fix: Crash for Call Should be on Main Thread

CHANGELOG.md

@@ -1,5 +1,9 @@
 # Changelog
 
+## Unreleased
+
+- fix: Crash for Call Should be on Main Thread (#1371)
+
 ## 7.4.3
 
 - fix: Crash for Custom ViewController init on iOS 15 (#1361)

Samples/iOS-ObjectiveC/iOS-ObjectiveC.xcodeproj/project.pbxproj

@@ -17,6 +17,7 @@
 		637AFDDC243B036D0034958B /* main.m in Sources */ = {isa = PBXBuildFile; fileRef = 637AFDDB243B036D0034958B /* main.m */; };
 		7B3427FB25876DDC00056519 /* Tongariro.jpg in Resources */ = {isa = PBXBuildFile; fileRef = 7B3427F925876DDB00056519 /* Tongariro.jpg */; };
 		7B64387A26A6C69F000D0F65 /* LaunchUITests.swift in Sources */ = {isa = PBXBuildFile; fileRef = 7B64387926A6C69F000D0F65 /* LaunchUITests.swift */; };
+		7B8A5C9E2715B5DE008ACD3B /* InitializerViewController.m in Sources */ = {isa = PBXBuildFile; fileRef = 7B8A5C9D2715B5DE008ACD3B /* InitializerViewController.m */; };
 /* End PBXBuildFile section */
 
 /* Begin PBXContainerItemProxy section */
@@ -81,6 +82,8 @@
 		7B64387726A6C69F000D0F65 /* iOS-ObjectiveCUITests.xctest */ = {isa = PBXFileReference; explicitFileType = wrapper.cfbundle; includeInIndex = 0; path = "iOS-ObjectiveCUITests.xctest"; sourceTree = BUILT_PRODUCTS_DIR; };
 		7B64387926A6C69F000D0F65 /* LaunchUITests.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = LaunchUITests.swift; sourceTree = "<group>"; };
 		7B64387B26A6C69F000D0F65 /* Info.plist */ = {isa = PBXFileReference; lastKnownFileType = text.plist.xml; path = Info.plist; sourceTree = "<group>"; };
+		7B8A5C9C2715B5CF008ACD3B /* InitializerViewController.h */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.c.h; path = InitializerViewController.h; sourceTree = "<group>"; };
+		7B8A5C9D2715B5DE008ACD3B /* InitializerViewController.m */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.c.objc; path = InitializerViewController.m; sourceTree = "<group>"; };
 /* End PBXFileReference section */
 
 /* Begin PBXFrameworksBuildPhase section */
@@ -146,6 +149,8 @@
 				637AFDCA243B036B0034958B /* AppDelegate.m */,
 				637AFDCF243B036B0034958B /* ViewController.h */,
 				637AFDD0243B036B0034958B /* ViewController.m */,
+				7B8A5C9C2715B5CF008ACD3B /* InitializerViewController.h */,
+				7B8A5C9D2715B5DE008ACD3B /* InitializerViewController.m */,
 				637AFDD2243B036B0034958B /* Main.storyboard */,
 				637AFDD5243B036D0034958B /* Assets.xcassets */,
 				7B3427F925876DDB00056519 /* Tongariro.jpg */,
@@ -293,6 +298,7 @@
 			buildActionMask = 2147483647;
 			files = (
 				637AFDD1243B036B0034958B /* ViewController.m in Sources */,
+				7B8A5C9E2715B5DE008ACD3B /* InitializerViewController.m in Sources */,
 				637AFDCB243B036B0034958B /* AppDelegate.m in Sources */,
 				637AFDDC243B036D0034958B /* main.m in Sources */,
 			);

Samples/iOS-ObjectiveC/iOS-ObjectiveC/InitializerViewController.h

@@ -0,0 +1,11 @@
+#import <UIKit/UIKit.h>
+
+/**
+ * An empty ViewController to ensure the swizzling of the SentrySDK doesn't call the initialize
+ * method from a background thread. The initializer method is called before the runtime sends its
+ * first message to the class, which is also the case when swizzling a class. For more information
+ * checkout SentryUIViewControllerSwizziling.
+ */
+@interface InitializerViewController : UIViewController
+
+@end

Samples/iOS-ObjectiveC/iOS-ObjectiveC/InitializerViewController.m

@@ -0,0 +1,11 @@
+#import "InitializerViewController.h"
+#import <Foundation/Foundation.h>
+
+@implementation InitializerViewController
+
++ (void)initialize
+{
+    NSAssert([NSThread isMainThread], @"Initializer must only be called from the main thread.");
+}
+
+@end

Sentry.xcodeproj/project.pbxproj

@@ -439,9 +439,6 @@
 		7BECF42826145CD900D9826E /* SentryMechanismMeta.m in Sources */ = {isa = PBXBuildFile; fileRef = 7BECF42726145CD900D9826E /* SentryMechanismMeta.m */; };
 		7BECF432261463E600D9826E /* SentryMechanismMetaTests.swift in Sources */ = {isa = PBXBuildFile; fileRef = 7BECF431261463E600D9826E /* SentryMechanismMetaTests.swift */; };
 		7BED3576266F7BFF00EAA70D /* TestSentryCrashAdapter.m in Sources */ = {isa = PBXBuildFile; fileRef = 7BED3575266F7BFF00EAA70D /* TestSentryCrashAdapter.m */; };
-		7BEF4951270C3F5700F8F30E /* SentrySubClassFinder.h in Headers */ = {isa = PBXBuildFile; fileRef = 7BEF4950270C3F5700F8F30E /* SentrySubClassFinder.h */; };
-		7BEF4953270C3F7F00F8F30E /* SentrySubClassFinder.m in Sources */ = {isa = PBXBuildFile; fileRef = 7BEF4952270C3F7F00F8F30E /* SentrySubClassFinder.m */; };
-		7BEF4955270C3FEC00F8F30E /* SentrySubClassFinderTests.swift in Sources */ = {isa = PBXBuildFile; fileRef = 7BEF4954270C3FEC00F8F30E /* SentrySubClassFinderTests.swift */; };
 		7BEF4957270C4B9D00F8F30E /* SentryUIViewControllerSwizzlingTests.swift in Sources */ = {isa = PBXBuildFile; fileRef = 7BEF4956270C4B9D00F8F30E /* SentryUIViewControllerSwizzlingTests.swift */; };
 		7BEFB044270B0F630025F808 /* SentryTracerObjCTests.m in Sources */ = {isa = PBXBuildFile; fileRef = 7BEFB043270B0F630025F808 /* SentryTracerObjCTests.m */; };
 		7BF536D124BDF3E7004FA6A2 /* SentryEnvelopeTests.swift in Sources */ = {isa = PBXBuildFile; fileRef = 7BF536D024BDF3E7004FA6A2 /* SentryEnvelopeTests.swift */; };
@@ -1006,9 +1003,6 @@
 		7BECF431261463E600D9826E /* SentryMechanismMetaTests.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = SentryMechanismMetaTests.swift; sourceTree = "<group>"; };
 		7BED3574266F7BC600EAA70D /* TestSentryCrashAdapter.h */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.c.h; path = TestSentryCrashAdapter.h; sourceTree = "<group>"; };
 		7BED3575266F7BFF00EAA70D /* TestSentryCrashAdapter.m */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.c.objc; path = TestSentryCrashAdapter.m; sourceTree = "<group>"; };
-		7BEF4950270C3F5700F8F30E /* SentrySubClassFinder.h */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.c.h; path = SentrySubClassFinder.h; sourceTree = "<group>"; };
-		7BEF4952270C3F7F00F8F30E /* SentrySubClassFinder.m */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.c.objc; path = SentrySubClassFinder.m; sourceTree = "<group>"; };
-		7BEF4954270C3FEC00F8F30E /* SentrySubClassFinderTests.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = SentrySubClassFinderTests.swift; sourceTree = "<group>"; };
 		7BEF4956270C4B9D00F8F30E /* SentryUIViewControllerSwizzlingTests.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = SentryUIViewControllerSwizzlingTests.swift; sourceTree = "<group>"; };
 		7BEFB043270B0F630025F808 /* SentryTracerObjCTests.m */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.c.objc; path = SentryTracerObjCTests.m; sourceTree = "<group>"; };
 		7BF536D024BDF3E7004FA6A2 /* SentryEnvelopeTests.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = SentryEnvelopeTests.swift; sourceTree = "<group>"; };
@@ -1427,8 +1421,6 @@
 				7B98D7E725FB7BCD00C5A389 /* SentryAppState.m */,
 				7BD86EC4264A63F6005439DB /* SentrySysctl.h */,
 				7BD86EC6264A641D005439DB /* SentrySysctl.m */,
-				7BEF4950270C3F5700F8F30E /* SentrySubClassFinder.h */,
-				7BEF4952270C3F7F00F8F30E /* SentrySubClassFinder.m */,
 			);
 			name = Helper;
 			sourceTree = "<group>";
@@ -1975,7 +1967,6 @@
 				69BEE6F62620729E006DF9DF /* UrlSessionDelegateSpy.swift */,
 				7BD86ECA264A6DB5005439DB /* TestSysctl.swift */,
 				7B16FD012654F86B008177D3 /* SentrySysctlTests.swift */,
-				7BEF4954270C3FEC00F8F30E /* SentrySubClassFinderTests.swift */,
 			);
 			path = Helper;
 			sourceTree = "<group>";
@@ -2254,7 +2245,6 @@
 				7B04A9AF24EAC02C00E710B1 /* SentryRetryAfterHeaderParser.h in Headers */,
 				7DC83100239826280043DD9A /* SentryIntegrationProtocol.h in Headers */,
 				7B98D7BC25FB607300C5A389 /* SentryOutOfMemoryTracker.h in Headers */,
-				7BEF4951270C3F5700F8F30E /* SentrySubClassFinder.h in Headers */,
 				7BA61CB9247BC57B00C130A8 /* SentryCrashDefaultBinaryImageProvider.h in Headers */,
 				8E4E7C7D25DAB287006AB9E2 /* SentryTracer.h in Headers */,
 				7BC8523724588115005A70F0 /* SentryRateLimitCategory.h in Headers */,
@@ -2417,7 +2407,6 @@
 				15360CD62432832400112302 /* SentryAutoSessionTrackingIntegration.m in Sources */,
 				7BE3C7692445C1A800A38442 /* SentryCurrentDate.m in Sources */,
 				63EED6C02237923600E02400 /* SentryOptions.m in Sources */,
-				7BEF4953270C3F7F00F8F30E /* SentrySubClassFinder.m in Sources */,
 				63AA769E1EB9C57A00D153DE /* SentryError.m in Sources */,
 				7B8713B026415B22006D6004 /* SentryAppStartTrackingIntegration.m in Sources */,
 				8E133FA225E72DEF00ABD0BF /* SentrySamplingContext.m in Sources */,
@@ -2582,7 +2571,6 @@
 				63FE720D20DA66EC00CDBAE8 /* NSError+SimpleConstructor_Tests.m in Sources */,
 				69BEE6F72620729E006DF9DF /* UrlSessionDelegateSpy.swift in Sources */,
 				7B98D7EC25FB7C4900C5A389 /* SentryAppStateTests.swift in Sources */,
-				7BEF4955270C3FEC00F8F30E /* SentrySubClassFinderTests.swift in Sources */,
 				8EE017A126704CD500470616 /* SentryUIPerformanceTrackerTests.swift in Sources */,
 				7B5B94352657AD21002E474B /* SentryFramesTrackingIntegrationTests.swift in Sources */,
 				7BAF3DC8243DB90E008A5414 /* TestTransport.swift in Sources */,

Sources/Sentry/SentryDispatchQueueWrapper.m

@@ -39,6 +39,15 @@ - (void)dispatchAsyncWithBlock:(void (^)(void))block
     });
 }
 
+- (void)dispatchOnMainQueue:(void (^)(void))block
+{
+    dispatch_async(dispatch_get_main_queue(), ^{
+        @autoreleasepool {
+            block();
+        }
+    });
+}
+
 - (void)dispatchOnce:(dispatch_once_t *)predicate block:(void (^)(void))block
 {
     dispatch_once(predicate, block);

Sources/Sentry/SentryUIViewControllerSwizziling.m

@@ -1,7 +1,6 @@
 #import "SentryUIViewControllerSwizziling.h"
 #import "SentryLog.h"
 #import "SentryPerformanceTracker.h"
-#import "SentrySubClassFinder.h"
 #import "SentrySwizzle.h"
 #import "SentryUIViewControllerPerformanceTracker.h"
 #import <SentryDispatchQueueWrapper.h>
@@ -25,25 +24,71 @@ + (void)startWithOptions:(SentryOptions *)options
 
     [SentryUIViewControllerSwizziling swizzleRootViewController];
 
-    // Swizzle all custom UIViewControllers. First, fetch all subclasses of UIViewController and
-    // then swizzle them. As there is no straightforward way to get all sub-classes in Objective-C,
-    // the code first retrieves all classes in the runtime, iterates over all classes, and checks
-    // for every class if UIViewController is a parent. Cause loading all classes can take a few
-    // milliseconds, do this on a background thread, which should be fine because the SDK swizzles
-    // the root view controller and its children above. Previously, the code intercepted the
-    // ViewController initializers with swizzling to swizzle the lifecycle methods. This approach
-    // led to UIViewControllers crashing when using a convenience initializer, see GH-1355. The
-    // error occurred because our swizzling logic adds the method to swizzle if the class doesn't
-    // implement it. It seems like adding an extra initializer causes problems with the rules for
-    // initialization in Swift, see
-    // https://docs.swift.org/swift-book/LanguageGuide/Initialization.html#ID216.
+    [SentryUIViewControllerSwizziling
+        swizzleSubclassesOf:[UIViewController class]
+              dispatchQueue:dispatchQueue
+               swizzleBlock:^(Class class) {
+                   [SentryUIViewControllerSwizziling swizzleViewControllerSubClass:class];
+               }];
+}
 
+/**
+ * To be able to test this we put the logic in a extra method.
+ *
+ * Swizzle all custom UIViewControllers. First, fetch all subclasses of UIViewController and then
+ * swizzle them. As there is no straightforward way to get all sub-classes in Objective-C, the code
+ * first retrieves all classes in the runtime, iterates over all classes, and checks for every class
+ * if UIViewController is a parent. Cause loading all classes can take a few milliseconds, do this
+ * on a background thread, which should be fine because the SDK swizzles the root view controller
+ * and its children above. After finding all subclasses of the UIViewController, this method
+ * swizzles them on the main thread. Swizzling the UIViewControllers on a background thread led to
+ * crashes, see GH-1366.
+ *
+ * Previously, the code intercepted the ViewController initializers with
+ * swizzling to swizzle the lifecycle methods. This approach led to UIViewControllers crashing when
+ * using a convenience initializer, see GH-1355. The error occurred because our swizzling logic adds
+ * the method to swizzle if the class doesn't implement it. It seems like adding an extra
+ * initializer causes problems with the rules for initialization in Swift, see
+ * https://docs.swift.org/swift-book/LanguageGuide/Initialization.html#ID216.
+ */
++ (void)swizzleSubclassesOf:(Class)parentClass
+              dispatchQueue:(SentryDispatchQueueWrapper *)dispatchQueue
+               swizzleBlock:(void (^)(Class))block
+{
     [dispatchQueue dispatchAsyncWithBlock:^{
-        NSArray<Class> *viewControllers =
-            [SentrySubClassFinder getSubclassesOf:[UIViewController class]];
-        for (Class viewController in viewControllers) {
-            [SentryUIViewControllerSwizziling swizzleViewControllerSubClass:viewController];
+        int numClasses = objc_getClassList(NULL, 0);
+        Class *classes = (__unsafe_unretained Class *)malloc(sizeof(Class) * numClasses);
+        numClasses = objc_getClassList(classes, numClasses);
+
+        if (numClasses <= 0) {
+            [SentryLog logWithMessage:@"No classes found when retrieving class list."
+                             andLevel:kSentryLevelError];
         }
+
+        // Storing the actual classes in an NSArray would call initialize of the class, which we
+        // must avoid as we are on a background thread here and dealing with UIViewControllers,
+        // which assume they are running on the main thread. Therefore, we store the indexes instead
+        // so we can search for the subclasses on a background thread.
+        NSMutableArray *indexesToSwizzle = [NSMutableArray new];
+        for (NSInteger i = 0; i < numClasses; i++) {
+            Class superClass = classes[i];
+            do {
+                superClass = class_getSuperclass(superClass);
+            } while (superClass && superClass != parentClass);
+
+            if (superClass != nil) {
+                [indexesToSwizzle addObject:@(i)];
+            }
+        }
+
+        // We must swizzle the UIViewControllers on the main thread. Otherwise, we could crash.
+        [dispatchQueue dispatchOnMainQueue:^{
+            for (NSNumber *i in indexesToSwizzle) {
+                NSInteger index = [i integerValue];
+                block(classes[index]);
+            }
+            free(classes);
+        }];
     }];
 }
 

Sources/Sentry/include/SentryDispatchQueueWrapper.h

@@ -11,6 +11,8 @@ NS_ASSUME_NONNULL_BEGIN
 
 - (void)dispatchAsyncWithBlock:(void (^)(void))block;
 
+- (void)dispatchOnMainQueue:(void (^)(void))block;
+
 - (void)dispatchOnce:(dispatch_once_t *)predicate block:(void (^)(void))block;
 
 @end

Tests/SentryTests/Integrations/SentryUIViewControllerSwizziling+Test.h

@@ -10,6 +10,10 @@ NS_ASSUME_NONNULL_BEGIN
 
 + (void)swizzleViewControllerSubClass:(Class)class;
 
++ (void)swizzleSubclassesOf:(Class)parentClass
+              dispatchQueue:(SentryDispatchQueueWrapper *)dispatchQueue
+               swizzleBlock:(void (^)(Class))block;
+
 @end
 
 #endif