android - 使用改造和 kotlin channel 实现长轮询

Question

我正在尝试实现生命周期感知的长轮询(在 Activity/fragment 中)。轮询的范围将限于每隔固定时间间隔向服务器发送 API 请求的 fragment 。但是，我无法实现它。

这就是我希望实现的样子

• Have a hard timeout on client-side without considering any extra delay incurred in receiving the response.
• Wait for the response of previous API call before sending the next request. i.e., the request in polling queue should wait for response irrespective of its priority due to polling interval

考虑:

HARD_TIMEOUT = 10 秒

POLLING_INTERVAL = 2s

 Request 1: Started at: 0sec      Response delay:1.2sec   Duration left: 0.8sec
 Request 2: Started at: 2sec      Response delay:0.4sec   Duration left: 1.6sec
 Request 3: Started at: 4sec      Response delay:2.5sec   Duration left: 0sec
 Request 4: Started at: 6.5sec    Response delay:0.5sec   Duration left: 1.0sec
 Request 5: Started at: 8sec      Response delay:0.8sec   Duration left: 1.2sec

对于这个用例，我想使用轮询而不是套接字。任何想法/解决方案将不胜感激。谢谢你。

Answer 1

好的，想出了一个使用 channel 进行轮询的解决方案。这应该可以帮助某人搜索示例。

    private val pollingChannel = Channel<Deferred<Result<OrderStatus>>>()
    val POLLING_TIMEOUT_DURATION = 10000L
    val POLLING_FREQUENCY = 2000L

A channel is required to hold your asynchronous request just in case more request comes in while your async task is being executed.

    val pollingChannel = Channel<Deferred<Pair<Int,Int>>>()

QUEUE EXECUTOR: It will pick an async task and start executing them in FIFO order.

    CoroutineScope(Dispatchers.IO).launch {
        for (i in pollingChannel) {
            val x = i.await()
            println("${SimpleDateFormat("mm:ss.SSS").format(Calendar.getInstance().time)} Request ${x.first}: value ${x.second}")
        }
    }

POLLING FUNCTION: Adds your async task to the polling channel every fixed interval of time until timeout.

    CoroutineScope(Dispatchers.IO).launch {
        var reqIndex = 1
        val timedOut = withTimeoutOrNull(POLLING_TIMEOUT_DURATION) {
            while (receiverJob.isActive) {
                pollingChannel.send(async {
                    getRandomNumber(reqIndex++)
                })
                delay(POLLING_FREQUENCY)
            }
        }
    }

ASYNCHRONOUS OPERATION

为避免回答冗长，我创建了一个随机延迟的函数，请替换为所需的 API 调用

   private suspend fun getRandomNumber(index: Int): Pair<Int,Int> {
    val randomDuration = (1..6L).random() * 500
    delay(randomDuration)
    return Pair(index,(0..100).random())
}

样本输出