fix: reportFullyDisplayed data race

Fix a data race when calling reportFullyDisplayed from a background
thread by synchronizing the call to the main queue.

CHANGELOG.md

@@ -6,6 +6,8 @@
 
 - Ignore SentryFramesTracker thread sanitizer data races (#3922)
 - Handle no releaseName in WatchDogTerminationLogic (#3919)
+- Fix data race when calling reportFullyDisplayed from a background thread (#3926)
+
 
 ## 8.25.0
 

Sources/Sentry/SentryTimeToDisplayTracker.m

@@ -3,6 +3,7 @@
 #if SENTRY_HAS_UIKIT
 
 #    import "SentryDependencyContainer.h"
+#    import "SentryDispatchQueueWrapper.h"
 #    import "SentryFramesTracker.h"
 #    import "SentryLog.h"
 #    import "SentryMeasurementValue.h"
@@ -26,6 +27,7 @@
 
 @property (nonatomic, weak) SentrySpan *initialDisplaySpan;
 @property (nonatomic, weak) SentrySpan *fullDisplaySpan;
+@property (nonatomic, strong, readonly) SentryDispatchQueueWrapper *dispatchQueueWrapper;
 
 @end
 
@@ -38,10 +40,12 @@ @implementation SentryTimeToDisplayTracker {
 
 - (instancetype)initForController:(UIViewController *)controller
                waitForFullDisplay:(BOOL)waitForFullDisplay
+             dispatchQueueWrapper:(SentryDispatchQueueWrapper *)dispatchQueueWrapper
 {
     if (self = [super init]) {
         _controllerName = [SwiftDescriptor getObjectClassName:controller];
         _waitForFullDisplay = waitForFullDisplay;
+        _dispatchQueueWrapper = dispatchQueueWrapper;
         _initialDisplayReported = NO;
         _fullyDisplayedReported = NO;
     }
@@ -119,7 +123,9 @@ - (void)reportInitialDisplay
 
 - (void)reportFullyDisplayed
 {
-    _fullyDisplayedReported = YES;
+    // All other accesses to _fullyDisplayedReported run on the main thread.
+    // To avoid using locks, we execute this on the main queue instead.
+    [_dispatchQueueWrapper dispatchOnMainQueue:^{ self->_fullyDisplayedReported = YES; }];
 }
 
 - (void)framesTrackerHasNewFrame:(NSDate *)newFrameDate

Sources/Sentry/SentryUIViewControllerPerformanceTracker.m

@@ -2,6 +2,7 @@
 
 #if SENTRY_HAS_UIKIT
 
+#    import "SentryDependencyContainer.h"
 #    import "SentryHub.h"
 #    import "SentryLog.h"
 #    import "SentryOptions.h"
@@ -23,6 +24,7 @@
 
 @property (nonatomic, strong) SentryPerformanceTracker *tracker;
 @property (nullable, nonatomic, weak) SentryTimeToDisplayTracker *currentTTDTracker;
+@property (nonatomic, strong, readonly) SentryDispatchQueueWrapper *dispatchQueueWrapper;
 
 @end
 
@@ -46,6 +48,7 @@ - (instancetype)init
                                                             inAppExcludes:options.inAppExcludes];
 
         _enableWaitForFullDisplay = NO;
+        _dispatchQueueWrapper = SentryDependencyContainer.sharedInstance.dispatchQueueWrapper;
     }
     return self;
 }
@@ -142,7 +145,8 @@ - (void)createTimeToDisplay:(UIViewController *)controller
 
     SentryTimeToDisplayTracker *ttdTracker =
         [[SentryTimeToDisplayTracker alloc] initForController:controller
-                                           waitForFullDisplay:self.enableWaitForFullDisplay];
+                                           waitForFullDisplay:self.enableWaitForFullDisplay
+                                         dispatchQueueWrapper:_dispatchQueueWrapper];
 
     objc_setAssociatedObject(controller, &SENTRY_UI_PERFORMANCE_TRACKER_TTD_TRACKER, ttdTracker,
         OBJC_ASSOCIATION_ASSIGN);

Sources/Sentry/include/SentryTimeToDisplayTracker.h

@@ -4,6 +4,7 @@
 
 @class SentrySpan;
 @class SentryTracer;
+@class SentryDispatchQueueWrapper;
 @class UIViewController;
 
 NS_ASSUME_NONNULL_BEGIN
@@ -25,7 +26,8 @@ SENTRY_NO_INIT
 @property (nonatomic, readonly) BOOL waitForFullDisplay;
 
 - (instancetype)initForController:(UIViewController *)controller
-               waitForFullDisplay:(BOOL)waitForFullDisplay;
+               waitForFullDisplay:(BOOL)waitForFullDisplay
+             dispatchQueueWrapper:(SentryDispatchQueueWrapper *)dispatchQueueWrapper;
 
 - (void)startForTracer:(SentryTracer *)tracer;
 

Tests/SentryTests/Integrations/Performance/UIViewController/SentryTimeToDisplayTrackerTest.swift

@@ -22,7 +22,7 @@ class SentryTimeToDisplayTrackerTest: XCTestCase {
         }
 
         func getSut(for controller: UIViewController, waitForFullDisplay: Bool) -> SentryTimeToDisplayTracker {
-            return SentryTimeToDisplayTracker(for: controller, waitForFullDisplay: waitForFullDisplay)
+            return SentryTimeToDisplayTracker(for: controller, waitForFullDisplay: waitForFullDisplay, dispatchQueueWrapper: SentryDispatchQueueWrapper())
         }
 
         func getTracer() throws -> SentryTracer {
@@ -282,6 +282,18 @@ class SentryTimeToDisplayTrackerTest: XCTestCase {
         assertMeasurement(tracer: tracer, name: "time_to_full_display", duration: 1_000)
     }
 
+    func testReportFullyDisplayed_GetsDispatchedOnMainQueue() {
+        let dispatchQueueWrapper = TestSentryDispatchQueueWrapper()
+
+        let sut = SentryTimeToDisplayTracker(for: UIViewController(), waitForFullDisplay: true, dispatchQueueWrapper: dispatchQueueWrapper)
+
+        let invocationsBefore = dispatchQueueWrapper.blockOnMainInvocations.count
+        sut.reportFullyDisplayed()
+
+        let expectedInvocations = invocationsBefore + 1
+        expect(dispatchQueueWrapper.blockOnMainInvocations.count).to(equal(expectedInvocations), description: "reportFullyDisplayed should be dispatched on the main queue. ")
+    }
+
     func testNotWaitingForFullyDisplayed_AfterTracerTimesOut() throws {
         fixture.dateProvider.setDate(date: Date(timeIntervalSince1970: 9))
 

Tests/SentryTests/SentryHubTests.swift

@@ -1233,7 +1233,7 @@ class SentryHubTests: XCTestCase {
 class TestTimeToDisplayTracker: SentryTimeToDisplayTracker {
 
     init() {
-        super.init(for: UIViewController(), waitForFullDisplay: false)
+        super.init(for: UIViewController(), waitForFullDisplay: false, dispatchQueueWrapper: SentryDispatchQueueWrapper())
     }
 
     var registerFullDisplayCalled = false