掛起IO函式永不回傳-有解無憂

我在為 Android 撰寫 UDP 訊息接收回圈時遇到困難。

在下面的代碼中receiveLoop，呼叫receiveMessages從不回傳，因此我從不進入訊息處理回圈。請注意，我仍然能夠接收資料包，但是當通道緩沖區已滿時它會停止。

我希望receiveMessages立即回傳，而其中的阻塞 IO 回圈仍將永遠運行。

class MySocketUDP(private val params: SocketParams) {


    private val rcvSocket: DatagramSocket by lazy {
        val sock = DatagramSocket(params.rcvPort)
        sock.reuseAddress = true
        sock.soTimeout = 1000
        sock
    }

    suspend fun receiveMessages(channel: SendChannel<Message>) {
        withContext(Dispatchers.IO) {
            val buf = ByteArray(MAX_MSG_SIZE)
            while (true) {
                val pkt = DatagramPacket(buf, buf.size)
                try {
                    if (channel.isClosedForSend) {
                        break
                    }
                    rcvSocket.receive(pkt)
                    val msg = packetToMessage(buf, 0, pkt.length)
                    Log.d("SOCKET", "filling channel with $msg")
                    channel.send(msg)
                } catch (ex: SocketTimeoutException) {
                } catch (ex: CancellationException) {
                    break
                }
            }
        }
    }
}

class MyModel {

    private suspend fun receiveLoop(socket: MySocketUDP) {
        withContext(Dispatchers.Main) {
            val channel = Channel<Message>(16)
            socket.receiveMessages(channel)
            Log.d("MODEL", "Entering msg loop")
            for (msg in channel) {
                dispatchRcvMessage(msg)
            }
        }
    }

}

為什么receiveMessages在IO調度程式中運行并從Main調度程式呼叫時永遠不會回傳？
我真的需要為這樣的生產者/消費者作業產生一個執行緒嗎？
你能展示如何以“協程友好”的方式很好地實作這么長的阻塞代碼嗎？

謝謝

uj5u.com熱心網友回復：

receiveMessages()是一個掛起函式，它呼叫另一個掛起函式withContext()，而后者又是一個無限回圈。因此，呼叫socket.receiveMessages(channel)將在回圈未完成時暫停代碼執行。
您需要為消費者和生產者啟動單獨的協程，例如使用launch函式。

使用協程的一些示例：

 val someScope = CoroutineScope(Dispatchers.Main)

 private suspend fun receiveLoop(socket: MySocketUDP) = someScope.launch {
     val channel = Channel<Message>(16)
     socket.receiveMessages(channel)
     Log.d("MODEL", "Entering msg loop")
     for (msg in channel) {
         dispatchRcvMessage(msg)
     }
 }

 // In MySocketUDP
 suspend fun receiveMessages(channel: SendChannel<Message>) {
     someAnotherScope.launch { // or can use coroutineScope builder function
         val buf = ByteArray(MAX_MSG_SIZE)
         while (true) {
             val pkt = DatagramPacket(buf, buf.size)
             try {
                 if (channel.isClosedForSend) {
                     break
                 }
                 rcvSocket.receive(pkt)
                 val msg = packetToMessage(buf, 0, pkt.length)
                 Log.d("SOCKET", "filling channel with $msg")
                 channel.send(msg)
             } catch (ex: SocketTimeoutException) {
             } catch (ex: CancellationException) {
                 break
             }
         }
     }
 }

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標籤：安卓科特林 kotlin 协程阻塞协程作用域

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