SentryDependencyContainer.init uses UIApplication.sharedApplication

[philipphofmann]

Description

The SentryDependencyContainer.init can be called from a background thread. Before #5900 this was not problem, but since then the SentryDependencyContainer.initialize calls [[SentryDependencyContainer alloc] init]

sentry-cocoa/Sources/Sentry/SentryDependencyContainer.m

Lines 77 to 88 in d8ceea3

	+ (void)initialize
	{
	if (self == [SentryDependencyContainer class]) {
	// We use two locks, because we don't want the dependencies to block the instance lock.
	// Using two locks speeds up the accessing the dependencies around 5%, which is worth having
	// the extra lock. Measured with self.measure in unit tests.
	sentryDependencyContainerInstanceLock = [[NSObject alloc] init];
	sentryDependencyContainerDependenciesLock = [[NSObject alloc] init];
	instance = [[SentryDependencyContainer alloc] init];
	}
	}

The init method uses the UIApplication.sharedApplication here

sentry-cocoa/Sources/Sentry/SentryDependencyContainer.m

Line 154 in d8ceea3

_application = UIApplication.sharedApplication;

If somebody calls SenrySDK.start from a BG thread, we access the SentryDependencyContainer.initialize also on a BG thread.

sentry-cocoa/Sources/Sentry/SentrySDKInternal.m

Lines 229 to 239 in d8ceea3

	+ (void)startWithOptions:(SentryOptions *)options
	{
	// We save the options before checking for Xcode preview because
	// we will use this options in the preview
	startOption = options;
	if ([SentryDependencyContainer.sharedInstance.processInfoWrapper
	.environment[SENTRY_XCODE_PREVIEW_ENVIRONMENT_KEY] isEqualToString:@"1"]) {
	// Using NSLog because SentryLog was not initialized yet.
	NSLog(@"[SENTRY] [WARNING] SentrySDK not started. Running from Xcode preview.");
	return;
	}

Test to reproduce

func testStartSDK_BGThread() {

    let expectation = self.expectation(description: "Start on background thread")

    DispatchQueue.global().async {
        SentrySDK.start { options in
            options.dsn = "whatever"
        }

        expectation.fulfill()
    }

    wait(for: [expectation], timeout: 5.0)
}

Xcode stacktrace

[linear]

COCOA-718 SentryDependencyContainer.init uses UIApplication.sharedApplication

[kahest]

@philprime did bisect and found that #5900 is the culprit