[ASTextKitRenderer] Adding locking when accessing the text renderer c…

…ache (#2075) While NSCache is thread safe, that alone does not make `rendererForAttributes` thread safe. This experiment will add a lock to `rendererForAttributes` to see how that affects performance/stability. As second experiment will forego the cache altogether to validate that we are getting some value out of having a renderer cache.
TextureGroup · Jan 25, 2023 · 2c7ba22 · 2c7ba22
1 parent c989e1a
commit 2c7ba22
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Showing 3 changed files with 24 additions and 2 deletions.
diff --git a/Source/ASExperimentalFeatures.h b/Source/ASExperimentalFeatures.h
@@ -31,6 +31,8 @@ typedef NS_OPTIONS(NSUInteger, ASExperimentalFeatures) {
   ASExperimentalDisableGlobalTextkitLock = 1 << 10,                         // exp_disable_global_textkit_lock
   ASExperimentalMainThreadOnlyDataController = 1 << 11,                     // exp_main_thread_only_data_controller
   ASExperimentalRangeUpdateOnChangesetUpdate = 1 << 12,                     // exp_range_update_on_changeset_update
+  ASExperimentalNoTextRendererCache = 1 << 13,                              // exp_no_text_renderer_cache
+  ASExperimentalLockTextRendererCache = 1 << 14,                            // exp_lock_text_renderer_cache
   ASExperimentalFeatureAll = 0xFFFFFFFF
 };
 

diff --git a/Source/ASExperimentalFeatures.mm b/Source/ASExperimentalFeatures.mm
@@ -24,7 +24,10 @@
                                       @"exp_optimize_data_controller_pipeline",
                                       @"exp_disable_global_textkit_lock",
                                       @"exp_main_thread_only_data_controller",
-                                      @"exp_range_update_on_changeset_update"]));
+                                      @"exp_range_update_on_changeset_update",
+                                      @"exp_no_text_renderer_cache",
+                                      @"exp_lock_text_renderer_cache"]));
+
   if (flags == ASExperimentalFeatureAll) {
     return allNames;
   }

diff --git a/Source/ASTextNode.mm b/Source/ASTextNode.mm
@@ -115,7 +115,7 @@ - (BOOL)isEqual:(ASTextNodeRendererKey *)object
  we maintain a LRU renderer cache that is queried via a unique key based on text kit attributes and constrained size. 
  */
 
-static ASTextKitRenderer *rendererForAttributes(ASTextKitAttributes attributes, CGSize constrainedSize)
+static ASTextKitRenderer *_rendererForAttributes(ASTextKitAttributes attributes, CGSize constrainedSize)
 {
   NSCache *cache = sharedRendererCache();
 
@@ -130,6 +130,23 @@ - (BOOL)isEqual:(ASTextNodeRendererKey *)object
   return renderer;
 }
 
+static AS::RecursiveMutex __sharedRendererCacheInstanceLock__;
+
+static ASTextKitRenderer *rendererForAttributes(ASTextKitAttributes attributes, CGSize constrainedSize)
+{
+  BOOL neverCache = ASActivateExperimentalFeature(ASExperimentalNoTextRendererCache);
+  if (neverCache) {
+    return [[ASTextKitRenderer alloc] initWithTextKitAttributes:attributes constrainedSize:constrainedSize];
+  }
+
+  BOOL lockCache = ASActivateExperimentalFeature(ASExperimentalLockTextRendererCache);
+  if (lockCache) {
+    AS::MutexLocker l(__sharedRendererCacheInstanceLock__);
+    return _rendererForAttributes(attributes, constrainedSize);
+  }
+  return _rendererForAttributes(attributes, constrainedSize);
+}
+
 #pragma mark - ASTextNodeDrawParameter
 
 @interface ASTextNodeDrawParameter : NSObject {