fix: Android app crashing on hot-restart in debug mode

CHANGELOG.md

@@ -4,6 +4,7 @@
 
 ### Fixes
 
+- Android app crashing on hot-restart in debug mode ([#3358](https://github.com/getsentry/sentry-dart/pull/3358))
 - Dont use `Companion` in JNI calls and properly release JNI refs ([#3354](https://github.com/getsentry/sentry-dart/pull/3354))
   - This potentially fixes segfault crashes related to JNI
 

packages/flutter/android/src/main/kotlin/io/sentry/flutter/SafeReplayRecorderCallbacks.kt

@@ -0,0 +1,68 @@
+package io.sentry.flutter
+
+import android.util.Log
+import java.util.concurrent.atomic.AtomicInteger
+
+/**
+ * Wraps [ReplayRecorderCallbacks] and guards all callbacks behind a generation check (to ignore stale callbacks from previous isolates).
+ * Without this check the app would crash after a hot-restart in debug mode.
+ */
+internal class SafeReplayRecorderCallbacks(
+  private val delegate: ReplayRecorderCallbacks,
+) : ReplayRecorderCallbacks {
+  companion object {
+    private val generationCounter = AtomicInteger(0)
+
+    fun bumpGeneration() {
+      generationCounter.incrementAndGet()
+    }
+
+    fun currentGeneration(): Int = generationCounter.get()
+  }
+
+  private val generationSnapshot: Int = currentGeneration()
+
+  private inline fun guard(block: () -> Unit) {
+    if (generationSnapshot != currentGeneration()) return
+    try {
+      block()
+    } catch (t: Throwable) {
+      Log.w("Sentry", "Replay recorder callback failed", t)
+    }
+  }
+
+  override fun replayStarted(
+    replayId: String,
+    replayIsBuffering: Boolean,
+  ) = guard {
+    delegate.replayStarted(replayId, replayIsBuffering)
+  }
+
+  override fun replayResumed() =
+    guard {
+      delegate.replayResumed()
+    }
+
+  override fun replayPaused() =
+    guard {
+      delegate.replayPaused()
+    }
+
+  override fun replayStopped() =
+    guard {
+      delegate.replayStopped()
+    }
+
+  override fun replayReset() =
+    guard {
+      delegate.replayReset()
+    }
+
+  override fun replayConfigChanged(
+    width: Int,
+    height: Int,
+    frameRate: Int,
+  ) = guard {
+    delegate.replayConfigChanged(width, height, frameRate)
+  }
+}

packages/flutter/android/src/main/kotlin/io/sentry/flutter/SentryFlutterPlugin.kt

@@ -71,6 +71,7 @@ class SentryFlutterPlugin :
       return
     }
 
+    tearDownReplayIntegration()
     channel.setMethodCallHandler(null)
     applicationContext = null
   }
@@ -111,6 +112,25 @@ class SentryFlutterPlugin :
 
     private const val NATIVE_CRASH_WAIT_TIME = 500L
 
+    /**
+     * Tears down the current ReplayIntegration to avoid invoking callbacks from a stale
+     * Flutter isolate after hot restart.
+     *
+     * - Bumps the replay callback generation so any pending posts from the previous
+     *   isolate no-op.
+     * - Closes the existing ReplayIntegration and clears its reference.
+     */
+    fun tearDownReplayIntegration() {
+      SafeReplayRecorderCallbacks.bumpGeneration()
+      try {
+        replay?.close()
+      } catch (e: Exception) {
+        Log.w("Sentry", "Failed to close existing ReplayIntegration", e)
+      } finally {
+        replay = null
+      }
+    }
+
     @Suppress("unused") // Used by native/jni bindings
     @JvmStatic
     fun privateSentryGetReplayIntegration(): ReplayIntegration? = replay
@@ -120,6 +140,8 @@ class SentryFlutterPlugin :
       options: SentryAndroidOptions,
       replayCallbacks: ReplayRecorderCallbacks?,
     ) {
+      tearDownReplayIntegration()
+
       // Replace the default ReplayIntegration with a Flutter-specific recorder.
       options.integrations.removeAll { it is ReplayIntegration }
       val replayOptions = options.sessionReplay
@@ -130,12 +152,14 @@ class SentryFlutterPlugin :
           return
         }
 
+        val safeCallbacks = SafeReplayRecorderCallbacks(replayCallbacks)
+
         replay =
           ReplayIntegration(
             ctx.applicationContext,
             dateProvider = CurrentDateProvider.getInstance(),
             recorderProvider = {
-              SentryFlutterReplayRecorder(replayCallbacks, replay!!)
+              SentryFlutterReplayRecorder(safeCallbacks, replay!!)
             },
             replayCacheProvider = null,
           )