feat: Devtools - A separate, lightweight event bus -- utilizing Dispatch (Sync) by theVedanta · Pull Request #950 · uwdata/mosaic

theVedanta · 2025-12-25T00:41:59Z

This commit resolves some tasks discussed in the meeting with @domoritz. In response to the issue #943
For an overview, these are some of the immediate action items discussed:

Action items

The UI-related example, written in Solid JS, will be in a separate PR. The current goal is to switch out the logger in Coordinator and QueryManager to consume our event bus for uncertain event types (which will be crystallized later for devtools).

https://docs.google.com/document/d/1cyw2sv9G5-CzGG-JgeOEcISSu7zmEqdzsa-J2oh2F6c/edit?tab=t.0

domoritz

Very cool start. looking good. Here are some comments.

domoritz · 2026-01-07T20:15:38Z

  function setQueryLog() {
-    vg.coordinator().manager.logQueries(qlogToggle.checked);
+    // logQueries is no longer in use
+    // vg.coordinator().manager.logQueries(qlogToggle.checked);


This is where we should add or remove our custom observer that redirects events to console.

domoritz · 2026-01-07T20:16:56Z

+   *  callback function to remove.
+   */
+  override removeEventListener(type: string, callback: EventCallback<T>): void {
+    super.removeEventListener(type, callback);


do we need this override? Looks equivalent

I think I had some extensibility in mind for later, but on at another glance, I think this feels unnecessary. Removing...

domoritz · 2026-01-07T20:19:13Z

    if (arguments.length) {
      this._logger = logger || voidLogger();
      this.manager.logger(this._logger);
+      // subscribe logger to events


Looks good as a stepping stone but I think we can go ahead and make the logger a separate observer that users need to explicitly add. We can remove the logger entirely now imo.

domoritz · 2026-01-07T20:19:43Z

  ): Promise<unknown> {
    client.queryPending();
-    return client._pending = this.query(query, { priority })
+    return client._pending = this.query(query, { priority, clientId: (client as any).id })


as any is worrying me a bit here

I'm thinking we get rid of the clientId for now?

Let's do that

domoritz · 2026-01-31T03:42:42Z

      output.replaceChildren();
    } else {
-      await coordinator().exec(
+      await vg.coordinator().exec(


why do we need to add vg.?

honestly, I'm not really sure. this example was broken when I tested it; the coordinator is not accessible as an object here, but only as a property of vg

Ahh, good catch. I'll fix it separately. Let's keep PRs focused on one thing.

Done in #965. Let's remove this here.

domoritz · 2026-01-31T03:50:57Z

    enable();
  });
+
+  function setQueryLog() {


Shouldn't this logic (which replicates the old logger, right?) be in mosaic core so that people can easily get the old logger behavior again?

ahh. we can definitely do that. My mistake, I felt that when we said 'remove the logger from core entirely,' we give the client the option to write that logic. I can put this function in core to give back a logger util to the user/client (perhaps we can discuss that idea some more (?))

IIRC the idea was to remove the logger but give users an equivalent tool via the new bus.

domoritz · 2026-01-31T03:52:50Z

-    vg.coordinator().manager.logQueries(qlogToggle.checked);
+    const bus = vg.coordinator().eventBus;
+
+    bus.observe("QueryStart", (event) =>


duplicated logic?

domoritz · 2026-01-31T04:00:55Z

        if (cached) {
-          const data = await cached;
-          this._logger.debug('Cache');
+          const data = cached;


Do we not need to await anymore?

await will have no effect here

Let's make a separate pull request. IIRC there was some reason where cached results can be promises but I am not 100% sure right now.

domoritz · 2026-01-31T04:01:50Z

+      this.eventBus?.emit(EventType.Error, {
+        message: err,
+      });


Is this strictly needed to replicate the behavior of the old logger?

Well, all it's doing it just pipe whatever the message was (which logger emitted) into the bus, which is now consumable by anyone, including the logger. I don't know if Im missing something, did you have a simpler approach in mind?

I just didn't see a log message (we removed) here before so I am wondering whether the emit is needed.

domoritz · 2026-01-31T04:03:03Z

+  Error = "error",
+}
+
+export type EventMap = {


I've never seen this pattern before. Why is this needed?

This was mainly for type-safety (for us and the clients)

Let's not do this and instead use the class approach I suggested?

domoritz · 2026-01-31T04:04:04Z

+  QueryStart = "query-start",
+  QueryEnd = "query-end",
+  ClientConnect = "client-connect",
+  ClientStateChange = "client-state-change",


Should this still be here?

sorry? I don't understand

I don't see client-state-change used anywhere.

domoritz · 2026-01-31T04:05:06Z

@@ -0,0 +1,43 @@
+export enum EventType {


Instead of having this enum here. Wouldn't it be easier to have classes for the events that can be instantiated with a constructor?

That is probably true. It will get rid of this "broken"-ish type interface for the events. But I remember that we agreed on enums (denoted by strings instead of numbers) to provide the user a simple list of event types in autocomplete

Yeah, we can still use enums in the event types but in order to create an event object, we could use a class. Maybe it's cleaner to actually put the event type into the message so that we can easily type check a message in isolation. Let's do that.

theVedanta · 2026-03-31T20:09:16Z

@domoritz let me know if the current approach is closer to the logger implementation you had in mind. If not, we can perhaps meet again and clear up any confusion.

theVedanta added 4 commits December 24, 2025 18:32

observe dispatch (sync)

859468e

small change in cancel()

1cfd7ef

terminology -- observe

5fe505c

Event bus and logger observe() API in effect

8dcba1c

domoritz reviewed Jan 7, 2026

View reviewed changes

Comment thread packages/mosaic/core/src/QueryManager.ts Outdated

theVedanta added 4 commits January 7, 2026 23:11

timestamp + abstractions

0f8cec0

Moving logger on client as observer

8a7b56e

removed client id

3cd95e0

removed event bus & replaced w/ ObserveDispatch

be0b792

domoritz reviewed Jan 10, 2026

View reviewed changes

Comment thread packages/mosaic/core/src/Coordinator.ts Outdated

domoritz reviewed Jan 10, 2026

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Comment thread packages/mosaic/core/src/Events.ts Outdated

domoritz reviewed Jan 10, 2026

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Comment thread packages/mosaic/core/src/Events.ts Outdated

theVedanta added 2 commits January 17, 2026 07:52

stronger typesafety

353fcaa

logger removed -- client now subscribes with eventBus

a5990bb

domoritz reviewed Jan 19, 2026

View reviewed changes

Comment thread packages/mosaic/core/src/util/ObserveDispatch.ts Outdated

domoritz reviewed Jan 19, 2026

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Comment thread packages/mosaic/core/src/Coordinator.ts Outdated

domoritz reviewed Jan 19, 2026

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Comment thread .prettierrc.json Outdated

overlooked errors

d37a487

theVedanta changed the title ~~feat: Devtools v2 -- Creates a separate, lightweight event bus~~ feat: Devtools - A separate, lightweight event bus -- utilizing Dispatch (Sync) Jan 20, 2026

theVedanta marked this pull request as ready for review January 24, 2026 21:36

theVedanta requested a review from jheer as a code owner January 24, 2026 21:36

theVedanta requested a review from domoritz January 28, 2026 22:26

domoritz requested changes Jan 31, 2026

View reviewed changes

theVedanta added 5 commits March 3, 2026 12:41

warning type

cd9a4e2

merge

75153b1

merge-related changes

820a8cc

more merge changes

b6999f7

devtools bus map changed + logger separately added

c8a2c3f

more merge

d89ca14

SeanCassiere mentioned this pull request May 13, 2026

feat: event bus support for devtools #1028

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theVedanta commented Dec 25, 2025 •

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