Test for reproducing a deadlock between "cancel" and "connectionDidFinishLoading"

DeadlockTest.swift

    func testSDWebImageDownloaderOperationThreadSafety() {
        NSURLProtocol.registerClass(WMFHTTPHangingProtocol)
        defer {
            NSURLProtocol.unregisterClass(WMFHTTPHangingProtocol)
        }

        [0...1000].forEach { _ in
            let downloadOperation = SDWebImageDownloaderOperation(
                request: NSURLRequest(URL: NSURL(string: "https://test.org/foo")!),
                options: [],
                progress: nil,
                completed: nil,
                cancelled: nil
            )

            let testThread = NSThread(target: downloadOperation, selector: Selector("start"), object: nil)
            testThread.start()

            expect(downloadOperation.executing).toEventually(beTrue())
            expect(downloadOperation.finished).toEventually(beFalse())
            expect(downloadOperation.valueForKey("thread") as? NSThread).toEventually(beIdenticalTo(testThread))

            let operations: [() -> Void] = [
                downloadOperation.cancel, {
                downloadOperation.performSelector(
                    Selector("connectionDidFinishLoading:"),
                    onThread: testThread,
                    withObject: nil,
                    waitUntilDone: false)
            }]

            dispatch_apply(2, dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0)) {
                operations[$0]()
            }
            
            expect(downloadOperation.executing).toEventually(beFalse())
        }
    }