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import Foundation | |
import PromiseKit | |
/// serialize async task execution | |
class TaskQueue { | |
private let queue = DispatchQueue(label: "jp.digital-sensation.TaskQueue") | |
private var tasks: [() -> Promise<Void>] = [] | |
private var running = false | |
func schedule<Result>(task: @escaping () -> Promise<Result>) -> Promise<Result> { | |
let (promise, joint) = Promise<Result>.joint() | |
queue.async { | |
self.tasks.append { | |
let promise = task() | |
promise.join(joint) | |
return promise.asVoid() | |
} | |
self.next() | |
} | |
return promise | |
} | |
private func next() { | |
// must be called on self.queue | |
if running || tasks.count <= 0 { | |
return | |
} | |
let task = tasks.removeFirst() | |
running = true | |
task().always(on: self.queue) { | |
self.running = false | |
self.next() | |
} | |
} | |
} |
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