fix(session-replay): improve multi-threading of session replay processing

CHANGELOG.md

@@ -6,6 +6,7 @@
 
 - Crash in setMeasurement when name is nil (#5064)
 - Make setMeasurement thread safe (#5067, #5078)
+- Fix thread inversion warning in session replay (#5018)
 
 ## 8.49.0
 

Sentry.xcodeproj/project.pbxproj

@@ -835,6 +835,7 @@
 		D4AF00212D2E92FD00F5F3D7 /* SentryNSFileManagerSwizzling.m in Sources */ = {isa = PBXBuildFile; fileRef = D4AF00202D2E92FD00F5F3D7 /* SentryNSFileManagerSwizzling.m */; };
 		D4AF00232D2E931000F5F3D7 /* SentryNSFileManagerSwizzling.h in Headers */ = {isa = PBXBuildFile; fileRef = D4AF00222D2E931000F5F3D7 /* SentryNSFileManagerSwizzling.h */; };
 		D4AF00252D2E93C400F5F3D7 /* SentryNSFileManagerSwizzlingTests.m in Sources */ = {isa = PBXBuildFile; fileRef = D4AF00242D2E93C400F5F3D7 /* SentryNSFileManagerSwizzlingTests.m */; };
+		D4B0DC7F2DA9257A00DE61B6 /* SentryRenderVideoResult.swift in Sources */ = {isa = PBXBuildFile; fileRef = D4B0DC7E2DA9257200DE61B6 /* SentryRenderVideoResult.swift */; };
 		D4C5F59A2D4249E6002A9BF6 /* DataSentryTracingIntegrationTests.swift in Sources */ = {isa = PBXBuildFile; fileRef = D4C5F5992D4249E0002A9BF6 /* DataSentryTracingIntegrationTests.swift */; };
 		D4E3F35D2D4A864600F79E2B /* SentryNSDictionarySanitizeTests.swift in Sources */ = {isa = PBXBuildFile; fileRef = D42E48582D48FC8F00D251BC /* SentryNSDictionarySanitizeTests.swift */; };
 		D4E3F35E2D4A877300F79E2B /* SentryNSDictionarySanitize+Tests.m in Sources */ = {isa = PBXBuildFile; fileRef = D41909942D490006002B83D0 /* SentryNSDictionarySanitize+Tests.m */; };
@@ -2014,6 +2015,7 @@
 		D4AF00202D2E92FD00F5F3D7 /* SentryNSFileManagerSwizzling.m */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.c.objc; path = SentryNSFileManagerSwizzling.m; sourceTree = "<group>"; };
 		D4AF00222D2E931000F5F3D7 /* SentryNSFileManagerSwizzling.h */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.c.h; name = SentryNSFileManagerSwizzling.h; path = include/SentryNSFileManagerSwizzling.h; sourceTree = "<group>"; };
 		D4AF00242D2E93C400F5F3D7 /* SentryNSFileManagerSwizzlingTests.m */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.c.objc; path = SentryNSFileManagerSwizzlingTests.m; sourceTree = "<group>"; };
+		D4B0DC7E2DA9257200DE61B6 /* SentryRenderVideoResult.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = SentryRenderVideoResult.swift; sourceTree = "<group>"; };
 		D4C5F5992D4249E0002A9BF6 /* DataSentryTracingIntegrationTests.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = DataSentryTracingIntegrationTests.swift; sourceTree = "<group>"; };
 		D4E829D12D75E2DE00D375AD /* SentryDefaultViewRenderer.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = SentryDefaultViewRenderer.swift; sourceTree = "<group>"; };
 		D4E829D32D75E34A00D375AD /* SentryExperimentalViewRenderer.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = SentryExperimentalViewRenderer.swift; sourceTree = "<group>"; };
@@ -4269,6 +4271,7 @@
 				D8CAC02A2BA0663E00E38F34 /* SentryReplayOptions.swift */,
 				D8CAC02B2BA0663E00E38F34 /* SentryVideoInfo.swift */,
 				D802994D2BA836EF000F0081 /* SentryOnDemandReplay.swift */,
+				D4B0DC7E2DA9257200DE61B6 /* SentryRenderVideoResult.swift */,
 				D451ED5E2D92ECDE00C9BEA8 /* SentryReplayFrame.swift */,
 				D451ED5C2D92ECD200C9BEA8 /* SentryOnDemandReplayError.swift */,
 				D802994F2BA83A88000F0081 /* SentryPixelBuffer.swift */,
@@ -4959,6 +4962,7 @@
 				7B98D7D325FB65AE00C5A389 /* SentryWatchdogTerminationTracker.m in Sources */,
 				8E564AE8267AF22600FE117D /* SentryNetworkTrackingIntegration.m in Sources */,
 				63AA75EF1EB8B3C400D153DE /* SentryClient.m in Sources */,
+				D4B0DC7F2DA9257A00DE61B6 /* SentryRenderVideoResult.swift in Sources */,
 				7B7D873624864C9D00D2ECFF /* SentryCrashDefaultMachineContextWrapper.m in Sources */,
 				63FE712F20DA4C1100CDBAE8 /* SentryCrashSysCtl.c in Sources */,
 				62212B872D520CB00062C2FA /* SentryEventCodable.swift in Sources */,

Sources/Sentry/SentryDispatchQueueWrapper.m

@@ -105,6 +105,14 @@ - (nullable dispatch_block_t)createDispatchBlock:(void (^)(void))block
     return dispatch_block_create(0, block);
 }
 
++ (SentryDispatchQueueWrapper *)createBackgroundDispatchQueueWithName:(const char *)name
+                                                     relativePriority:(int)relativePriority
+
+{
+    dispatch_queue_attr_t attributes = dispatch_queue_attr_make_with_qos_class(
+        DISPATCH_QUEUE_SERIAL, QOS_CLASS_BACKGROUND, relativePriority);
+    return [[SentryDispatchQueueWrapper alloc] initWithName:name attributes:attributes];
+}
 @end
 
 NS_ASSUME_NONNULL_END

Sources/Sentry/SentrySessionReplayIntegration.m

@@ -58,6 +58,8 @@ @implementation SentrySessionReplayIntegration {
     // replay absolutely needs segment 0 to make replay work.
     BOOL _rateLimited;
     id<SentryCurrentDateProvider> _dateProvider;
+    SentryDispatchQueueWrapper *_replayProcessingQueue;
+    SentryDispatchQueueWrapper *_replayAssetWorkerQueue;
 }
 
 - (instancetype)init
@@ -122,6 +124,19 @@ - (void)setupWith:(SentryReplayOptions *)replayOptions
     }
 
     _notificationCenter = SentryDependencyContainer.sharedInstance.notificationCenterWrapper;
+    _dateProvider = SentryDependencyContainer.sharedInstance.dateProvider;
+
+    // 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 = [SentryDispatchQueueWrapper
+        createBackgroundDispatchQueueWithName:"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 = [SentryDispatchQueueWrapper
+        createBackgroundDispatchQueueWithName:"io.sentry.session-replay.processing"
+                             relativePriority:-2];
 
     // The asset worker queue is used to work on video and frames data.
 
@@ -193,7 +208,10 @@ - (void)resumePreviousSessionReplay:(SentryEvent *)event
     }
 
     SentryOnDemandReplay *resumeReplayMaker =
-        [[SentryOnDemandReplay alloc] initWithContentFrom:lastReplayURL.path];
+        [[SentryOnDemandReplay alloc] initWithContentFrom:lastReplayURL.path
+                                          processingQueue:_replayProcessingQueue
+                                         assetWorkerQueue:_replayAssetWorkerQueue
+                                             dateProvider:_dateProvider];
     resumeReplayMaker.bitRate = _replayOptions.replayBitRate;
     resumeReplayMaker.videoScale = _replayOptions.sizeScale;
 
@@ -205,14 +223,35 @@ - (void)resumePreviousSessionReplay:(SentryEvent *)event
     }
     NSDate *end = [beginning dateByAddingTimeInterval:duration];
 
-    NSError *error;
-    NSArray<SentryVideoInfo *> *videos = [resumeReplayMaker createVideoWithBeginning:beginning
-                                                                                 end:end
-                                                                               error:&error];
-    if (videos == nil) {
+    // This method is called from a background thread, so we can synchronize the creation of the
+    // video with a dispatch group.
+    __block NSArray<SentryVideoInfo *> *videos;
+    __block NSError *_Nullable error;
+
+    dispatch_group_t group = dispatch_group_create();
+    dispatch_group_enter(group);
+    [resumeReplayMaker
+        createVideoAsyncWithBeginning:beginning
+                                  end:end
+                           completion:^(NSArray<SentryVideoInfo *> *_Nullable resultVideos,
+                               NSError *_Nullable resultError) {
+                               videos = resultVideos;
+                               error = resultError;
+                               dispatch_group_leave(group);
+                           }];
+    // Wait for the video creation to finish without a timeout, because the video creation is
+    // expected to finish in a reasonable time frame.
+    dispatch_group_wait(group, DISPATCH_TIME_FOREVER);
+
+    // Either error or videos should be set.
+    if (error != nil) {
         SENTRY_LOG_ERROR(@"Could not create replay video, reason: %@", error);
         return;
     }
+    if (videos == nil) {
+        SENTRY_LOG_ERROR(@"Could not create replay video, reason: no videos available");
+        return;
+    }
 
     // For each segment we need to create a new event with the video.
     int _segmentId = segmentId;
@@ -323,30 +362,27 @@ - (void)startWithOptions:(SentryReplayOptions *)replayOptions
                                                      error:nil];
     }
 
-    SentryOnDemandReplay *replayMaker = [[SentryOnDemandReplay alloc] initWithOutputPath:docs.path];
+    SentryOnDemandReplay *replayMaker =
+        [[SentryOnDemandReplay alloc] initWithOutputPath:docs.path
+                                         processingQueue:_replayProcessingQueue
+                                        assetWorkerQueue:_replayAssetWorkerQueue
+                                            dateProvider:_dateProvider];
     replayMaker.bitRate = replayOptions.replayBitRate;
     replayMaker.videoScale = replayOptions.sizeScale;
     replayMaker.cacheMaxSize
         = (NSInteger)(shouldReplayFullSession ? replayOptions.sessionSegmentDuration + 1
                                               : replayOptions.errorReplayDuration + 1);
 
-    dispatch_queue_attr_t attributes = dispatch_queue_attr_make_with_qos_class(
-        DISPATCH_QUEUE_SERIAL, DISPATCH_QUEUE_PRIORITY_LOW, 0);
-    SentryDispatchQueueWrapper *dispatchQueue =
-        [[SentryDispatchQueueWrapper alloc] initWithName:"io.sentry.session-replay"
-                                              attributes:attributes];
-
-    self.sessionReplay = [[SentrySessionReplay alloc]
-        initWithReplayOptions:replayOptions
-             replayFolderPath:docs
-           screenshotProvider:screenshotProvider
-                  replayMaker:replayMaker
-          breadcrumbConverter:breadcrumbConverter
-                 touchTracker:_touchTracker
-                 dateProvider:SentryDependencyContainer.sharedInstance.dateProvider
-                     delegate:self
-                dispatchQueue:dispatchQueue
-           displayLinkWrapper:[[SentryDisplayLinkWrapper alloc] init]];
+    SentryDisplayLinkWrapper *displayLinkWrapper = [[SentryDisplayLinkWrapper alloc] init];
+    self.sessionReplay = [[SentrySessionReplay alloc] initWithReplayOptions:replayOptions
+                                                           replayFolderPath:docs
+                                                         screenshotProvider:screenshotProvider
+                                                                replayMaker:replayMaker
+                                                        breadcrumbConverter:breadcrumbConverter
+                                                               touchTracker:_touchTracker
+                                                               dateProvider:_dateProvider
+                                                                   delegate:self
+                                                         displayLinkWrapper:displayLinkWrapper];
 
     [self.sessionReplay
         startWithRootView:SentryDependencyContainer.sharedInstance.application.windows.firstObject

Sources/Sentry/include/SentryDispatchQueueWrapper.h

@@ -32,6 +32,8 @@ NS_ASSUME_NONNULL_BEGIN
 
 - (nullable dispatch_block_t)createDispatchBlock:(void (^)(void))block;
 
++ (SentryDispatchQueueWrapper *)createBackgroundDispatchQueueWithName:(const char *)name
+                                                     relativePriority:(int)relativePriority;
 @end
 
 NS_ASSUME_NONNULL_END