CODEWITHSUNDEEP
swiftreactive-cocoa
code-ninja-54321
code-ninja-54321

Reputation: 539

Retaining a Signal or SignalProducer?

Is it my responsibility to maintain a reference to a Signal or a SignalProducer, e.g., using an instance variable?

In other words, will they automatically disappear and stop sending events when they get deallocated?

Upvotes: 1

Views: 316

Answers (1)

Qinghua
Qinghua

Reputation: 371

FYI, not necessary, the Signal will be disposed and stop forwarding events.

Signalis a class type, if no one have a reference to it, it should be deinit. However, Signal implementation introduces a tricky way to retain itself, see state property, so that there exists some memory leaks in temporary. As seen in source code, if there have some observers subscribe on the Signal, it's state does retain it in turn until all observers unsubscribed or the Signal received completed/error/interrupted event.

Here some marked code snippets.

// definition of SignalState
private struct SignalState<Value, Error: Swift.Error> {
    var observers: Bag<Signal<Value, Error>.Observer> = Bag()
    var retainedSignal: Signal<Value, Error>?  // here is the key
}

public func observe(_ observer: Observer) -> Disposable? {
    var token: RemovalToken?
    state.modify {
        $0?.retainedSignal = self  // retain self when one observer on
        token = $0?.observers.insert(observer)
    }

    if let token = token {
        return ActionDisposable { [weak self] in
            if let strongSelf = self {
                strongSelf.state.modify { state in
                    state?.observers.remove(using: token)
                    if state?.observers.isEmpty ?? false {
                        // break retain cycle when disposed
                        state!.retainedSignal = nil  
                    }
                }
            }
        }
    } else {
        observer.sendInterrupted()
        return nil
    }
}

How about SignalProducer?
It is really intuitive, SignalProducer is just struct type, and you should not consider its lifetime.

Upvotes: 3

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