ThreadSafeCollection.swift

import Foundation

final class ThreadSafeCollection<T> {
    private let _lock = NSRecursiveLock()
    private var _observers: [Int: T] = [:]
    private var _nextKey = 0

    func insert(_ observer: T) -> Int {
        _lock.lock()
        defer {
            _lock.unlock()
        }
        let key = _nextKey
        _observers[key] = observer
        _nextKey = key + 1
        return key
    }

    func remove(forKey key: Int) {
        _lock.lock()
        defer {
            _lock.unlock()
        }
        _observers.removeValue(forKey: key)
    }
}

extension ThreadSafeCollection: Sequence {
    func makeIterator() -> DictionaryIterator<Int, T> {
        return _observers.makeIterator()
    }
}