标签：task fse pac can ext ken eth ring contain
C# 5.0 引入了async/await，.net framework4.5开始支持该用法
使用：
由async标识的方法必须带有await，如果不带await，方法将被同步执行
static void Main(string[] args)
{
fun22();
Console.WriteLine($"Main await ThreadId {Thread.CurrentThread.ManagedThreadId}");
Console.ReadKey();
}
private async static void fun22()
{
//sync同步(相对于调用函数的线程)
Console.WriteLine($"pre await ThreadId {Thread.CurrentThread.ManagedThreadId}");
await HelloWorld();
//async异步(相对于调用函数的线程)
Console.WriteLine($"after await ThreadId {Thread.CurrentThread.ManagedThreadId}");
}
private static Task HelloWorld()
{
//sync同步(相对于调用函数的线程)
Console.WriteLine($"pre Task ThreadId {Thread.CurrentThread.ManagedThreadId}");
//async异步(相对于调用函数的线程)
return Task.Factory.StartNew(() =>
{
Thread.Sleep(1000);
Console.WriteLine($"Task ThreadId {Thread.CurrentThread.ManagedThreadId}");
});
}
运行结果：
结果说明：
只有执行到Task异步的时候，才使真正的异步
微软的例子：
using System;
using System.IO;
namespace ConsoleApplication
{
class Program
{
static async Task Main()
{
await ReadCharacters();
}
static async Task ReadCharacters()
{
String result;
using (StreamReader reader = File.OpenText("existingfile.txt"))
{
Console.WriteLine("Opened file.");
result = await reader.ReadToEndAsync();
Console.WriteLine("Contains: " + result);
}
}
}
}
查看ReadToEndAsync源码，发现最后是TaskFactory<Int32>.FromAsyncTrim，真正的异步由这个函数执行，也就是真正的异步是由Task的线程池执行的。
[HostProtection(ExternalThreading = true)]
[ComVisible(false)]
public Task<int> ReadAsync(Byte[] buffer, int offset, int count)
{
return ReadAsync(buffer, offset, count, CancellationToken.None);
}
[HostProtection(ExternalThreading = true)]
[ComVisible(false)]
public virtual Task<int> ReadAsync(Byte[] buffer, int offset, int count, CancellationToken cancellationToken)
{
// If cancellation was requested, bail early with an already completed task.
// Otherwise, return a task that represents the Begin/End methods.
return cancellationToken.IsCancellationRequested
? Task.FromCancellation<int>(cancellationToken)
: BeginEndReadAsync(buffer, offset, count);
}
private Task<Int32> BeginEndReadAsync(Byte[] buffer, Int32 offset, Int32 count)
{
return TaskFactory<Int32>.FromAsyncTrim(
this, new ReadWriteParameters { Buffer = buffer, Offset = offset, Count = count },
(stream, args, callback, state) => stream.BeginRead(args.Buffer, args.Offset, args.Count, callback, state), // cached by compiler
(stream, asyncResult) => stream.EndRead(asyncResult)); // cached by compiler
}
标签：task fse pac can ext ken eth ring contain
原文地址：https://www.cnblogs.com/yaosj/p/10623081.html
