Fix an issue that clearing the image cache may cause resource leaks (flutter#104527)

Author: yeatse

packages/flutter/lib/src/painting/image_cache.dart

@@ -397,16 +397,16 @@ class ImageCache {
     if (!kReleaseMode) {
       listenerTask = TimelineTask(parent: timelineTask)..start('listener');
     }
-    // If we're doing tracing, we need to make sure that we don't try to finish
-    // the trace entry multiple times if we get re-entrant calls from a multi-
-    // frame provider here.
+    // A multi-frame provider may call the listener more than once. We need do make
+    // sure that some cleanup works won't run multiple times, such as finishing the
+    // tracing task or removing the listeners
     bool listenedOnce = false;
 
     // We shouldn't use the _pendingImages map if the cache is disabled, but we
     // will have to listen to the image at least once so we don't leak it in
     // the live image tracking.
-    // If the cache is disabled, this variable will be set.
-    _PendingImage? untrackedPendingImage;
+    final bool trackPendingImage = maximumSize > 0 && maximumSizeBytes > 0;
+    late _PendingImage pendingImage;
     void listener(ImageInfo? info, bool syncCall) {
       int? sizeBytes;
       if (info != null) {
@@ -421,14 +421,14 @@ class ImageCache {
       _trackLiveImage(key, result, sizeBytes);
 
       // Only touch if the cache was enabled when resolve was initially called.
-      if (untrackedPendingImage == null) {
+      if (trackPendingImage) {
         _touch(key, image, listenerTask);
       } else {
         image.dispose();
       }
 
-      final _PendingImage? pendingImage = untrackedPendingImage ?? _pendingImages.remove(key);
-      if (pendingImage != null) {
+      _pendingImages.remove(key);
+      if (!listenedOnce) {
         pendingImage.removeListener();
       }
       if (!kReleaseMode && !listenedOnce) {
@@ -445,10 +445,9 @@ class ImageCache {
     }
 
     final ImageStreamListener streamListener = ImageStreamListener(listener);
-    if (maximumSize > 0 && maximumSizeBytes > 0) {
-      _pendingImages[key] = _PendingImage(result, streamListener);
-    } else {
-      untrackedPendingImage = _PendingImage(result, streamListener);
+    pendingImage = _PendingImage(result, streamListener);
+    if (trackPendingImage) {
+      _pendingImages[key] = pendingImage;
     }
     // Listener is removed in [_PendingImage.removeListener].
     result.addListener(streamListener);

packages/flutter/test/painting/image_cache_test.dart

@@ -332,6 +332,33 @@ void main() {
     expect(imageCache.liveImageCount, 0);
   });
 
+  test('Clearing image cache does not leak live images', () async {
+    imageCache.maximumSize = 1;
+
+    final ui.Image testImage1 = await createTestImage(width: 8, height: 8);
+    final ui.Image testImage2 = await createTestImage(width: 10, height: 10);
+
+    final TestImageStreamCompleter completer1 = TestImageStreamCompleter();
+    final TestImageStreamCompleter completer2 = TestImageStreamCompleter()..testSetImage(testImage2);
+
+    imageCache.putIfAbsent(testImage1, () => completer1);
+    expect(imageCache.statusForKey(testImage1).pending, true);
+    expect(imageCache.statusForKey(testImage1).live, true);
+
+    imageCache.clear();
+    expect(imageCache.statusForKey(testImage1).pending, false);
+    expect(imageCache.statusForKey(testImage1).live, true);
+
+    completer1.testSetImage(testImage1);
+    expect(imageCache.statusForKey(testImage1).keepAlive, true);
+    expect(imageCache.statusForKey(testImage1).live, false);
+
+    imageCache.putIfAbsent(testImage2, () => completer2);
+    expect(imageCache.statusForKey(testImage1).tracked, false); // evicted
+    expect(imageCache.statusForKey(testImage2).tracked, true);
+  });
+
+
   test('Evicting a pending image clears the live image by default', () async {
     final ui.Image testImage = await createTestImage(width: 8, height: 8);