fix: Updating AppHang state on main thread (#2793)

Move updating the app hang state to a background thread for anrStopped.

Fixes GH-2791

CHANGELOG.md

@@ -1,5 +1,11 @@
 # Changelog
 
+## Unreleased
+
+### Fixes
+
+- Updating AppHang state on main thread (#2793)
+
 ## 8.3.1
 
 ### Fixes 

Samples/iOS-Swift/iOS-Swift/ViewController.swift

@@ -251,18 +251,31 @@ class ViewController: UIViewController {
     @IBAction func anrFillingRunLoop(_ sender: Any) {
         let buttonTitle = self.anrFillingRunLoopButton.currentTitle
         var i = 0
+
+        func sleep(timeout: Double) {
+            let group = DispatchGroup()
+            group.enter()
+            let queue = DispatchQueue(label: "delay", qos: .background, attributes: [])
+
+            queue.asyncAfter(deadline: .now() + timeout) {
+                group.leave()
+            }
+
+            group.wait()
+        }
 
         dispatchQueue.async {
-            for _ in 0...100_000 {
+            for _ in 0...30 {
                 i += Int.random(in: 0...10)
                 i -= 1
 
                 DispatchQueue.main.async {
-                    self.anrFillingRunLoopButton.setTitle("Work in Progress \(i)", for: .normal)
+                    sleep(timeout: 0.1)
+                    self.anrFillingRunLoopButton.setTitle("Title \(i)", for: .normal)
                 }
             }
 
-            DispatchQueue.main.async {
+            DispatchQueue.main.sync {
                 self.anrFillingRunLoopButton.setTitle(buttonTitle, for: .normal)
             }
         }

SentryTestUtils/TestSentryDispatchQueueWrapper.swift

@@ -9,7 +9,7 @@ public class TestSentryDispatchQueueWrapper: SentryDispatchQueueWrapper {
     /// - SeeAlso: `delayDispatches`, which controls whether the block should execute immediately or with the requested delay.
     public var dispatchAfterExecutesBlock = false
 
-    var dispatchAsyncInvocations = Invocations<() -> Void>()
+    public var dispatchAsyncInvocations = Invocations<() -> Void>()
     public var dispatchAsyncExecutesBlock = true
     public override func dispatchAsync(_ block: @escaping () -> Void) {
         dispatchAsyncCalled += 1

Sources/Sentry/SentryANRTracker.m

@@ -89,7 +89,13 @@ - (void)detectANRs
 
             if (reported) {
                 SENTRY_LOG_WARN(@"ANR stopped.");
-                [self ANRStopped];
+
+                // The ANR stopped, don't block the main thread with calling ANRStopped listeners.
+                // While the ANR code reports an ANR and collects the stack trace, the ANR might
+                // stop simultaneously. In that case, the ANRs stack trace would contain the
+                // following code running on the main thread. To avoid this, we offload work to a
+                // background thread.
+                [self.dispatchQueueWrapper dispatchAsyncWithBlock:^{ [self ANRStopped]; }];
             }
 
             reported = NO;

Sources/Sentry/include/SentryANRTracker.h

@@ -39,6 +39,9 @@ SENTRY_NO_INIT
 
 @end
 
+/**
+ * The ``SentryANRTracker`` calls the methods from background threads.
+ */
 @protocol SentryANRTrackerDelegate <NSObject>
 
 - (void)anrDetected;

Tests/SentryTests/Integrations/ANR/SentryANRTrackerTests.swift

@@ -90,8 +90,9 @@ class SentryANRTrackerTests: XCTestCase, SentryANRTrackerDelegate {
 
     func testMultipleANRs_MultipleReported() {
         anrDetectedExpectation.expectedFulfillmentCount = 3
+        let expectedANRStoppedInvocations = 2
         anrStoppedExpectation.isInverted = false
-        anrStoppedExpectation.expectedFulfillmentCount = 2
+        anrStoppedExpectation.expectedFulfillmentCount = expectedANRStoppedInvocations
 
         fixture.dispatchQueue.blockBeforeMainBlock = {
             self.advanceTime(bySeconds: self.fixture.timeoutInterval)
@@ -105,6 +106,7 @@ class SentryANRTrackerTests: XCTestCase, SentryANRTrackerDelegate {
         start()
 
         wait(for: [anrDetectedExpectation, anrStoppedExpectation], timeout: waitTimeout)
+        XCTAssertEqual(expectedANRStoppedInvocations, fixture.dispatchQueue.dispatchAsyncInvocations.count)
     }
 
     func testAppSuspended_NoANR() {