fix: Threading issues in binary image cache (#3468)

Add synchronize to start and stop of SentryBinaryImage crash to avoid
threading issues that can lead to crashes.

Fixes GH-3462

CHANGELOG.md

@@ -7,6 +7,7 @@
 
 - Crash when UINavigationController doesn't have rootViewController (#3455)
 - Crash when synchronizing invalid JSON breadcrumbs to SentryWatchdogTermination (#3458)
+- Threading issues in binary image cache (#3468)
 - Finish transaction for external view controllers (#3440)
 
 ## 8.17.0

Sources/Sentry/SentryBinaryImageCache.m

@@ -21,16 +21,20 @@ @implementation SentryBinaryImageCache
 
 - (void)start
 {
-    _cache = [NSMutableArray array];
-    sentrycrashbic_registerAddedCallback(&binaryImageWasAdded);
-    sentrycrashbic_registerRemovedCallback(&binaryImageWasRemoved);
+    @synchronized(self) {
+        _cache = [NSMutableArray array];
+        sentrycrashbic_registerAddedCallback(&binaryImageWasAdded);
+        sentrycrashbic_registerRemovedCallback(&binaryImageWasRemoved);
+    }
 }
 
 - (void)stop
 {
-    sentrycrashbic_registerAddedCallback(NULL);
-    sentrycrashbic_registerRemovedCallback(NULL);
-    _cache = nil;
+    @synchronized(self) {
+        sentrycrashbic_registerAddedCallback(NULL);
+        sentrycrashbic_registerRemovedCallback(NULL);
+        _cache = nil;
+    }
 }
 
 - (void)binaryImageAdded:(const SentryCrashBinaryImage *)image

Tests/SentryTests/SentryBinaryImageCacheTests.swift

@@ -115,6 +115,26 @@ class SentryBinaryImageCacheTests: XCTestCase {
         let didNotFind = sut.pathFor(inAppInclude: "Name at 0")
         expect(didNotFind) == nil
     }
+
+    func testAddingImagesWhileStoppingAndStartingOnDifferentThread() {
+        let count = 1_000
+
+        let expectation = expectation(description: "Add images on background thread")
+        expectation.expectedFulfillmentCount = count
+
+        for i in 0..<count {
+            DispatchQueue.global().async {
+                var binaryImage0 = self.createCrashBinaryImage(UInt(i * 10))
+                self.sut.binaryImageAdded(&binaryImage0)
+
+                self.sut.stop()
+                self.sut.start()
+                expectation.fulfill()
+            }
+        }
+
+        waitForExpectations(timeout: 1)
+    }
 
     func createCrashBinaryImage(_ address: UInt) -> SentryCrashBinaryImage {
         let name = "Expected Name at \(address)"