1、Task的優勢
ThreadPool相比Thread來說具備了很多優勢，但是ThreadPool卻又存在一些使用上的不友善。比如：
◆ ThreadPool不支援線程的取消、完成、失敗通知等互動性操作；
◆ ThreadPool不支援線程執行的先後次序；
以往，如果開發者要實作上述功能，需要完成很多額外的工作，現在，FCL中提供了一個功能更強大的概念：Task。Task線上程池的基礎上進行了優化，并提供了更多的API。在FCL4.0中，如果我們要編寫多線程程式，Task顯然已經優于傳統的方式。
以下是一個簡單的任務示例：
using System;
using System.Threading;
using System.Threading.Tasks;
namespace ConsoleApp1
{
class Program
{
static void Main(string[] args)
{
Task t = new Task(() =>
{
Console.WriteLine("任務開始工作……");
//模拟工作過程
Thread.Sleep(5000);
});
t.Start();
t.ContinueWith((task) =>
{
Console.WriteLine("任務完成，完成時候的狀态為：");
Console.WriteLine("IsCanceled={0}\tIsCompleted={1}\tIsFaulted={2}", task.IsCanceled, task.IsCompleted, task.IsFaulted);
});
Console.ReadKey();
}
}
}
2、Task的用法
2.1 建立任務
無傳回值的方式
方式1:
var t1 = new Task(() => TaskMethod("Task 1"));
t1.Start();
Task.WaitAll(t1);//等待所有任務結束
注:
任務的狀态:
Start之前為:Created
Start之後為:WaitingToRun
方式2:
方式3:
Task.Factory.StartNew(() => TaskMethod("Task 3")); 直接異步的方法
或者
var t3=Task.Factory.StartNew(() => TaskMethod("Task 3"));
Task.WaitAll(t3);//等待所有任務結束
注:
任務的狀态:
Start之前為:Running
Start之後為:Running
例子：
using System;
using System.Threading;
using System.Threading.Tasks;
namespace ConsoleApp1
{
class Program
{
static void Main(string[] args)
{
var t1 = new Task(() => TaskMethod("Task 1"));
var t2 = new Task(() => TaskMethod("Task 2"));
t2.Start();
t1.Start();
Task.WaitAll(t1, t2);
Task.Run(() => TaskMethod("Task 3"));
Task.Factory.StartNew(() => TaskMethod("Task 4"));
//标記為長時間運作任務,則任務不會使用線程池,而在單獨的線程中運作。
Task.Factory.StartNew(() => TaskMethod("Task 5"), TaskCreationOptions.LongRunning);
#region 正常的使用方式
Console.WriteLine("主線程執行業務處理.");
//建立任務
Task task = new Task(() =>
{
Console.WriteLine("使用System.Threading.Tasks.Task執行異步操作.");
for (int i = 0; i < 10; i++)
{
Console.WriteLine(i);
}
});
//啟動任務,并安排到目前任務隊列線程中執行任務(System.Threading.Tasks.TaskScheduler)
task.Start();
Console.WriteLine("主線程執行其他處理");
task.Wait();
#endregion
Thread.Sleep(TimeSpan.FromSeconds(1));
Console.ReadLine();
}
static void TaskMethod(string name)
{
Console.WriteLine("Task {0} is running on a thread id {1}. Is thread pool thread: {2}",
name, Thread.CurrentThread.ManagedThreadId, Thread.CurrentThread.IsThreadPoolThread);
}
}
}
async/await的實作方式:
using System;
using System.Threading;
using System.Threading.Tasks;
namespace ConsoleApp1
{
class Program
{
async static void AsyncFunction()
{
await Task.Delay(1);
Console.WriteLine("使用System.Threading.Tasks.Task執行異步操作.");
for (int i = 0; i < 10; i++)
{
Console.WriteLine(string.Format("AsyncFunction:i={0}", i));
}
}
public static void Main()
{
Console.WriteLine("主線程執行業務處理.");
AsyncFunction();
Console.WriteLine("主線程執行其他處理");
for (int i = 0; i < 10; i++)
{
Console.WriteLine(string.Format("Main:i={0}", i));
}
Console.ReadLine();
}
}
}
帶傳回值的方式
方式4:
Task<int> task = CreateTask("Task 1");
task.Start();
int result = task.Result;
using System;
using System.Threading;
using System.Threading.Tasks;
namespace ConsoleApp1
{
class Program
{
static Task<int> CreateTask(string name)
{
return new Task<int>(() => TaskMethod(name));
}
static void Main(string[] args)
{
TaskMethod("Main Thread Task");
Task<int> task = CreateTask("Task 1");
task.Start();
int result = task.Result;
Console.WriteLine("Task 1 Result is: {0}", result);
task = CreateTask("Task 2");
//該任務會運作在主線程中
task.RunSynchronously();
result = task.Result;
Console.WriteLine("Task 2 Result is: {0}", result);
task = CreateTask("Task 3");
Console.WriteLine(task.Status);
task.Start();
while (!task.IsCompleted)
{
Console.WriteLine(task.Status);
Thread.Sleep(TimeSpan.FromSeconds(0.5));
}
Console.WriteLine(task.Status);
result = task.Result;
Console.WriteLine("Task 3 Result is: {0}", result);
#region 正常使用方式
//建立任務
Task<int> getsumtask = new Task<int>(() => Getsum());
//啟動任務,并安排到目前任務隊列線程中執行任務(System.Threading.Tasks.TaskScheduler)
getsumtask.Start();
Console.WriteLine("主線程執行其他處理");
//等待任務的完成執行過程。
getsumtask.Wait();
//獲得任務的執行結果
Console.WriteLine("任務執行結果：{0}", getsumtask.Result.ToString());
#endregion
}
static int TaskMethod(string name)
{
Console.WriteLine("Task {0} is running on a thread id {1}. Is thread pool thread: {2}",
name, Thread.CurrentThread.ManagedThreadId, Thread.CurrentThread.IsThreadPoolThread);
Thread.Sleep(TimeSpan.FromSeconds(2));
return 42;
}
static int Getsum()
{
int sum = 0;
Console.WriteLine("使用Task執行異步操作.");
for (int i = 0; i < 100; i++)
{
sum += i;
}
return sum;
}
}
}
async/await的實作:
using System;
using System.Threading.Tasks;
namespace ConsoleApp1
{
class Program
{
public static void Main()
{
var ret1 = AsyncGetsum();
Console.WriteLine("主線程執行其他處理");
for (int i = 1; i <= 3; i++)
Console.WriteLine("Call Main()");
int result = ret1.Result; //阻塞主線程
Console.WriteLine("任務執行結果：{0}", result);
}
async static Task<int> AsyncGetsum()
{
await Task.Delay(1);
int sum = 0;
Console.WriteLine("使用Task執行異步操作.");
for (int i = 0; i < 100; i++)
{
sum += i;
}
return sum;
}
}
}
2.2、組合任務.ContinueWith
簡單Demo:
using System;
using System.Threading.Tasks;
namespace ConsoleApp1
{
class Program
{
public static void Main()
{
//建立一個任務
Task<int> task = new Task<int>(() =>
{
int sum = 0;
Console.WriteLine("使用Task執行異步操作.");
for (int i = 0; i < 100; i++)
{
sum += i;
}
return sum;
});
//啟動任務,并安排到目前任務隊列線程中執行任務(System.Threading.Tasks.TaskScheduler)
task.Start();
Console.WriteLine("主線程執行其他處理");
//任務完成時執行處理。
Task cwt = task.ContinueWith(t =>
{
Console.WriteLine("任務完成後的執行結果：{0}", t.Result.ToString());
});
task.Wait();
cwt.Wait();
}
}
}
任務的串行:
using System;
using System.Collections.Concurrent;
using System.Threading;
using System.Threading.Tasks;
namespace ConsoleApp1
{
class Program
{
static void Main(string[] args)
{
ConcurrentStack<int> stack = new ConcurrentStack<int>();
//t1先串行
var t1 = Task.Factory.StartNew(() =>
{
stack.Push(1);
stack.Push(2);
});
//t2,t3并行執行
var t2 = t1.ContinueWith(t =>
{
int result;
stack.TryPop(out result);
Console.WriteLine("Task t2 result={0},Thread id {1}", result, Thread.CurrentThread.ManagedThreadId);
});
//t2,t3并行執行
var t3 = t1.ContinueWith(t =>
{
int result;
stack.TryPop(out result);
Console.WriteLine("Task t3 result={0},Thread id {1}", result, Thread.CurrentThread.ManagedThreadId);
});
//等待t2和t3執行完
Task.WaitAll(t2, t3);
//t7串行執行
var t4 = Task.Factory.StartNew(() =>
{
Console.WriteLine("目前集合元素個數：{0},Thread id {1}", stack.Count, Thread.CurrentThread.ManagedThreadId);
});
t4.Wait();
}
}
}
子任務:
using System;
using System.Threading.Tasks;
namespace ConsoleApp1
{
class Program
{
public static void Main()
{
Task<string[]> parent = new Task<string[]>(state =>
{
Console.WriteLine(state);
string[] result = new string[2];
//建立并啟動子任務
new Task(() => { result[0] = "我是子任務1。"; }, TaskCreationOptions.AttachedToParent).Start();
new Task(() => { result[1] = "我是子任務2。"; }, TaskCreationOptions.AttachedToParent).Start();
return result;
}, "我是父任務，并在我的處理過程中建立多個子任務，所有子任務完成以後我才會結束執行。");
//任務處理完成後執行的操作
parent.ContinueWith(t =>
{
Array.ForEach(t.Result, r => Console.WriteLine(r));
});
//啟動父任務
parent.Start();
//等待任務結束 Wait隻能等待父線程結束,沒辦法等到父線程的ContinueWith結束
//parent.Wait();
Console.ReadLine();
}
}
}
動态并行(TaskCreationOptions.AttachedToParent) 父任務等待所有子任務完成後 整個任務才算完成
using System;
using System.Threading;
using System.Threading.Tasks;
namespace ConsoleApp1
{
class Node
{
public Node Left { get; set; }
public Node Right { get; set; }
public string Text { get; set; }
}
class Program
{
static Node GetNode()
{
Node root = new Node
{
Left = new Node
{
Left = new Node
{
Text = "L-L"
},
Right = new Node
{
Text = "L-R"
},
Text = "L"
},
Right = new Node
{
Left = new Node
{
Text = "R-L"
},
Right = new Node
{
Text = "R-R"
},
Text = "R"
},
Text = "Root"
};
return root;
}
static void Main(string[] args)
{
Node root = GetNode();
DisplayTree(root);
}
static void DisplayTree(Node root)
{
var task = Task.Factory.StartNew(() => DisplayNode(root),
CancellationToken.None,
TaskCreationOptions.None,
TaskScheduler.Default);
task.Wait();
}
static void DisplayNode(Node current)
{
if (current.Left != null)
Task.Factory.StartNew(() => DisplayNode(current.Left),
CancellationToken.None,
TaskCreationOptions.AttachedToParent,
TaskScheduler.Default);
if (current.Right != null)
Task.Factory.StartNew(() => DisplayNode(current.Right),
CancellationToken.None,
TaskCreationOptions.AttachedToParent,
TaskScheduler.Default);
Console.WriteLine("目前節點的值為{0};處理的ThreadId={1}", current.Text, Thread.CurrentThread.ManagedThreadId);
}
}
}
2.3、取消任務 CancellationTokenSource
using System;
using System.Threading;
using System.Threading.Tasks;
namespace ConsoleApp1
{
class Program
{
private static int TaskMethod(string name, int seconds, CancellationToken token)
{
Console.WriteLine("Task {0} is running on a thread id {1}. Is thread pool thread: {2}",
name, Thread.CurrentThread.ManagedThreadId, Thread.CurrentThread.IsThreadPoolThread);
for (int i = 0; i < seconds; i++)
{
Thread.Sleep(TimeSpan.FromSeconds(1));
if (token.IsCancellationRequested) return -1;
}
return 42 * seconds;
}
private static void Main(string[] args)
{
var cts = new CancellationTokenSource();
var longTask = new Task<int>(() => TaskMethod("Task 1", 10, cts.Token), cts.Token);
Console.WriteLine(longTask.Status);
cts.Cancel();
Console.WriteLine(longTask.Status);
Console.WriteLine("First task has been cancelled before execution");
cts = new CancellationTokenSource();
longTask = new Task<int>(() => TaskMethod("Task 2", 10, cts.Token), cts.Token);
longTask.Start();
for (int i = 0; i < 5; i++)
{
Thread.Sleep(TimeSpan.FromSeconds(0.5));
Console.WriteLine(longTask.Status);
}
cts.Cancel();
for (int i = 0; i < 5; i++)
{
Thread.Sleep(TimeSpan.FromSeconds(0.5));
Console.WriteLine(longTask.Status);
}
Console.WriteLine("A task has been completed with result {0}.", longTask.Result);
}
}
}
2.4、處理任務中的異常
單個任務:
using System;
using System.Threading;
using System.Threading.Tasks;
namespace ConsoleApp1
{
class Program
{
static int TaskMethod(string name, int seconds)
{
Console.WriteLine("Task {0} is running on a thread id {1}. Is thread pool thread: {2}",
name, Thread.CurrentThread.ManagedThreadId, Thread.CurrentThread.IsThreadPoolThread);
Thread.Sleep(TimeSpan.FromSeconds(seconds));
throw new Exception("Boom!");
return 42 * seconds;
}
static void Main(string[] args)
{
try
{
Task<int> task = Task.Run(() => TaskMethod("Task 2", 2));
int result = task.GetAwaiter().GetResult();
Console.WriteLine("Result: {0}", result);
}
catch (Exception ex)
{
Console.WriteLine("Task 2 Exception caught: {0}", ex.Message);
}
Console.WriteLine("----------------------------------------------");
Console.WriteLine();
}
}
}
多個任務:
using System;using System.Threading;using System.Threading.Tasks;namespace ConsoleApp1
{ class Program
{ static int TaskMethod(string name, int seconds)
{
Console.WriteLine("Task {0} is running on a thread id {1}. Is thread pool thread: {2}",
name, Thread.CurrentThread.ManagedThreadId, Thread.CurrentThread.IsThreadPoolThread);
Thread.Sleep(TimeSpan.FromSeconds(seconds)); throw new Exception(string.Format("Task {0} Boom!", name)); return 42 * seconds;
} public static void Main(string[] args)
{ try
{ var t1 = new Task<int>(() => TaskMethod("Task 3", 3)); var t2 = new Task<int>(() => TaskMethod("Task 4", 2)); var complexTask = Task.WhenAll(t1, t2); var exceptionHandler = complexTask.ContinueWith(t =>
Console.WriteLine("Result: {0}", t.Result),
TaskContinuationOptions.OnlyOnFaulted
);
t1.Start();
t2.Start();
Task.WaitAll(t1, t2);
} catch (AggregateException ex)
{
ex.Handle(exception =>
{
Console.WriteLine(exception.Message); return true;
});
}
}
}
}
**async/await的方式:**
using System;using System.Threading;using System.Threading.Tasks;namespace ConsoleApp1
{ class Program
{ static async Task ThrowNotImplementedExceptionAsync()
{ throw new NotImplementedException();
} static async Task ThrowInvalidOperationExceptionAsync()
{ throw new InvalidOperationException();
} static async Task Normal()
{ await Fun();
} static Task Fun()
{ return Task.Run(() =>
{ for (int i = 1; i <= 10; i++)
{
Console.WriteLine("i={0}", i);
Thread.Sleep(200);
}
});
} static async Task ObserveOneExceptionAsync()
{ var task1 = ThrowNotImplementedExceptionAsync(); var task2 = ThrowInvalidOperationExceptionAsync(); var task3 = Normal(); try
{ //異步的方式
Task allTasks = Task.WhenAll(task1, task2, task3); await allTasks; //同步的方式 //Task.WaitAll(task1, task2, task3); } catch (NotImplementedException ex)
{
Console.WriteLine("task1 任務報錯!");
} catch (InvalidOperationException ex)
{
Console.WriteLine("task2 任務報錯!");
} catch (Exception ex)
{
Console.WriteLine("任務報錯!");
}
} public static void Main()
{
Task task = ObserveOneExceptionAsync();
Console.WriteLine("主線程繼續運作........");
task.Wait();
}
}
}
2.5、Task.FromResult的應用
using System;using System.Collections.Generic;using System.Threading;using System.Threading.Tasks;namespace ConsoleApp1
{ class Program
{ static IDictionary<string, string> cache = new Dictionary<string, string>()
{
{"0001","A"},
{"0002","B"},
{"0003","C"},
{"0004","D"},
{"0005","E"},
{"0006","F"},
}; public static void Main()
{
Task<string> task = GetValueFromCache("0006");
Console.WriteLine("主程式繼續執行。。。。"); string result = task.Result;
Console.WriteLine("result={0}", result);
} private static Task<string> GetValueFromCache(string key)
{
Console.WriteLine("GetValueFromCache開始執行。。。。"); string result = string.Empty; //Task.Delay(5000);
Thread.Sleep(5000);
Console.WriteLine("GetValueFromCache繼續執行。。。。"); if (cache.TryGetValue(key, out result))
{ return Task.FromResult(result);
} return Task.FromResult("");
}
}
}
2.6、使用IProgress實作異步程式設計的程序通知
IProgress隻提供了一個方法void Report(T value)，通過Report方法把一個T類型的值報告給IProgress,然後IProgress的實作類Progress的構造函數接收類型為Action的形參，通過這個委托讓進度顯示在UI界面中。
using System;
using System.Threading;
using System.Threading.Tasks;
namespace ConsoleApp1
{
class Program
{
static void DoProcessing(IProgress<int> progress)
{
for (int i = 0; i <= 100; ++i)
{
Thread.Sleep(100);
if (progress != null)
{
progress.Report(i);
}
}
}
static async Task Display()
{
//目前線程
var progress = new Progress<int>(percent =>
{
Console.Clear();
Console.Write("{0}%", percent);
});
//線程池線程
await Task.Run(() => DoProcessing(progress));
Console.WriteLine("");
Console.WriteLine("結束");
}
public static void Main()
{
Task task = Display();
task.Wait();
}
}
}
2.7、Factory.FromAsync的應用 (簡APM模式(委托)轉換為任務)(BeginXXX和EndXXX)
帶回調方式的
using System;
using System.Threading;
using System.Threading.Tasks;
namespace ConsoleApp1
{
class Program
{
private delegate string AsynchronousTask(string threadName);
private static string Test(string threadName)
{
Console.WriteLine("Starting...");
Console.WriteLine("Is thread pool thread: {0}", Thread.CurrentThread.IsThreadPoolThread);
Thread.Sleep(TimeSpan.FromSeconds(2));
Thread.CurrentThread.Name = threadName;
return string.Format("Thread name: {0}", Thread.CurrentThread.Name);
}
private static void Callback(IAsyncResult ar)
{
Console.WriteLine("Starting a callback...");
Console.WriteLine("State passed to a callbak: {0}", ar.AsyncState);
Console.WriteLine("Is thread pool thread: {0}", Thread.CurrentThread.IsThreadPoolThread);
Console.WriteLine("Thread pool worker thread id: {0}", Thread.CurrentThread.ManagedThreadId);
}
//執行的流程是 先執行Test--->Callback--->task.ContinueWith
static void Main(string[] args)
{
AsynchronousTask d = Test;
Console.WriteLine("Option 1");
Task<string> task = Task<string>.Factory.FromAsync(
d.BeginInvoke("AsyncTaskThread", Callback, "a delegate asynchronous call"), d.EndInvoke);
task.ContinueWith(t => Console.WriteLine("Callback is finished, now running a continuation! Result: {0}",
t.Result));
while (!task.IsCompleted)
{
Console.WriteLine(task.Status);
Thread.Sleep(TimeSpan.FromSeconds(0.5));
}
Console.WriteLine(task.Status);
}
}
}
不帶回調方式的
using System;
using System.Threading;
using System.Threading.Tasks;
namespace ConsoleApp1
{
class Program
{
private delegate string AsynchronousTask(string threadName);
private static string Test(string threadName)
{
Console.WriteLine("Starting...");
Console.WriteLine("Is thread pool thread: {0}", Thread.CurrentThread.IsThreadPoolThread);
Thread.Sleep(TimeSpan.FromSeconds(2));
Thread.CurrentThread.Name = threadName;
return string.Format("Thread name: {0}", Thread.CurrentThread.Name);
}
//執行的流程是 先執行Test--->task.ContinueWith
static void Main(string[] args)
{
AsynchronousTask d = Test;
Task<string> task = Task<string>.Factory.FromAsync(
d.BeginInvoke, d.EndInvoke, "AsyncTaskThread", "a delegate asynchronous call");
task.ContinueWith(t => Console.WriteLine("Task is completed, now running a continuation! Result: {0}",
t.Result));
while (!task.IsCompleted)
{
Console.WriteLine(task.Status);
Thread.Sleep(TimeSpan.FromSeconds(0.5));
}
Console.WriteLine(task.Status);
}
}
}