fix: eliminate JPromise listener leak and SafeContinuation deadlock (#1439)

[skjolber]

This PR is again generated by AI, most code changes unfortunately are a bit over my head. But it is much cleaner than #1440 and also actually attempts to fix the relevant issues.

Problem

When a JS async callback is invoked twice in sequence from a native Java background thread,
the second call hangs forever. This was reported in real-world usage where a downstream SDK's
Java code calls Promise.await() using a raw Continuation (the CustomContinuation pattern
common in Java coroutine interop).

Two bugs compound to cause the hang:

Bug 1 — Wrong-state listener registration (JPromise.hpp)

addOnResolvedListener on an already-rejected JPromise (and the symmetric
addOnRejectedListener on an already-resolved one) fell through the plain else branch.
The listener was silently pushed into _onResolvedListeners / _onRejectedListeners — a queue
that would never be drained. The listener and everything it captured were retained for the
lifetime of the JPromise.

Bug 2 — SafeContinuation fast-path skips resumeWith (Promise.kt)

await() used suspendCoroutine, which wraps the caller's continuation in a SafeContinuation.
When the Promise is already resolved at the time await() is called,
SafeContinuation::resumeWith() stores the value and getOrThrow() returns it directly —
without ever calling delegate.resumeWith(). Java callers that block on
CompletableFuture.get() after calling await() therefore hang forever, because
CustomContinuation.resumeWith() is never invoked.

Fix

JPromise.hpp — add explicit else if guards for the opposite-settled state:

• addOnResolvedListener on a rejected promise → discard the listener
• addOnRejectedListener on a resolved promise → discard the listener
• resolve() / reject() dispatch listeners outside the lock (mirrors C++ Promise<T>)
  and clear the opposite listener vector immediately

Promise.kt — replace suspendCoroutine with suspendCoroutineUninterceptedOrReturn

• intercepted():

// Before — SafeContinuation fast-path skips resumeWith when already resolved:
suspend fun await(): T = suspendCoroutine { continuation ->
    then { result -> continuation.resume(result) }
    catch { error -> continuation.resumeWithException(error) }
}

// After — resumeWith is always called on the underlying continuation:
suspend fun await(): T = suspendCoroutineUninterceptedOrReturn { uCont ->
    val cont = uCont.intercepted()
    then { result -> cont.resumeWith(Result.success(result)) }
    catch { error -> cont.resumeWith(Result.failure(error)) }
    COROUTINE_SUSPENDED
}

By always returning COROUTINE_SUSPENDED and routing all results through cont.resumeWith(),
the underlying continuation — including any Java-side CustomContinuation — is always invoked
regardless of whether the Promise was already settled at call time. .intercepted() preserves
correct dispatcher behaviour for Kotlin coroutine callers.

Test

Adds callCallbackSequentiallyFirstThrows to TestObjectSwiftKotlin along with a
SequentialCallbackInput struct. The method calls a JS async callback twice from a
single-threaded Java executor using the CustomContinuation + await() pattern — the exact
pattern from affected downstream SDKs. The first invocation throws; the second must not hang.

	Result
Before fix	timed out after 1552 ms with "Timeouted!"
After fix	✓ passes in 3 ms

The 4 pre-existing ArrayBuffer failures in the suite are unrelated to this PR.

Files changed

File	Change
packages/react-native-nitro-modules/android/src/main/cpp/core/JPromise.hpp	Fix wrong-state listener registration and listener dispatch
packages/react-native-nitro-modules/android/src/main/java/com/margelo/nitro/core/Promise.kt	Fix await() to always call resumeWith
packages/react-native-nitro-test/src/specs/TestObject.nitro.ts	Add SequentialCallbackInput + callCallbackSequentiallyFirstThrows
packages/react-native-nitro-test/android/.../HybridTestObjectKotlin.kt	Kotlin implementation using CustomContinuation + JavaCallHelper
packages/react-native-nitro-test/android/.../CustomContinuation.java	Java Continuation implementation mirroring the real-world anti-pattern
packages/react-native-nitro-test/android/.../JavaCallHelper.java	Java caller that triggers the deadlock via await(continuation) + future.get()
packages/react-native-nitro-test/ios/.../HybridTestObjectSwift.swift	Swift implementation (coroutine-based, not affected by the bug)
example/src/getTests.ts	Failing runtime assertion merged into callback test section
example/__tests__/nitro.harness.ts	Test wired into TestObject (Swift/Kotlin) harness describe block

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1 Skipped Deployment

Project	Deployment	Actions	Updated (UTC)
nitro-docs	Skipped		Jul 17, 2026 6:07pm