ref: Improve frames tracker performance (#4469)

Improves the speed of the frames tracker by not locking it anymore since it always run in the main thread.

CHANGELOG.md

@@ -8,6 +8,7 @@
 
 ### Improvements
 
+- Improve frames tracker performance (#4469)
 - Log a warning when dropping envelopes due to rate-limiting (#4463)
 
 ## 8.39.0-beta.1

Sources/Sentry/SentryFramesTracker.m

@@ -256,14 +256,11 @@ - (void)displayLinkCallback
 
 - (void)reportNewFrame
 {
-    NSArray *localListeners;
-    @synchronized(self.listeners) {
-        localListeners = [self.listeners allObjects];
-    }
-
     NSDate *newFrameDate = [self.dateProvider date];
-
-    for (id<SentryFramesTrackerListener> listener in localListeners) {
+    // We need to copy the list because some listeners will remove themselves
+    // from the list during the callback, causing a crash during iteration.
+    NSArray<id<SentryFramesTrackerListener>> *listeners = [self.listeners copy];
+    for (id<SentryFramesTrackerListener> listener in listeners) {
         [listener framesTrackerHasNewFrame:newFrameDate];
     }
 }
@@ -310,17 +307,15 @@ - (SentryFramesDelayResult *)getFramesDelay:(uint64_t)startSystemTimestamp
 
 - (void)addListener:(id<SentryFramesTrackerListener>)listener
 {
-
-    @synchronized(self.listeners) {
-        [self.listeners addObject:listener];
-    }
+    // Adding listeners on the main thread to avoid race condition with new frame callback
+    [self.dispatchQueueWrapper dispatchAsyncOnMainQueue:^{ [self.listeners addObject:listener]; }];
 }
 
 - (void)removeListener:(id<SentryFramesTrackerListener>)listener
 {
-    @synchronized(self.listeners) {
-        [self.listeners removeObject:listener];
-    }
+    // Removing listeners on the main thread to avoid race condition with new frame callback
+    [self.dispatchQueueWrapper
+        dispatchAsyncOnMainQueue:^{ [self.listeners removeObject:listener]; }];
 }
 
 - (void)pause

Tests/SentryTests/Integrations/Performance/FramesTracking/SentryFramesTrackerTests.swift

@@ -24,6 +24,7 @@ class SentryFramesTrackerTests: XCTestCase {
         }
 
         lazy var sut: SentryFramesTracker = SentryFramesTracker(displayLinkWrapper: displayLinkWrapper, dateProvider: dateProvider, dispatchQueueWrapper: SentryDispatchQueueWrapper(), notificationCenter: notificationCenter, keepDelayedFramesDuration: keepDelayedFramesDuration)
+
     }
 
     private var fixture: Fixture!
@@ -602,6 +603,16 @@ class SentryFramesTrackerTests: XCTestCase {
         XCTAssertEqual(listener2.newFrameInvocations.count, 1)
         XCTAssertEqual(listener2.newFrameInvocations.first?.timeIntervalSince1970, expectedFrameDate.timeIntervalSince1970)
     }
+
+    func testListenerAreAddedInMainThread() {
+        let dispatchQueueWrapper = TestSentryDispatchQueueWrapper()
+        let sut = SentryFramesTracker(displayLinkWrapper: fixture.displayLinkWrapper, dateProvider: fixture.dateProvider, dispatchQueueWrapper: dispatchQueueWrapper, notificationCenter: fixture.notificationCenter, keepDelayedFramesDuration: fixture.keepDelayedFramesDuration)
+        let listener = FrameTrackerListener()
+
+        sut.add(listener)
+
+        XCTAssertEqual(dispatchQueueWrapper.blockOnMainInvocations.count, 1)
+    }
 
     func testRemoveListener() {
         let sut = fixture.sut