C# Task Cancel 任務取消

作者：貓貓風 ฅ●ω●ฅ│2019-02-04 17:52:34│巴幣：28│人氣：3855

Task 和 Thread 一樣，都是屬於執行緒的一種，Task 和 Thread主要的差異為 Task在多執行緒

的狀態會自動按比例調整，排程，屬於多執行緒特化的一種物件，還資源許多狀態管理

低級別操作，優先全調度等功能

本篇主要是演示，如何在Task運行中進行取消的動作

在建立Task時傳入可隨時處發取消的Token ? 稱做 CancellationToken

並在執行取消命令時送出 Cacel指令，藉此取消 Task的動作

以下為實作程式碼 (此程式不能在Debug模式下執行)

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using System.Threading;
using System.Threading.Tasks;
namespace Task_Status
{
public partial class Form1 : Form
{
public Form1()
{
InitializeComponent();
}
CancellationTokenSource cts = new CancellationTokenSource();
CancellationToken cancelToken;
Thread _monitor_task;
Task<int> t;
bool click = false;
private void Form1_Load(object sender, EventArgs e)
{
cancelToken = cts.Token;
_monitor_task = new Thread(monitor_task);
_monitor_task.Start();
//new task bind with cancel token
//return result use int type
t = new Task<int>(() => AddCancleByThrow(cancelToken), cancelToken);
t.Start();
t.ContinueWith(TaskEndedByCatch); //when task complete run this
}
void monitor_task()
{
while (true)
{
this.Invoke(new Action(() => {
textBox3.Text = t.IsCanceled.ToString();
textBox4.Text = t.IsCompleted.ToString();
textBox5.Text = t.IsFaulted.ToString();
}));
// monitor is cancel ?
if (t.IsCanceled)
{
this.Invoke(new Action(() => {
textBox2.Text = "task Cancel";
}));
t.Dispose();
// t = null;
}
Thread.Sleep(30);
}
}
void TaskEndedByCatch(Task<int> task) //task end do this
{
try
{
this.Invoke(new Action(() => {
// get run result
textBox2.Text = "task Complete: result = "+task.Result ;
button1.Text = "New task";
}));
click = !click;
t.Dispose();
}
catch (AggregateException e)
{
MessageBox.Show(e.ToString());
}
}
int AddCancleByThrow(CancellationToken ct) // running task
{
int result = 0;
this.Invoke(new Action(() =>{
textBox2.Text = "new Task Running";
}));
while (result < 5)
{
if (ct.IsCancellationRequested)
{
ct.ThrowIfCancellationRequested();
}
result++;
this.Invoke(new Action(() =>{
textBox1.Text = result.ToString();
}));
Thread.Sleep(1000);
}
return result;
}
private void button1_Click(object sender, EventArgs e)
{
//wait press to stop
if (!click)
{
cts.Cancel();
button1.Text = "New task";
click = !click;
}
else
{
button1.Text = "Cancel";
click = !click;
textBox2.Text = "new Task Running";
// when start new task
cts = new CancellationTokenSource();
cancelToken = cts.Token;
if (t != null)
{
t = new Task<int>
(() => AddCancleByThrow(cancelToken), cancelToken);
t.Start();
t.ContinueWith(TaskEndedByCatch);
}
}
}
private void Form1_FormClosing(object sender, FormClosingEventArgs e)
{
_monitor_task.Abort();
}
}
}