fix(ios): synchronize RNSentryTimeToDisplay across main and bridge th… (#5887)

* fix(ios): synchronize RNSentryTimeToDisplay across main and bridge threads

putTimeToInitialDisplayForActiveSpan runs on the main thread from
SentryFramesTracker/CADisplayLink while setActiveSpanId and pop run from the
RN bridge (often off the main thread). Guard static activeSpanId and TTD
caches with @synchronized, copy span ids on set, and factor put logic into
putTimeToDisplayForLocked to avoid nested @synchronized on the same object.

Fixes crashes (EXC_BAD_ACCESS in stringByAppendingString:) from torn reads /
use-after-free and unsafe concurrent NSMutableDictionary access.

* chore: clang format

---------

Co-authored-by: Antonis Lilis <antonis.lilis@sentry.io>

Author: huextrat

CHANGELOG.md

@@ -6,6 +6,12 @@
 > make sure you follow our [migration guide](https://docs.sentry.io/platforms/react-native/migration/) first.
 <!-- prettier-ignore-end -->
 
+## Unreleased
+
+### Fixes
+
+- Fix iOS crash (EXC_BAD_ACCESS) in time-to-initial-display when navigating between screens ([#5887](https://github.com/getsentry/sentry-react-native/pull/5887))
+
 ## 8.6.0
 
 ### Fixes

packages/core/ios/RNSentryTimeToDisplay.m

@@ -2,6 +2,8 @@
 #import <QuartzCore/QuartzCore.h>
 #import <React/RCTLog.h>
 
+// All static state below is accessed from the main thread (CADisplayLink, UI) and from the
+// React Native bridge / JS thread (setActiveSpanId, pop). Synchronize every access.
 @implementation RNSentryTimeToDisplay {
     CADisplayLink *displayLink;
     RCTResponseSenderBlock resolveBlock;
@@ -13,6 +15,37 @@ @implementation RNSentryTimeToDisplay {
 
 static NSString *activeSpanId;
 
++ (void)putTimeToDisplayForLocked:(NSString *)screenId value:(NSNumber *)value
+{
+    if (!screenId) {
+        return;
+    }
+
+    // If key already exists, just update the value,
+    // this should never happen as TTD is recorded once per navigation
+    // We avoid updating the age to avoid the age array shift
+    if ([screenIdToRenderDuration objectForKey:screenId]) {
+        [screenIdToRenderDuration setObject:value forKey:screenId];
+        return;
+    }
+
+    // If we haven't reached capacity yet, just append
+    if (screenIdAge.count < TIME_TO_DISPLAY_ENTRIES_MAX_SIZE) {
+        [screenIdToRenderDuration setObject:value forKey:screenId];
+        [screenIdAge addObject:screenId];
+    } else {
+        // Remove oldest entry, in most case will already be removed by pop
+        NSString *oldestKey = screenIdAge[screenIdCurrentIndex];
+        [screenIdToRenderDuration removeObjectForKey:oldestKey];
+
+        [screenIdToRenderDuration setObject:value forKey:screenId];
+        screenIdAge[screenIdCurrentIndex] = screenId;
+
+        // Update circular index, point to the new oldest
+        screenIdCurrentIndex = (screenIdCurrentIndex + 1) % TIME_TO_DISPLAY_ENTRIES_MAX_SIZE;
+    }
+}
+
 + (void)initialize
 {
     if (self == [RNSentryTimeToDisplay class]) {
@@ -27,51 +60,34 @@ + (void)initialize
 
 + (void)setActiveSpanId:(NSString *)spanId
 {
-    activeSpanId = spanId;
+    @synchronized([RNSentryTimeToDisplay class]) {
+        activeSpanId = spanId != nil ? [spanId copy] : nil;
+    }
 }
 
 + (NSNumber *)popTimeToDisplayFor:(NSString *)screenId
 {
-    NSNumber *value = screenIdToRenderDuration[screenId];
-    [screenIdToRenderDuration removeObjectForKey:screenId];
-    return value;
+    @synchronized([RNSentryTimeToDisplay class]) {
+        NSNumber *value = screenIdToRenderDuration[screenId];
+        [screenIdToRenderDuration removeObjectForKey:screenId];
+        return value;
+    }
 }
 
 + (void)putTimeToInitialDisplayForActiveSpan:(NSNumber *)value
 {
-    if (activeSpanId != nil) {
-        NSString *prefixedSpanId = [@"ttid-navigation-" stringByAppendingString:activeSpanId];
-        [self putTimeToDisplayFor:prefixedSpanId value:value];
+    @synchronized([RNSentryTimeToDisplay class]) {
+        if (activeSpanId != nil) {
+            NSString *prefixedSpanId = [@"ttid-navigation-" stringByAppendingString:activeSpanId];
+            [self putTimeToDisplayForLocked:prefixedSpanId value:value];
+        }
     }
 }
 
 + (void)putTimeToDisplayFor:(NSString *)screenId value:(NSNumber *)value
 {
-    if (!screenId)
-        return;
-
-    // If key already exists, just update the value,
-    // this should never happen as TTD is recorded once per navigation
-    // We avoid updating the age to avoid the age array shift
-    if ([screenIdToRenderDuration objectForKey:screenId]) {
-        [screenIdToRenderDuration setObject:value forKey:screenId];
-        return;
-    }
-
-    // If we haven't reached capacity yet, just append
-    if (screenIdAge.count < TIME_TO_DISPLAY_ENTRIES_MAX_SIZE) {
-        [screenIdToRenderDuration setObject:value forKey:screenId];
-        [screenIdAge addObject:screenId];
-    } else {
-        // Remove oldest entry, in most case will already be removed by pop
-        NSString *oldestKey = screenIdAge[screenIdCurrentIndex];
-        [screenIdToRenderDuration removeObjectForKey:oldestKey];
-
-        [screenIdToRenderDuration setObject:value forKey:screenId];
-        screenIdAge[screenIdCurrentIndex] = screenId;
-
-        // Update circular index, point to the new oldest
-        screenIdCurrentIndex = (screenIdCurrentIndex + 1) % TIME_TO_DISPLAY_ENTRIES_MAX_SIZE;
+    @synchronized([RNSentryTimeToDisplay class]) {
+        [self putTimeToDisplayForLocked:screenId value:value];
     }
 }