAG_CAPTURE;
if (passive)
flags |= FLAG_PASSIVE;
if (isNodeStyleListener)
flags |= FLAG_NODE_STYLE;
if (Boolean(weak))
flags |= FLAG_WEAK;
this.flags = flags;
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@aduh95 aduh95 Jul 6, 2022 •
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Suggested change
let flags = 0b0;
if (once)
flags |= FLAG_ONCE;
if (capture)
flags |= FLAG_CAPTURE;
if (passive)
flags |= FLAG_PASSIVE;
if (isNodeStyleListener)
flags |= FLAG_NODE_STYLE;
if (Boolean(weak))
flags |= FLAG_WEAK;
this.flags = flags;
this.flags =
(once && FLAG_ONCE) |
(capture && FLAG_CAPTURE) |
(isNodeStyleListener && FLAG_NODE_STYLE) |
(Boolean(weak) && FLAG_WEAK);

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@benjamingr benjamingr Jul 6, 2022 •
edited
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This is a bit too clever for my taste because of the reliance on how && uses the righthand side for the value. (Just personal taste)

Also, why is weak wrapped (before and after) in a conversion?


this.removed = false;
this.weak = Boolean(weak); // Don't retain the object

if (this.weak) {
this.callback = new SafeWeakRef(listener);
Expand All @@ -388,6 +403,31 @@ class Listener {
}
}

get once() {
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Since this is just a listener and is internal these can probably just be static methods - though I am fine with landing this and iterating :)

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@benjamingr Just curious, what would be the advantage of static methods over getters/setters here?

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Honestly I'm not really sure how to articulate the preference. It's something I've seen done with flag properties before but I can't find a justification other than "it'd look more familiar to me based on other code I've seen".

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I like this style because it makes the properties accessible the same way they were before, but yeah, ultimately no strong preferences here from my side, I was just curious.

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I was honestly convinced I had a good reason before you asked so thanks for asking and making me think about it. Very easy to fall into familiar patterns.

return Boolean(this.flags & FLAG_ONCE);
}
get capture() {
return Boolean(this.flags & FLAG_CAPTURE);
}
get passive() {
return Boolean(this.flags & FLAG_PASSIVE);
}
get isNodeEventTarget() {
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return Boolean(this.flags & FLAG_NODE_STYLE);
}
get weak() {
return Boolean(this.flags & FLAG_WEAK);
}
get removed() {
return Boolean(this.flags & FLAG_REMOVED);
}
set removed(value) {
if (value)
this.flags |= FLAG_REMOVED;
else
this.flags &= ~FLAG_REMOVED;
}

same(listener, capture) {
const myListener = this.weak ? this.listener.deref() : this.listener;
return myListener === listener && this.capture === capture;
Expand Down