swift实现阻塞队列

import Foundation

//阻塞队列
class BlockingQueue<T>{
    
    private var queue : [T]
    private let capacity : Int
    private let queueAccess = DispatchQueue(label: "BlockingQueue.queueAccess")
    private let emptySemaphore : DispatchSemaphore
    private let fullSemaphore : DispatchSemaphore
    
    init(_ capacity : Int) {
        self.queue = []
        self.capacity = capacity
        self.emptySemaphore = DispatchSemaphore(value: 0)
        self.fullSemaphore = DispatchSemaphore(value: capacity)
    }
    
    //放入一个元素
    func put(_ element : T){
        fullSemaphore.wait()
        queueAccess.sync {
            self.queue.append(element)
        }
        emptySemaphore.signal()
    }
    
    //取出一个元素
    func take() -> T{
        emptySemaphore.wait()
        let element = queueAccess.sync {
            let item = self.queue.removeFirst()
            return item
        }
        fullSemaphore.signal()
        return element
    }
}