Purge back buffer cache when inactive

Author: knopp

shell/platform/darwin/macos/framework/Source/FlutterSurfaceManager.mm

@@ -8,6 +8,64 @@
 #import <Metal/Metal.h>
 #include <algorithm>
 
+// Cached back buffers will be released after kIdleDelay if there is no activity.
+static const double kIdleDelay = 1.0;
+
+@interface FlutterBackBufferCache () {
+  NSMutableArray<FlutterSurface*>* _surfaces;
+}
+
+@end
+
+@implementation FlutterBackBufferCache
+
+- (instancetype)init {
+  if (self = [super init]) {
+    self->_surfaces = [[NSMutableArray alloc] init];
+  }
+  return self;
+}
+
+- (nullable FlutterSurface*)getSurfaceForSize:(CGSize)size {
+  @synchronized(self) {
+    for (FlutterSurface* surface in _surfaces) {
+      if (CGSizeEqualToSize(surface.size, size)) {
+        FlutterSurface* res = surface;
+        [_surfaces removeObject:surface];
+        return res;
+      }
+    }
+    return nil;
+  }
+}
+
+- (void)replaceWith:(nonnull NSArray<FlutterSurface*>*)surfaces {
+  @synchronized(self) {
+    [_surfaces removeAllObjects];
+    [_surfaces addObjectsFromArray:surfaces];
+  }
+
+  // performSelector:withObject:afterDelay needs to be performed on RunLoop thread
+  [self performSelectorOnMainThread:@selector(reschedule) withObject:nil waitUntilDone:NO];
+}
+
+- (void)onIdle {
+  @synchronized(self) {
+    [_surfaces removeAllObjects];
+  }
+}
+
+- (void)reschedule {
+  [NSObject cancelPreviousPerformRequestsWithTarget:self selector:@selector(onIdle) object:nil];
+  [self performSelector:@selector(onIdle) withObject:nil afterDelay:kIdleDelay];
+}
+
+- (void)dealloc {
+  [NSObject cancelPreviousPerformRequestsWithTarget:self selector:@selector(onIdle) object:nil];
+}
+
+@end
+
 @implementation FlutterSurfacePresentInfo
 @end
 
@@ -17,9 +75,9 @@ @interface FlutterSurfaceManager () {
   CALayer* _containingLayer;
   __weak id<FlutterSurfaceManagerDelegate> _delegate;
 
-  // Available (cached) back buffer surfaces. These will be removed during
+  // Available (cached) back buffer surfaces. These will be cleared during
   // present and replaced by current frong surfaces.
-  NSMutableArray<FlutterSurface*>* _backBufferSurfaces;
+  FlutterBackBufferCache* _backBufferCache;
 
   // Surfaces that currently obtained through backBufferForSize waiting to be
   // presented. This is used to keep the surface alive because the non compositor
@@ -46,14 +104,30 @@ - (instancetype)initWithDevice:(id<MTLDevice>)device
     _containingLayer = containingLayer;
     _delegate = delegate;
 
-    _backBufferSurfaces = [NSMutableArray array];
+    _backBufferCache = [[FlutterBackBufferCache alloc] init];
     _borrowedSurfaces = [NSMutableArray array];
     _frontSurfaces = [NSMutableArray array];
     _layers = [NSMutableArray array];
   }
   return self;
 }
 
+- (FlutterBackBufferCache*)backBufferCache {
+  return _backBufferCache;
+}
+
+- (NSArray*)borrowedSurfaces {
+  return _borrowedSurfaces;
+}
+
+- (NSArray*)frontSurfaces {
+  return _frontSurfaces;
+}
+
+- (NSArray*)layers {
+  return _layers;
+}
+
 - (FlutterSurface*)lookupSurface:(nonnull const FlutterMetalTexture*)texture {
   for (FlutterSurface* surface in _borrowedSurfaces) {
     if (surface.textureId == texture->texture_id) {
@@ -64,14 +138,7 @@ - (FlutterSurface*)lookupSurface:(nonnull const FlutterMetalTexture*)texture {
 }
 
 - (FlutterSurface*)backBufferForSize:(CGSize)size {
-  FlutterSurface* res = nil;
-  for (FlutterSurface* surface in _backBufferSurfaces) {
-    if (CGSizeEqualToSize(surface.size, size)) {
-      res = surface;
-      [_backBufferSurfaces removeObject:surface];
-      break;
-    }
-  }
+  FlutterSurface* res = [_backBufferCache getSurfaceForSize:size];
   if (res == nil) {
     res = [[FlutterSurface alloc] initWithSize:size device:_device];
   }
@@ -85,8 +152,7 @@ - (void)commit:(NSArray<FlutterSurfacePresentInfo*>*)surfaces {
   [_borrowedSurfaces removeAllObjects];
 
   // Release all unused back buffer surfaces and replace them with front surfaces.
-  [_backBufferSurfaces removeAllObjects];
-  [_backBufferSurfaces addObjectsFromArray:_frontSurfaces];
+  [_backBufferCache replaceWith:_frontSurfaces];
 
   // Front surfaces will be replaced by currently presented surfaces.
   [_frontSurfaces removeAllObjects];

shell/platform/darwin/macos/framework/Source/FlutterSurfaceManager_Internal.h

@@ -6,14 +6,31 @@
 
 #import <QuartzCore/QuartzCore.h>
 
+/**
+ * Responsible for caching back buffers to prevent unnecessary IOSurface allocations.
+ */
+@interface FlutterBackBufferCache : NSObject
+
+/**
+ * Removes surface with given size from cache (if available) and returns it.
+ */
+- (nullable FlutterSurface*)getSurfaceForSize:(CGSize)size;
+
+/**
+ * Removes all cached surface replacing them with new ones.
+ */
+- (void)replaceWith:(nonnull NSArray<FlutterSurface*>*)surfaces;
+
+@end
+
 /**
  * Interface to internal properties used for testing.
  */
 @interface FlutterSurfaceManager ()
 
-@property(readonly, nonatomic) NSArray<FlutterSurface*>* backBufferSurfaces;
-@property(readonly, nonatomic) NSArray<FlutterSurface*>* borrowedSurfaces;
-@property(readonly, nonatomic) NSArray<FlutterSurface*>* frontSurfaces;
-@property(readonly, nonatomic) NSArray<CALayer*>* layers;
+@property(readonly, nonatomic, nonnull) FlutterBackBufferCache* backBufferCache;
+@property(readonly, nonatomic, nonnull) NSArray<FlutterSurface*>* borrowedSurfaces;
+@property(readonly, nonatomic, nonnull) NSArray<FlutterSurface*>* frontSurfaces;
+@property(readonly, nonatomic, nonnull) NSArray<CALayer*>* layers;
 
 @end