feat: Devtools - A separate, lightweight event bus -- utilizing Dispatch (Sync) #950

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

dev/index.html

  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

packages/mosaic/core/src/util/AsyncDispatch.ts

+   *  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

packages/mosaic/core/src/Coordinator.ts

    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

packages/mosaic/core/src/Coordinator.ts

  ): 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 · 2026-01-07T20:20:26Z

packages/mosaic/core/src/Coordinator.ts

      .then(
        data => client.queryResult(data).update(),
-        err => { this._logger?.error(err); client.queryError(err); }
+        err => { this.eventBus.emit(EventType.Error, { message: err, timestamp: Date.now() }); client.queryError(err); }


I wonder whether we really need timestamps since the event bus could maybe automatically add it for all emitted events? Could make the callsites simpler.

absolutely, lemme go ahead and do that

domoritz · 2026-01-07T20:23:15Z

packages/mosaic/core/src/EventBus.ts

+  timestamp: number;
+}
+
+export class EventBus {


Why do we need this class? It seems to just be dispatching events to the ObservableDispatch anyway. If we make the latter generic, we may not need this class at all.

I wondered about just using ObservableDispatch too, but I feel that a separate EventBus would actually be extensible in the future for various reasons like maintaining a history of events between renders (for frameworks like react/preact/solid/etc). That said, if you would still like for me to just use ObserveDispatch directly, to keep things light, we can definitely do that

Let's keep things light.

domoritz · 2026-01-07T20:24:12Z

packages/mosaic/core/src/QueryManager.ts

        const cached = this.clientCache!.get(sql!);
        if (cached) {
          const data = await cached;
          this._logger.debug('Cache');


Let's remove the logger and replace the same location with the event bus stuff.

domoritz · 2026-01-07T20:24:43Z

packages/mosaic/core/src/QueryManager.ts

          this._logger.debug('Cache');
          result.ready(data);
+          // emit QueryEnd for cached
+          if (this.eventBus) {


It's odd to me that this is after result.ready(data) when previously the logging was happening before.

domoritz · 2026-01-07T20:24:54Z

packages/mosaic/core/src/QueryManager.ts

      this._logger.debug(`Request: ${(performance.now() - t0).toFixed(1)}`);
      result.ready(type === 'exec' ? null : data);
+
+      if (this.eventBus) {


same as above

domoritz · 2026-01-07T20:25:20Z

packages/mosaic/core/src/QueryManager.ts

+        });
+      }
    } catch (err) {
+      if (this.eventBus) {


Is this needed to replicate the logic of the logger? If not, let's not add it yet.

domoritz · 2026-01-07T21:32:13Z

packages/mosaic/core/src/QueryManager.ts

+
+      if (this.eventBus) {
+        this.eventBus.emit(EventType.QueryEnd, {
+          query: sql || '',


If we have an undefined sql, we can just output that.

domoritz · 2026-01-10T16:21:07Z

packages/mosaic/core/src/Coordinator.ts

  public filterGroups = new Map<Selection, FilterGroupEntry>;
  protected _logger: Logger = voidLogger();
-  public eventBus: EventBus;
+  public eventBus: ObserveDispatch<any>; // temporary measures until we finalize event types


Let's use the types we already have. We can expand it later.

domoritz · 2026-01-10T16:21:24Z

packages/mosaic/core/src/Events.ts

+
+export interface MosaicEvent {
+  timestamp: number;
+  // Extend later with more fields


No need to say that here.

the extend later part?

Yeah, the whole comment.

domoritz · 2026-01-10T16:21:45Z

packages/mosaic/core/src/Events.ts

+}
+
+export interface ErrorEvent extends MosaicEvent {
+  message: unknown;


Should it be unknown or string?

string for sure; I don't remember why I typed this as unknown

packages/mosaic/core/src/util/ObserveDispatch.ts

packages/mosaic/core/src/Coordinator.ts

domoritz · 2026-01-19T20:16:42Z

.prettierrc.json

let's do in the other pull request

oh sorry i was just using this locally, my bad

All good. Let me know when you addressed the comments above. I think we are getting close.

Done :) Anything else I may have missed?

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

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

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

packages/mosaic/core/src/util/ObserveDispatch.ts Outdated Show resolved Hide resolved

domoritz reviewed Jan 19, 2026

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packages/mosaic/core/src/Coordinator.ts Outdated Show resolved Hide resolved

domoritz reviewed Jan 19, 2026

View reviewed changes

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

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feat: Devtools - A separate, lightweight event bus -- utilizing Dispatch (Sync) #950

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feat: Devtools - A separate, lightweight event bus -- utilizing Dispatch (Sync) #950

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theVedanta commented Dec 25, 2025 • edited Loading Uh oh! There was an error while loading. Please reload this page.

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theVedanta commented Dec 25, 2025 •

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