一个 Android 使用 DatagramSocket 发送 UDP 的问题？ https://stackoverflow.com/q/55533832/5105007

https://stackoverflow.com/q/55533832/5105007

class UdpSendActivity : AppCompatActivity() {

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_udp_send)

        Thread(::runTest1).start()
        Thread(::runTest2).start()
    }


    fun runTest1():Unit {
        val dstAddressList = List(50 ){
            Inet4Address.getByName("192.168.1.${10 + it}")
        }

        val srcSocket = DatagramSocket()
        val byteArray = ByteArray(500)

        val startMs = System.currentTimeMillis()
        for (dstAddress in dstAddressList) {
            val packet = DatagramPacket(byteArray, 0, byteArray.size, dstAddress, 55555)

            srcSocket.send(packet)
            srcSocket.send(packet)
            srcSocket.send(packet)
            srcSocket.send(packet)

        }
        val costMs = System.currentTimeMillis() - startMs
        Log.e("UdpSendActivity", "#A $costMs ms")
    }

    fun runTest2():Unit {
        val dstAddressList = List(50 ){
            Inet4Address.getByName("192.168.1.${10 + it}")
        }

//        val srcSocket = DatagramSocket()
        val byteArray = ByteArray(500)
        val startMs = System.currentTimeMillis()

        for (dstAddress in dstAddressList) {
            val packet = DatagramPacket(byteArray, 0, byteArray.size, dstAddress, 55555)
            // the diffrent line
            val srcSocket = DatagramSocket()
            srcSocket.send(packet)
            srcSocket.send(packet)
            srcSocket.send(packet)
            srcSocket.send(packet)
        }
        val costMs = System.currentTimeMillis() - startMs
        Log.e("UdpSendActivity", "#B $costMs ms")
    }
}

log:

E/UdpSendActivity: #B 23 ms
E/UdpSendActivity: #A 1507 ms

两个测试的区别在于使用一个 DatagramSocket 发送给所有的目的地址还是每个目的地址创建一个新的 DatagramSocket 来发送，日志显示前者速度非常慢。