Synchronized containers deadlock when reading from multiple threads

[dalemyers]

If you try and read a container from multiple threads, even if you've called .synchronize(), you will run into a dead lock issue. The following code is an example:

let container = Container()

_ = container.register(Foo.self) { _ in
    Thread.sleep(forTimeInterval: 100.0)
    return Foo()
}.inObjectScope(.container)

_ = container.register(Bar.self) { _ in
    return Bar()
}.inObjectScope(.container)

DispatchQueue.global().async {
    _ = container.synchronize().resolve(Foo.self)
}

// Allow the dispatch to happen
Thread.sleep(forTimeInterval: 0.5)

// This will block for 100 seconds
_ = container.synchronize().resolve(Bar.self)

The problem stems from the use of NSRecursiveLock. This lock allows multiple read acquisitions on the same thread, but will block across different threads.