fix: App hang with race condition for tick counter (#3290)

Thread sanitizer was complaining about a race condition in the ANR tracker. Added atomic operations to avoid the race condition
getsentry · Oct 4, 2023 · 3f6c30b · 3f6c30b
1 parent f1a6589
commit 3f6c30b
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Showing 3 changed files with 9 additions and 6 deletions.
diff --git a/CHANGELOG.md b/CHANGELOG.md
@@ -4,6 +4,7 @@
 
 ### Fixes
 
+- App hang with race condition for tick counter (#3290)
 - Remove "duplicate library" warning (#3312)
 
 ## 8.13.0

diff --git a/Sources/Sentry/SentryANRTracker.m b/Sources/Sentry/SentryANRTracker.m
@@ -5,6 +5,7 @@
 #import "SentryDispatchQueueWrapper.h"
 #import "SentryLog.h"
 #import "SentryThreadWrapper.h"
+#import <stdatomic.h>
 
 NS_ASSUME_NONNULL_BEGIN
 
@@ -64,7 +65,7 @@ - (void)detectANRs
         state = kSentryANRTrackerRunning;
     }
 
-    __block NSInteger ticksSinceUiUpdate = 0;
+    __block atomic_int ticksSinceUiUpdate = 0;
     __block BOOL reported = NO;
 
     NSInteger reportThreshold = 5;
@@ -81,10 +82,10 @@ - (void)detectANRs
         NSDate *blockDeadline = [[SentryDependencyContainer.sharedInstance.dateProvider date]
             dateByAddingTimeInterval:self.timeoutInterval];
 
-        ticksSinceUiUpdate++;
+        atomic_fetch_add_explicit(&ticksSinceUiUpdate, 1, memory_order_relaxed);
 
         [self.dispatchQueueWrapper dispatchAsyncOnMainQueue:^{
-            ticksSinceUiUpdate = 0;
+            atomic_store_explicit(&ticksSinceUiUpdate, 0, memory_order_relaxed);
 
             if (reported) {
                 SENTRY_LOG_WARN(@"ANR stopped.");
@@ -115,7 +116,8 @@ - (void)detectANRs
             continue;
         }
 
-        if (ticksSinceUiUpdate >= reportThreshold && !reported) {
+        if (atomic_load_explicit(&ticksSinceUiUpdate, memory_order_relaxed) >= reportThreshold
+            && !reported) {
             reported = YES;
 
             if (![self.crashWrapper isApplicationInForeground]) {

diff --git a/Tests/SentryTests/PrivateSentrySDKOnlyTests.swift b/Tests/SentryTests/PrivateSentrySDKOnlyTests.swift
@@ -124,7 +124,7 @@ class PrivateSentrySDKOnlyTests: XCTestCase {
     /**
       * Smoke Tests profiling via PrivateSentrySDKOnly. Actual profiling unit tests are done elsewhere.
      */
-    func testProfilingStartAndCollect() {
+    func testProfilingStartAndCollect() throws {
         let options = Options()
         options.dsn = TestConstants.dsnAsString(username: "SentryFramesTrackingIntegrationTests")
         let client = TestClient(options: options)
@@ -148,7 +148,7 @@ class PrivateSentrySDKOnlyTests: XCTestCase {
         XCTAssertNotNil(profile?["frames"])
         let transactionInfo = payload?["transaction"] as? NSDictionary
         XCTAssertNotNil(transactionInfo)
-        XCTAssertGreaterThan(transactionInfo?["active_thread_id"] as! Int64, 0)
+        XCTAssertGreaterThan(try XCTUnwrap(transactionInfo?["active_thread_id"] as? Int64), 0)
     }
 
     func testProfilingDiscard() {