high cpu usage 80% +

[xtuneecu]

i have noticed that my server keeps consuming cpu and i have found a way how to reproduce it and which thread makes the problem
 [External Call]
System.Threading._IOCompletionCallback.PerformIOCompletionCallback(uint, uint, System.Threading.NativeOverlapped*) 20897 (68.37%) 20897 (68.37%) mscorlib.ni

turns out this thread makes the problem when try to make alot of connections then suddenly closes it
makes a littile app which can connect to the socket and stops it when try to make multi connection then this thread makes cpu spike with no return .
help is needed here

[jchristn]

Hi @xtuneecu please share the code to reproduce.

[xtuneecu]

just find out that the problem happens when a connection is coming then the connection is terminated from the client side the server doesn't do disconnect for these connections when idle time out is not set
if i set idle timeout to 10 sec once connections are disconnected cpu usage return normal
note that i make normal tcp connection not Watson so i guess these connections are not handled to disconnect when it is closed from the client side

[xtuneecu]

using System;
using System.Net.Sockets;
using System.Threading;
using System.Threading.Tasks;
using System.Collections.Generic;
using System.Windows.Forms;

namespace SocketFlooder
{
static class Program
{
[STAThread]
static void Main()
{
Application.EnableVisualStyles();
Application.Run(new FloodForm());
}
}

public class FloodForm : Form
{
    private Button startButton;
    private Button stopButton;
    private Button startWithDelayButton;
    private TextBox portBox;
    private TextBox countBox;
    private Label statusLabel;
    private CancellationTokenSource cts;
    private List<Socket> sockets = new List<Socket>();

    public FloodForm()
    {
        Text = "Socket Flood Debugger";
        Width = 400;
        Height = 220;

        Label portLabel = new Label() { Text = "Port:", Left = 10, Top = 20, Width = 40 };
        portBox = new TextBox() { Left = 60, Top = 20, Width = 100, Text = "8080" };

        Label countLabel = new Label() { Text = "Connections:", Left = 10, Top = 60, Width = 100 };
        countBox = new TextBox() { Left = 110, Top = 60, Width = 100, Text = "1000" };

        startButton = new Button() { Text = "Start", Left = 10, Top = 100, Width = 100 };
        stopButton = new Button() { Text = "Stop", Left = 120, Top = 100, Width = 100, Enabled = false };
        startWithDelayButton = new Button() { Text = "Start with Delay", Left = 230, Top = 100, Width = 130 };

        statusLabel = new Label() { Text = "Idle", Left = 10, Top = 140, Width = 360, Height = 30 };

        startButton.Click += StartButton_Click;
        stopButton.Click += StopButton_Click;
        startWithDelayButton.Click += StartWithDelayButton_Click;

        Controls.Add(portLabel);
        Controls.Add(portBox);
        Controls.Add(countLabel);
        Controls.Add(countBox);
        Controls.Add(startButton);
        Controls.Add(stopButton);
        Controls.Add(startWithDelayButton);
        Controls.Add(statusLabel);
    }

    private async void StartButton_Click(object sender, EventArgs e)
    {
        if (!int.TryParse(portBox.Text, out int port) || port <= 0 || port > 65535)
        {
            MessageBox.Show("Invalid port number.");
            return;
        }

        if (!int.TryParse(countBox.Text, out int connectionCount) || connectionCount <= 0)
        {
            MessageBox.Show("Invalid connection count.");
            return;
        }

        startButton.Enabled = false;
        stopButton.Enabled = true;
        statusLabel.Text = "Starting...";

        cts = new CancellationTokenSource();
        sockets.Clear();

        await Task.Run(() => ConnectSockets(connectionCount, port, cts.Token));
    }

    private void StopButton_Click(object sender, EventArgs e)
    {
        cts?.Cancel();
        foreach (var socket in sockets)
        {
            try { socket.Close(); } catch { }
        }
        sockets.Clear();
        statusLabel.Text = "Stopped.";
        startButton.Enabled = true;
        stopButton.Enabled = false;
    }

    private async void StartWithDelayButton_Click(object sender, EventArgs e)
    {
        if (!int.TryParse(portBox.Text, out int port) || port <= 0 || port > 65535)
        {
            MessageBox.Show("Invalid port number.");
            return;
        }

        if (!int.TryParse(countBox.Text, out int connectionCount) || connectionCount <= 0)
        {
            MessageBox.Show("Invalid connection count.");
            return;
        }

        startButton.Enabled = false;
        startWithDelayButton.Enabled = false;
        stopButton.Enabled = true;
        statusLabel.Text = "Starting with delay...";

        cts = new CancellationTokenSource();
        sockets.Clear();

        await Task.Run(() => ConnectSocketsWithDelay(connectionCount, port, cts.Token));
    }

    private void ConnectSockets(int count, int port, CancellationToken token)
    {
        int connected = 0;
        Parallel.For(0, count, (i, state) =>
        {
            if (token.IsCancellationRequested)
            {
                state.Stop();
                return;
            }

            try
            {
                Socket socket = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);
                socket.Connect("127.0.0.1", 111);


                lock (sockets) { sockets.Add(socket); }
                Interlocked.Increment(ref connected);
            }
            catch { }

            Invoke((Action)(() => statusLabel.Text = $"Connected: {connected}"));
        });

        Invoke((Action)(() =>
        {
            statusLabel.Text = $"Finished. Total connected: {connected}";
            startButton.Enabled = true;
            stopButton.Enabled = false;
        }));
    }

    private void ConnectSocketsWithDelay(int count, int port, CancellationToken token)
    {
        int connected = 0;
        for (int i = 0; i < count; i++)
        {
            if (token.IsCancellationRequested)
                break;
            try
            {
                Socket socket = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);
                socket.Connect("127.0.0.1", 111);
                lock (sockets) { sockets.Add(socket); }
                Interlocked.Increment(ref connected);
            }
            catch { }
            Invoke((Action)(() => statusLabel.Text = $"Connected: {connected}"));
            Thread.Sleep(5000); 
        }
        Invoke((Action)(() =>
        {
            statusLabel.Text = $"Finished. Total connected: {connected}";
            startButton.Enabled = true;
            startWithDelayButton.Enabled = true;
            stopButton.Enabled = false;
        }));
    }
}

}

[xtuneecu]

just make 4 or 5 connections to the server then after 1 or 2 stop it from this tool
if idle time out is not set in server cpu will spike more connections not disconnected means more cpu usage

[xtuneecu]

note set ip and port in code not in ui

[jchristn]

High CPU utilization should be fully expected during connection setup. I don't feel compelled to try to optimize that, the test case is intentionally working to force high CPU utilization.

On this point if idle time out is not set in server cpu will spike more connections not disconnected means more cpu usage are you referring to connecting a client and intentionally not setting a timeout and not disconnecting the client? Each new connection is going to spawn a series of background tasks (such as the DataReceiver) so absolutely there will be more background work as the connection count increases.

[xtuneecu]

the test case is made to discover what is going on because i have this problem in my real server. any way thanks for your attention i will try to solve it my self . wish you a good night