Move prefetch vote tracking into IosPrefetchScheduler

compose/ui/ui/src/iosMain/kotlin/androidx/compose/ui/scene/ComposeSceneMediator.ios.kt

@@ -214,16 +214,12 @@ internal class ComposeSceneMediator(
 
     private val isActive get() = coroutineContext.isActive
 
-    private var isPrefetchVoteActive: Boolean = false // TODO CMP-10587: Move inside the IosPrefetchScheduler
     private val prefetchScheduler = IosPrefetchScheduler(
-        onHasWorkScheduled = { hasWork ->
-            if (hasWork != isPrefetchVoteActive) {
-                isPrefetchVoteActive = hasWork
-                if (hasWork) {
-                    activitiesHandler.onActivitiesStarted()
-                } else {
-                    activitiesHandler.onActivitiesEnded()
-                }
+        onPrefetchVoteChanged = { isVoteActive ->
+            if (isVoteActive) {
+                activitiesHandler.onActivitiesStarted()
+            } else {
+                activitiesHandler.onActivitiesEnded()
             }
         }
     )

compose/ui/ui/src/iosMain/kotlin/androidx/compose/ui/window/IosPrefetchScheduler.ios.kt

@@ -28,12 +28,19 @@ import platform.QuartzCore.CACurrentMediaTime
 
 internal class IosPrefetchScheduler(
     private val currentTime: () -> NSTimeInterval = { CACurrentMediaTime() },
-    private var onHasWorkScheduled: (Boolean) -> Unit,
+    private var onPrefetchVoteChanged: (Boolean) -> Unit,
 ) : PlatformPrefetchScheduler {
     private val scheduledPrefetchRequests = ScheduledPrefetchRequests()
     private val scope = PrefetchRequestScopeImpl()
     private val hasWorkScheduled: Boolean get() = scheduledPrefetchRequests.hasWorkScheduled
 
+    /**
+     * Whether the scheduler currently votes for prefetch activities to be running.
+     *
+     * Tracked here so [onPrefetchVoteChanged] is only invoked when the vote actually changes.
+     */
+    private var isPrefetchVoteActive: Boolean = false
+
     /**
      * Marks the start of the display-link interval where drawing happened.
      */
@@ -73,7 +80,7 @@ internal class IosPrefetchScheduler(
         }
 
         scheduledPrefetchRequests.addHighPriority(request)
-        onHasWorkScheduled(hasWorkScheduled)
+        updatePrefetchVote(hasWorkScheduled)
     }
 
     override fun scheduleLowPriorityPrefetch(request: PlatformPrefetchRequest) {
@@ -86,7 +93,7 @@ internal class IosPrefetchScheduler(
         }
 
         scheduledPrefetchRequests.addLowPriority(request)
-        onHasWorkScheduled(hasWorkScheduled)
+        updatePrefetchVote(hasWorkScheduled)
     }
 
     /**
@@ -106,7 +113,7 @@ internal class IosPrefetchScheduler(
             "IosPrefetchScheduler.execute() must be called on main thread"
         }
         if (isDisposed) {
-            onHasWorkScheduled(false)
+            updatePrefetchVote(false)
             return
         }
 
@@ -119,7 +126,7 @@ internal class IosPrefetchScheduler(
         }
 
         if (!hasWorkScheduled) {
-            onHasWorkScheduled(false)
+            updatePrefetchVote(false)
             return
         }
 
@@ -137,7 +144,7 @@ internal class IosPrefetchScheduler(
                 }
         }
 
-        onHasWorkScheduled(hasWorkScheduled)
+        updatePrefetchVote(hasWorkScheduled)
         traceValue("compose:lazy:prefetch:available_time_nanos", 0L)
     }
 
@@ -166,8 +173,15 @@ internal class IosPrefetchScheduler(
         }
         isDisposed = true
         scheduledPrefetchRequests.clear()
-        onHasWorkScheduled(false)
-        onHasWorkScheduled = {}
+        updatePrefetchVote(false)
+        onPrefetchVoteChanged = {}
+    }
+
+    private fun updatePrefetchVote(hasWork: Boolean) {
+        if (hasWork != isPrefetchVoteActive) {
+            isPrefetchVoteActive = hasWork
+            onPrefetchVoteChanged(hasWork)
+        }
     }
 
     private fun executeRequest(): Boolean {

compose/ui/ui/src/iosTest/kotlin/androidx/compose/ui/window/PlatformPrefetchSchedulerTest.kt

@@ -91,34 +91,46 @@ class PlatformPrefetchSchedulerTest {
     }
 
     @Test
-    fun testReportsNoScheduledWorkWhenNoRequestsAreScheduledAndDidNotDraw() {
-        val hasWorkEvents = mutableListOf<Boolean>()
-        val scheduler = scheduler(onHasWorkScheduled = hasWorkEvents::add)
+    fun testDoesNotVoteForPrefetchWhenNoRequestsAreScheduledAndDidNotDraw() {
+        val prefetchVoteEvents = mutableListOf<Boolean>()
+        val scheduler = scheduler(onPrefetchVoteChanged = prefetchVoteEvents::add)
 
         scheduler.execute(lastFrameTimestamp = 0.0, targetTimestamp = 1.0, didDraw = false)
 
-        assertEquals(listOf(false), hasWorkEvents)
+        assertTrue(prefetchVoteEvents.isEmpty())
     }
 
     @Test
-    fun testReportsNoScheduledWorkWhenNoRequestsAreScheduledAndDidDraw() {
-        val hasWorkEvents = mutableListOf<Boolean>()
-        val scheduler = scheduler(onHasWorkScheduled = hasWorkEvents::add)
+    fun testDoesNotVoteForPrefetchWhenNoRequestsAreScheduledAndDidDraw() {
+        val prefetchVoteEvents = mutableListOf<Boolean>()
+        val scheduler = scheduler(onPrefetchVoteChanged = prefetchVoteEvents::add)
 
         scheduler.execute(lastFrameTimestamp = 0.0, targetTimestamp = 1.0, didDraw = true)
 
-        assertEquals(listOf(false), hasWorkEvents)
+        assertTrue(prefetchVoteEvents.isEmpty())
     }
 
     @Test
-    fun testReportsNoScheduledWorkWhenQueueDrains() {
-        val hasWorkEvents = mutableListOf<Boolean>()
-        val scheduler = scheduler(onHasWorkScheduled = hasWorkEvents::add)
+    fun testVotesForPrefetchWhileWorkIsScheduledAndEndsWhenQueueDrains() {
+        val prefetchVoteEvents = mutableListOf<Boolean>()
+        val scheduler = scheduler(onPrefetchVoteChanged = prefetchVoteEvents::add)
 
         scheduler.scheduleLowPriorityPrefetch(request("request"))
         scheduler.execute(lastFrameTimestamp = 0.0, targetTimestamp = 1.0, didDraw = false)
 
-        assertEquals(listOf(true, false), hasWorkEvents)
+        assertEquals(listOf(true, false), prefetchVoteEvents)
+    }
+
+    @Test
+    fun testDoesNotEmitDuplicatePrefetchVotes() {
+        val prefetchVoteEvents = mutableListOf<Boolean>()
+        val scheduler = scheduler(onPrefetchVoteChanged = prefetchVoteEvents::add)
+
+        scheduler.scheduleLowPriorityPrefetch(request("request-0"))
+        scheduler.scheduleLowPriorityPrefetch(request("request-1"))
+        scheduler.execute(lastFrameTimestamp = 0.0, targetTimestamp = 1.0, didDraw = false)
+
+        assertEquals(listOf(true, false), prefetchVoteEvents)
     }
 
     @Test
@@ -169,10 +181,10 @@ class PlatformPrefetchSchedulerTest {
     }
 
     private fun scheduler(
-        onHasWorkScheduled: (Boolean) -> Unit = {},
+        onPrefetchVoteChanged: (Boolean) -> Unit = {},
         currentTime: () -> NSTimeInterval = { 0.0 },
     ) = IosPrefetchScheduler(
-        onHasWorkScheduled = onHasWorkScheduled,
+        onPrefetchVoteChanged = onPrefetchVoteChanged,
         currentTime = currentTime,
     )