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Channel (pub sub ) in swift
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public class Channel<Message: Equatable>: IsChannel { | |
private var subscriptions = ThreadSafeArray<Subscription>() | |
public func broadcast(_ message: Message) { | |
subscriptions.forEach { $0.trigger(message: message) } | |
} | |
public func subscribe(_ object: AnyObject, | |
for specificMessage: Message, | |
on queue: DispatchQueue? = nil, | |
callback: @escaping () -> Void) { | |
let filteredCallback = { (message: Message) in | |
if message == specificMessage { callback() } | |
} | |
subscriptions.append(Subscription(object: object, callback: filteredCallback, queue: queue)) | |
} | |
public func subscribe(object: AnyObject, callback: @escaping (Message) -> Void) { | |
subscriptions.append(Subscription(object: object, callback: callback, queue: nil)) | |
} | |
public func unbscribe(object: AnyObject) { | |
subscriptions.remove(where: { $0.object === object }) | |
} | |
private struct Subscription { | |
weak var object: AnyObject? | |
let callback: (Message) -> Void | |
let queue: DispatchQueue? | |
init(object: AnyObject?, callback: @escaping (Message) -> Void, queue: DispatchQueue?) { | |
self.object = object | |
self.callback = callback | |
self.queue = queue | |
} | |
func trigger(message: Message) { | |
// Make sure object is still alive | |
if object == nil { return } | |
if let q = queue { | |
q.async { if self.object != nil { self.callback(message) } } | |
} else { | |
callback(message) | |
} | |
} | |
} | |
} |
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/// This encapsulates a thread safe array protected by its own Dispatch queue. | |
/// The queue is concurrent to allow for concurrent reads but writes are made | |
/// with the `barrier` flag so that only one write operation can happen at a time. | |
/// The write operations wait for pending reads to ficnish and new reads wait for the current | |
/// write operation to finish. | |
class ThreadSafeArray<T> { | |
private let queue = DispatchQueue(label: "com.freshOS.channel.threadSafeArray", attributes: .concurrent) | |
private var underlyingArray: [T] | |
init() { self.underlyingArray = [T]() } | |
func forEach(block: (T) -> Void) { | |
queue.sync { underlyingArray.forEach(block) } | |
} | |
public func append(_ newElement: T) { | |
threadSafeWrite { $0.append(newElement) } | |
} | |
public func remove(where clause: @escaping (T) -> Bool) { | |
threadSafeWrite { if let index = $0.index(where: clause) { $0.remove(at: index) } } | |
} | |
private func threadSafeWrite(callback:@escaping (inout [T]) -> Void) { | |
queue.async(flags: .barrier) { [weak self] in | |
if let strongSelf = self { callback(&strongSelf.underlyingArray) } | |
} | |
} | |
} |
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// Create a channel | |
let chan = Channel<String>() | |
// Receive all messages | |
chan.subscribe(object: self) { message in | |
print(message) | |
} | |
// Receive specific messages on a certain thread | |
chan.subscribe(self, for: "Hello", on: .main) { | |
print("received Hello") | |
} | |
// Send Message | |
chan.broadcast("Hello") | |
// Stop listening | |
chan.unbscribe(object: self) |
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