fix(session-replay): Use low priority queue for dispatch queue wrapper

CHANGELOG.md

@@ -2,6 +2,10 @@
 
 ## Unreleased
 
+### Fixes
+
+- Uses low-priority queues to reduce the chance of session replay internal multi-threading processes being dropped (#5280)
+
 ### Improvements
 
 - Threading issues in internal dependency container (#5225)

Sources/Sentry/SentryDispatchFactory.m

@@ -11,13 +11,16 @@
     return [[SentryDispatchQueueWrapper alloc] initWithName:name attributes:attributes];
 }
 
-- (SentryDispatchQueueWrapper *)createBackgroundQueueWithName:(const char *)name
-                                             relativePriority:(int)relativePriority
+- (SentryDispatchQueueWrapper *)createLowPriorityQueue:(const char *)name
+                                      relativePriority:(int)relativePriority
 {
     SENTRY_CASSERT(relativePriority <= 0 && relativePriority >= QOS_MIN_RELATIVE_PRIORITY,
         @"Relative priority must be between 0 and %d", QOS_MIN_RELATIVE_PRIORITY);
+    // The QOS_CLASS_UTILITY is defined in `qos.h` and used by the `DISPATCH_QUEUE_PRIORITY_LOW`,
+    // therefore it can be considered it a low priority queue
+    // Reference: https://developer.apple.com/documentation/dispatch/dispatch_queue_priority_low
     dispatch_queue_attr_t attributes = dispatch_queue_attr_make_with_qos_class(
-        DISPATCH_QUEUE_SERIAL, QOS_CLASS_BACKGROUND, relativePriority);
+        DISPATCH_QUEUE_SERIAL, QOS_CLASS_UTILITY, relativePriority);
     return [[SentryDispatchQueueWrapper alloc] initWithName:name attributes:attributes];
 }
 

Sources/Sentry/SentrySessionReplayIntegration.m

@@ -143,14 +143,14 @@
     // The asset worker queue is used to work on video and frames data.
     // Use a relative priority of -1 to make it lower than the default background priority.
     _replayAssetWorkerQueue =
-        [dispatchQueueProvider createBackgroundQueueWithName:"io.sentry.session-replay.asset-worker"
-                                            relativePriority:-1];
+        [dispatchQueueProvider createLowPriorityQueue:"io.sentry.session-replay.asset-worker"
+                                     relativePriority:-1];
     // The dispatch queue is used to asynchronously wait for the asset worker queue to finish its
     // work. To avoid a deadlock, the priority of the processing queue must be lower than the asset
     // worker queue. Use a relative priority of -2 to make it lower than the asset worker queue.
     _replayProcessingQueue =
-        [dispatchQueueProvider createBackgroundQueueWithName:"io.sentry.session-replay.processing"
-                                            relativePriority:-2];
+        [dispatchQueueProvider createLowPriorityQueue:"io.sentry.session-replay.processing"
+                                     relativePriority:-2];
 
     // The asset worker queue is used to work on video and frames data.
 

Sources/Sentry/include/SentryDispatchQueueProviderProtocol.h

@@ -13,7 +13,7 @@ NS_ASSUME_NONNULL_BEGIN
                                    attributes:(dispatch_queue_attr_t)attributes;
 
 /**
- * Creates a background queue with the given name and relative priority, wrapped in a @c
+ * Creates a low priority queue with the given name and relative priority, wrapped in a @c
  * SentryDispatchQueueWrapper.
  *
  * @note This method is only a factory method and does not keep a reference to the created queue.
@@ -25,8 +25,8 @@ NS_ASSUME_NONNULL_BEGIN
  * quality-of-service.
  * @return Unretained reference to the created queue.
  */
-- (SentryDispatchQueueWrapper *)createBackgroundQueueWithName:(const char *)name
-                                             relativePriority:(int)relativePriority;
+- (SentryDispatchQueueWrapper *)createLowPriorityQueue:(const char *)name
+                                      relativePriority:(int)relativePriority;
 
 @end
 

Tests/SentryTests/Integrations/SessionReplay/SentrySessionReplayIntegrationTests.swift

@@ -650,10 +650,10 @@ class SentrySessionReplayIntegrationTests: XCTestCase {
 
         // -- Assert --
         XCTAssertEqual(assetWorkerQueue.queue.label, "io.sentry.session-replay.asset-worker")
-        XCTAssertEqual(assetWorkerQueue.queue.qos.qosClass, .background)
+        XCTAssertEqual(assetWorkerQueue.queue.qos.qosClass, .utility)
 
         XCTAssertEqual(processingQueue.queue.label, "io.sentry.session-replay.processing")
-        XCTAssertEqual(processingQueue.queue.qos.qosClass, .background)
+        XCTAssertEqual(processingQueue.queue.qos.qosClass, .utility)
 
         // The actual priorities are not relevant, we just need to check that the processing queue has a lower priority
         // than the asset worker queue and that both are lower than the default priority.

Tests/SentryTests/Networking/SentryDispatchFactoryTests.m

@@ -43,7 +43,7 @@ - (void)testQueueWithNameAndAttributes_shouldReturnQueueWithNameAndAttributesSet
 }
 
 - (void)
-    testCreateBackgroundQueueWithNameAndRelativePriority_shouldReturnQueueWithNameAndRelativePrioritySet
+    testCreateLowPriorityQueueWithNameAndRelativePriority_shouldReturnQueueWithNameAndRelativePrioritySet
 {
     // Note: We are not testing the functionality of the queue itself, just the creation of it,
     // making sure the factory sets the name and attributes correctly.
@@ -53,8 +53,8 @@ - (void)testQueueWithNameAndAttributes_shouldReturnQueueWithNameAndAttributesSet
     int relativePriority = -5;
 
     // -- Act --
-    SentryDispatchQueueWrapper *wrappedQueue =
-        [self.sut createBackgroundQueueWithName:queueName relativePriority:relativePriority];
+    SentryDispatchQueueWrapper *wrappedQueue = [self.sut createLowPriorityQueue:queueName
+                                                               relativePriority:relativePriority];
 
     // -- Assert --
     const char *actualName = dispatch_queue_get_label(wrappedQueue.queue);
@@ -63,7 +63,7 @@ - (void)testQueueWithNameAndAttributes_shouldReturnQueueWithNameAndAttributesSet
     int actualRelativePriority;
     dispatch_qos_class_t actualQoSClass
         = dispatch_queue_get_qos_class(wrappedQueue.queue, &actualRelativePriority);
-    XCTAssertEqual(actualQoSClass, QOS_CLASS_BACKGROUND);
+    XCTAssertEqual(actualQoSClass, QOS_CLASS_UTILITY);
     XCTAssertEqual(actualRelativePriority, relativePriority);
 }
 
@@ -111,7 +111,7 @@ - (void)testSource_queueUsesCorrectQoSAndPriority
     uint64_t leeway = 0;
     const char *queueName = "sentry-dispatch-factory.qos-check";
     dispatch_queue_attr_t attributes
-        = dispatch_queue_attr_make_with_qos_class(DISPATCH_QUEUE_SERIAL, QOS_CLASS_BACKGROUND, -10);
+        = dispatch_queue_attr_make_with_qos_class(DISPATCH_QUEUE_SERIAL, QOS_CLASS_UTILITY, -10);
     void (^eventHandler)(void) = ^{ };
 
     // -- Act --
@@ -128,7 +128,7 @@ - (void)testSource_queueUsesCorrectQoSAndPriority
 
     int relativePriority;
     dispatch_qos_class_t qos = dispatch_queue_get_qos_class(queueWrapper.queue, &relativePriority);
-    XCTAssertEqual(qos, QOS_CLASS_BACKGROUND);
+    XCTAssertEqual(qos, QOS_CLASS_UTILITY);
     XCTAssertEqual(relativePriority, -10);
 }
 

Tests/SentryTests/Networking/SentryDispatchQueueWrapperTests.m

@@ -29,7 +29,7 @@ - (void)testInitWithNameAndAttributes_customAttributes_shouldCreateQueueWithGive
     // -- Arrange --
     const char *queueName = "sentry-dispatch-factory.test";
     int relativePriority = -5;
-    qos_class_t qosClass = QOS_CLASS_BACKGROUND;
+    qos_class_t qosClass = QOS_CLASS_UTILITY;
     dispatch_queue_attr_t _Nullable attr = DISPATCH_QUEUE_SERIAL;
 
     dispatch_queue_attr_t _Nullable attributes
@@ -43,7 +43,7 @@ - (void)testInitWithNameAndAttributes_customAttributes_shouldCreateQueueWithGive
     int actualRelativePriority;
     dispatch_qos_class_t actualQoSClass
         = dispatch_queue_get_qos_class(wrappedQueue.queue, &actualRelativePriority);
-    XCTAssertEqual(actualQoSClass, QOS_CLASS_BACKGROUND);
+    XCTAssertEqual(actualQoSClass, QOS_CLASS_UTILITY);
     XCTAssertEqual(actualRelativePriority, -5);
 }
 
@@ -58,7 +58,7 @@ - (void)testInitWithNameAndAttributes_customAttributes_shouldCreateQueueWithGive
     // -- Arrange --
     const char *queueName = "sentry-dispatch-factory.test";
     int relativePriority = 5;
-    qos_class_t qosClass = QOS_CLASS_BACKGROUND;
+    qos_class_t qosClass = QOS_CLASS_UTILITY;
     dispatch_queue_attr_t _Nullable attr = DISPATCH_QUEUE_SERIAL;
 
     dispatch_queue_attr_t _Nullable attributes