fix(rivetkit): stall stop handler until start completes by MasterPtato · Pull Request #4192 · rivet-dev/rivet

MasterPtato · 2026-02-13T21:53:48Z

Description

Please include a summary of the changes and the related issue. Please also include relevant motivation and context.

Type of change

Bug fix (non-breaking change which fixes an issue)
New feature (non-breaking change which adds functionality)
Breaking change (fix or feature that would cause existing functionality to not work as expected)
This change requires a documentation update

How Has This Been Tested?

Please describe the tests that you ran to verify your changes.

Checklist:

My code follows the style guidelines of this project
I have performed a self-review of my code
I have commented my code, particularly in hard-to-understand areas
I have made corresponding changes to the documentation
My changes generate no new warnings
I have added tests that prove my fix is effective or that my feature works
New and existing unit tests pass locally with my changes

railway-app · 2026-02-13T21:53:56Z

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MasterPtato · 2026-02-13T21:54:04Z

fix(rivetkit): stall stop handler until start completes #4192 👈 (View in Graphite)
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claude · 2026-02-13T21:57:21Z

PR Review: fix(rivetkit): stall stop handler until start completes

Summary

This PR fixes a race condition in EngineActorDriver where #runnerOnActorStop could be called before #runnerOnActorStart finishes, leaving an orphaned handler in #actors and skipping onStop. The fix is correct and well-targeted.

Core Fix Analysis (`actor-driver.ts`)

The bug: #actors.delete(actorId) was inside the if (handler?.actor) block. If stop arrived before the actor fully started (handler.actor not yet set), the handler was never removed from the map — a leak.

The fix: moves delete unconditionally after the stop logic and adds an await handler.actorStartPromise.promise gate so stop properly serializes behind start.

This is the right approach. One observation: after await handler.actorStartPromise.promise, we still hold the pre-await handler reference. Since handler is an object reference (not a copy) and the map value is mutated in-place (e.g. handler.actor = ..., handler.actorStartPromise = undefined), this is correct — the local reference reflects the live state after start completes.

Potential double-stop concern: If #runnerOnActorStop is called concurrently for the same actorId (unlikely but possible), both calls would capture the same handler before either deletes it, both would await the start promise, and both would call onStop. This isn't introduced by this PR, but the new async gap makes it slightly more reachable. Worth noting as a follow-up.

Tests (`actor-lifecycle.ts`)

Test: "onDestroy is called even when actor is destroyed during start" — this test has a likely ordering bug:

const statePromise = actor.getState();   // (1) enqueues getState
await actor.destroy();                   // (2) waits for start, then stops actor
const state = await statePromise;        // (3) awaits getState result
expect(state.destroyCalled).toBe(true);  // expects onDestroy already ran

With the fix, the sequence is: start completes → queued getState action runs (returning destroyCalled: false) → actor stops → onDestroy sets destroyCalled: true. The action result from step (3) would be false, not true. This test will likely fail or pass only by coincidence.

Test: "multiple rapid create/destroy cycles..." — the assertion expect(true).toBe(true) is an anti-pattern. If the intent is just "no error thrown," the assertion can be removed (Vitest will pass the test if no exception is thrown).

Unused fixture: lifecycleObserver is added to the registry but not used in any test in this PR. It should either be used or removed to avoid dead code.

Tests (`conn-error-serialization.ts`)

Cleanup not in finally: The conn.dispose() call in both tests sits after the assertion, so if an assertion fails the dispose never runs. Consider wrapping with try/finally:

const conn = actor.connect();
try {
  await conn.getValue();
} catch (err) {
  caughtError = err;
} finally {
  await conn.dispose();
}

This is especially relevant for the error-path test where conn may be in a failed state — disposing a never-established connection may also need to be handled gracefully.

Linter / Style

The Graphite bot already flagged the { } spacing in empty arrow functions (Biome prefers {}). These are minor formatting issues that should be fixed to pass CI.

Overall

The fix is correct and addresses a real race condition. Main items before merge:

Fix the ordering assumption in the destroyCalled test or remove the assertion
Remove unused lifecycleObserver fixture or add a test that uses it
Move conn.dispose() to finally blocks in the error serialization tests
Fix Biome formatting ({} vs { } in empty callbacks)

graphite-app · 2026-02-13T22:06:03Z

rivetkit-typescript/packages/rivetkit/src/drivers/engine/actor-driver.ts

 				this.#runnerStarted.resolve(undefined);
 			},
-			onDisconnected: (_code, _reason) => {},
+			onDisconnected: (_code, _reason) => { },


Remove spaces inside the empty function braces to comply with Biome linter formatting rules. Change onDisconnected: (_code, _reason) => { }, to onDisconnected: (_code, _reason) => {},

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graphite-app · 2026-02-13T22:06:07Z

rivetkit-typescript/packages/rivetkit/src/drivers/engine/actor-driver.ts

 		return streamSSE(c, async (stream) => {
 			// NOTE: onAbort does not work reliably
-			stream.onAbort(() => {});
+			stream.onAbort(() => { });


Remove spaces inside the empty function braces to comply with Biome linter formatting rules. Change stream.onAbort(() => { }); to stream.onAbort(() => {});

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graphite-app · 2026-02-13T22:09:00Z

rivetkit-typescript/packages/rivetkit/fixtures/driver-test-suite/start-stop-race.ts

+import { actor } from "rivetkit";
+
+/**
+ * Actor designed to test start/stop race conditions.
+ * Has a slow initialization to make race conditions easier to trigger.
+ */
+export const startStopRaceActor = actor({
+	state: {
+		initialized: false,
+		startTime: 0,
+		destroyCalled: false,
+		startCompleted: false,
+	},
+	onWake: async (c) => {
+		c.state.startTime = Date.now();
+
+		// Simulate slow initialization to create window for race condition
+		await new Promise((resolve) => setTimeout(resolve, 100));
+
+		c.state.initialized = true;
+		c.state.startCompleted = true;
+	},
+	onDestroy: (c) => {
+		c.state.destroyCalled = true;
+		// Don't save state here - the actor framework will save it automatically
+	},
+	actions: {
+		getState: (c) => {
+			return {
+				initialized: c.state.initialized,
+				startTime: c.state.startTime,
+				destroyCalled: c.state.destroyCalled,
+				startCompleted: c.state.startCompleted,
+			};
+		},
+		ping: (c) => {
+			return "pong";
+		},
+		destroy: (c) => {
+			c.destroy();
+		},
+	},
+});
+
+/**
+ * Observer actor to track lifecycle events from other actors
+ */
+export const lifecycleObserver = actor({
+	state: {
+		events: [] as Array<{
+			actorKey: string;
+			event: string;
+			timestamp: number;
+		}>,
+	},
+	actions: {
+		recordEvent: (c, params: { actorKey: string; event: string }) => {
+			c.state.events.push({
+				actorKey: params.actorKey,
+				event: params.event,
+				timestamp: Date.now(),
+			});
+		},
+		getEvents: (c) => {
+			return c.state.events;
+		},
+		clearEvents: (c) => {
+			c.state.events = [];
+		},
+	},
+});


Run the Biome formatter on this file to ensure proper formatting and sorted imports. The file is new and likely has formatting issues that don't match the project's style guide.

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graphite-app · 2026-02-13T22:55:45Z

rivetkit-typescript/packages/rivetkit/fixtures/driver-test-suite/registry.ts

+import { startStopRaceActor, lifecycleObserver } from "./start-stop-race";
+import { connErrorSerializationActor } from "./conn-error-serialization";


Imports should be sorted alphabetically. Consider reordering these imports to maintain consistent sorting.

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graphite-app · 2026-02-13T22:55:47Z

rivetkit-typescript/packages/rivetkit/src/driver-test-suite/mod.ts

 import { runActorConnHibernationTests } from "./tests/actor-conn-hibernation";
 import { runActorConnStateTests } from "./tests/actor-conn-state";
 import { runActorDbTests } from "./tests/actor-db";
+import { runConnErrorSerializationTests } from "./tests/conn-error-serialization";


This import should be sorted alphabetically with the other imports to maintain consistent ordering.

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pkg-pr-new · 2026-02-18T02:19:15Z

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commit: 3e27725

MasterPtato requested a review from NathanFlurry February 13, 2026 21:53

railway-app bot had a problem deploying to rivet-frontend / rivet-pr-4192 February 13, 2026 21:53 Failure

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MasterPtato force-pushed the 02-13-fix_rivetkit_stall_stop_handler_until_start_completes branch from 1b0d832 to 0f6bab1 Compare February 13, 2026 22:51

railway-app bot had a problem deploying to rivet-frontend / rivet-pr-4192 February 13, 2026 22:51 Failure

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MasterPtato force-pushed the 02-13-fix_rivetkit_stall_stop_handler_until_start_completes branch from 0f6bab1 to 8f7b569 Compare February 18, 2026 02:14

railway-app bot had a problem deploying to rivet-frontend / rivet-pr-4192 February 18, 2026 02:14 Failure

fix(rivetkit): stall stop handler until start completes

3e27725

MasterPtato force-pushed the 02-13-fix_rivetkit_stall_stop_handler_until_start_completes branch from 8f7b569 to 3e27725 Compare February 19, 2026 22:53

railway-app bot had a problem deploying to rivet-frontend / rivet-pr-4192 February 19, 2026 22:53 Failure

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fix(rivetkit): stall stop handler until start completes#4192

fix(rivetkit): stall stop handler until start completes#4192
MasterPtato wants to merge 1 commit intomainfrom
02-13-fix_rivetkit_stall_stop_handler_until_start_completes

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		import { startStopRaceActor, lifecycleObserver } from "./start-stop-race";
		import { connErrorSerializationActor } from "./conn-error-serialization";

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MasterPtato commented Feb 13, 2026

Description

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How Has This Been Tested?

Checklist:

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PR Review: fix(rivetkit): stall stop handler until start completes

Summary

Core Fix Analysis (actor-driver.ts)

Tests (actor-lifecycle.ts)

Tests (conn-error-serialization.ts)

Linter / Style

Overall

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Core Fix Analysis (`actor-driver.ts`)

Tests (`actor-lifecycle.ts`)

Tests (`conn-error-serialization.ts`)

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