Fix flakiness of SubSamplingImageTest#draw_tile_under_centroid_first

saket · Apr 10, 2024 · 42faef8 · 42faef8
1 parent 3230987
commit 42faef8
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diff --git a/...pling-image/src/androidTest/kotlin/me/saket/telephoto/subsampling/SubSamplingImageTest.kt b/...pling-image/src/androidTest/kotlin/me/saket/telephoto/subsampling/SubSamplingImageTest.kt
@@ -344,6 +344,11 @@ class SubSamplingImageTest {
         override suspend fun decodeRegion(region: BitmapRegionTile): ImageBitmap {
           val isBaseTile = region.sampleSize.size == 8
           return if (isBaseTile || !firstNonBaseTileReceived.getAndSet(true)) {
+            if (!isBaseTile) {
+              check(region.bounds == IntRect(0, 1200, 1216, 3265)) {
+                "Incorrect first tile received: $region. Possible race condition?"
+              }
+            }
             real.decodeRegion(region)
           } else {
             delay(Long.MAX_VALUE)

diff --git a/...ampling-image/src/main/kotlin/me/saket/telephoto/subsamplingimage/internal/BitmapCache.kt b/...ampling-image/src/main/kotlin/me/saket/telephoto/subsamplingimage/internal/BitmapCache.kt
@@ -3,6 +3,8 @@ package me.saket.telephoto.subsamplingimage.internal
 import androidx.compose.ui.graphics.ImageBitmap
 import androidx.compose.ui.util.fastForEach
 import kotlinx.coroutines.CoroutineScope
+import kotlinx.coroutines.CoroutineStart
+import kotlinx.coroutines.ExperimentalCoroutinesApi
 import kotlinx.coroutines.Job
 import kotlinx.coroutines.channels.Channel
 import kotlinx.coroutines.delay
@@ -41,7 +43,11 @@ internal class BitmapCache(
         .collect { regions ->
           val tilesToLoad = regions.fastFilter { it !in cachedBitmaps.value }
           tilesToLoad.fastForEach { region ->
-            val job = launch {
+            // CoroutineStart.UNDISPATCHED is used to ensure that the coroutines are executed
+            // in the same order they were launched. Otherwise, the tiles may load in a different
+            // order than what was requested. SubSamplingImageTest#draw_tile_under_centroid_first()
+            // test will also become flaky.
+            val job = launch(start = CoroutineStart.UNDISPATCHED) {
               val bitmap = decoder.decodeRegion(region)
               cachedBitmaps.update { it + (region to Loaded(bitmap)) }
             }