iOS异步变成同步

有些时候会有一些特殊的需求，让一些异步 *** 作变成同步，我记录了如下的几种方式，备用：

func oneAsynTask(callback: @escaping (Int)->Void) {
        DispatchQueue.global().async {
            print("task running")
            sleep(5)
            callback(5)
            print("task finsh")
        }
    }

way1

  func waitToFinishWay1() {
       /// 信号量实现
        DispatchQueue.global().async {
            let semp = DispatchSemaphore(value: 0)
            var returnValue: Int = 0
            self.oneAsynTask { value in
                returnValue = value
                semp.signal()
            }
            print("waiting ...")
            semp.wait()
            print("waiting finsh")
            print("returnValue:\(returnValue)")
        }
    }

way2

func waitToFinishWay2() {
    DispatchQueue.global().async {
        var returnValue: Int = 0
        let condition = NSCondition()
        condition.lock()
        self.oneAsynTask { value in
            returnValue = value
            condition.signal()
        }
        print("waiting ...")
        while returnValue == 0 { // 加这个，是为了可能还没有开始等待，上面的异步任务已经完成
            condition.wait()
        }
        
        condition.unlock()
        print("waiting finsh")
        print("returnValue:\(returnValue)")
    }
}

way3

func waitTOFinishWay3() {
    DispatchQueue.global().async {
        var returnValue: Int = 0
        let group = DispatchGroup()
        group.enter()
        self.oneAsynTask { value in
            returnValue = value
            group.leave()
        }
        print("waiting ...")
        group.wait()
        print("waiting finsh")
        print("returnValue:\(returnValue)")
        
    }
}

way4

func waitToFinshWay4() {
    DispatchQueue.global().async {
        var returnValue: Int = 0
        let group = DispatchGroup()
        group.enter()
        self.oneAsynTask { value in
            returnValue = value
            group.leave()
        }
        print("waiting ...")
        while returnValue == 0 {
            
        }
        print("waiting finsh")
        print("returnValue:\(returnValue)")
        
    }
}