[C#] Start, Pause Token , CancelSourceToken trong Task Parallelism

Xin chào các bạn, bài viết hôm nay mình sẽ tiếp tục hướng dẫn các bạn cách Start, Pause, Resume và Stop trong Task Parallel C# Winform.

Trong NetFramework, thì Task có hỗ trợ CancelSourceToken, còn PauseTokenSource thì không có hỗ trợ.

Nên chúng ta cần viết thêm hai class PauseToken và PauseTokenSource.

Giao diện demo ứng dụng Start, Pause, Resume, Stop Task Parallel C#:

1. Tạo Class PauseTokenSource.cs:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading;
using System.Threading.Tasks;

namespace PauseTokenSource
{
    class PauseTokenSource
    {
        private volatile TaskCompletionSource<bool> m_paused;
        internal static readonly Task s_completedTask = Task.FromResult(true);

        public bool IsPaused
        {
            get { return m_paused != null; }
            set
            {
                if (value)
                {
                    Interlocked.CompareExchange(
                        ref m_paused, new TaskCompletionSource<bool>(), null);
                }
                else
                {
                    while (true)
                    {
                        var tcs = m_paused;
                        if (tcs == null) return;
                        if (Interlocked.CompareExchange(ref m_paused, null, tcs) == tcs)
                        {
                            tcs.SetResult(true);
                            break;
                        }
                    }
                }
            }
        }
        public PauseToken Token { get { return new PauseToken(this); } }

        internal Task WaitWhilePausedAsync()
        {
            var cur = m_paused;
            return cur != null ? cur.Task : s_completedTask;
        }
    }
}

2. Tiếp tục tạo thêm Class PauseToken.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace PauseTokenSource
{
    class PauseToken
    {
        private readonly PauseTokenSource m_source;
        internal PauseToken(PauseTokenSource source) { m_source = source; }

        public bool IsPaused { get { return m_source != null && m_source.IsPaused; } }

        public Task WaitWhilePausedAsync()
        {
            return IsPaused ?
                m_source.WaitWhilePausedAsync() :
                PauseTokenSource.s_completedTask;
        }
    }
}

3. Viết code cho Form Main ứng dụng Demo Task C#:

using System;
using System.Threading;
using System.Threading.Tasks;
using System.Windows.Forms;

namespace PauseTokenSource
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }
        PauseTokenSource pts;
        CancellationTokenSource cts;
        private async void btnStart_Click(object sender, EventArgs e)
        {
            btnStart.Enabled = false;
            btnPause.Enabled = true;
            btnStop.Enabled = true;
            rbResult.Clear();
            cts = new CancellationTokenSource();
            pts = new PauseTokenSource();
            var tokenSource = cts.Token;
            await SomeMethodAsync(tokenSource);
        }

        
        public  async Task SomeMethodAsync(CancellationToken ct)
        {
          
            for (int i = 0; i <= 100; i++)
            {                
                this.BeginInvoke(new Action(()=>
                {
                    rbResult.Text += "i = " + i + "\r\n";
                    progressBar1.Value = i;
                    lbl_status.Text = i + "%";
                    if(i == 100)
                    {
                        MessageBox.Show("Finish");
                        btnStart.Enabled = true;
                        btnPause.Enabled = false;
                        btnStop.Enabled = false;
                    }
                }));

                if (ct.IsCancellationRequested)
                {
                    break;
                }
              
                await Task.Delay(200);
                await pts.WaitWhilePausedAsync();
            }
           
        }

        private void btnPause_Click(object sender, EventArgs e)
        {
            pts.IsPaused = !pts.IsPaused;
            if (pts.IsPaused)
            {
                btnPause.Text = "Resume";                
            }
            else
            {
                btnPause.Text = "Pause";
            }
        }

        private void btnStop_Click(object sender, EventArgs e)
        {
            cts.Cancel();
            btnStart.Enabled = true;
            btnPause.Enabled = false;
            btnStop.Enabled = false;
        }
    }
}

Các bạn có thể download source code bên dưới về để tham khảo.

Thanks for watching!

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