.NET Core多线程通关 (2) 异步
大家好
去年换工作时系统复习了一下.NET Core多线程相关专题，学习了一线码农老哥的《.NET 5多线程编程实战》课程，我将复习的知识进行了总结形成本专题。
理解异步的本质
时间片切换成本高！
CPU密集型操作：编码解码、图形计算、正则表达式等
IO密集型操作：和硬件打交道，和DB打交道等
线程太多的烦恼/代价：
新开Thread是有开销的（时间、空间）
GC回收会冻结所有线程寻找引用根（gcroot）
Thread会和网络驱动程序打交道（外网络地址）
ThreadPool中的WorkQueue任务（4000+）得不到处理
异步：async/await
程序有可能会卡死！
（3）C#如何使用异步？
workThread：
适用于CPU密集型，在WinDbg中标签为 ThreadPool Worker
IOThread：
适用于IO密集型，在WinDbg中标签为 ThreadPool Completion Port
namespace ConsoleApp3{class Program{static void Main(string[] args){GetContentLengthAsync("http://cnblogs.com");Console.WriteLine($"主线程:{Environment.CurrentManagedThreadId}, 准备退出！");Console.ReadLine();}static async Task<int> GetContentLengthAsync(string url){using (HttpClient client = new HttpClient()){var content = await client.GetStringAsync(url);Console.WriteLine($"当前线程:{Environment.CurrentManagedThreadId}, content={content.Length}");return content.Length;}}}}
初始化时将SafeHandle、ThreadPool与IO完成端口进行绑定（比如：FileStream在Init时）
（主线程）创建IO完成端口：CreateIoCompletionPort(IntPtr FileHandle, IntPtr ExistingCompletionPort, IntPtr CompletionKey, uint NumberOfConcurrentThreads)
（主线程）将消息塞到IO完成端口的Queue队列：PostQueuedCompletionStatus
（子线程）从IO完成端口的Queue队列中获取消息：GetQueuedCompletionStatus
public class IOCP{[DllImport("kernel32.dll", CharSet = CharSet.Auto, SetLastError = true)]public static extern SafeFileHandle CreateIoCompletionPort(IntPtr FileHandle, IntPtr ExistingCompletionPort, IntPtr CompletionKey, uint NumberOfConcurrentThreads);[DllImport("kernel32.dll", CharSet = CharSet.Auto, SetLastError = true)]public static extern bool GetQueuedCompletionStatus(SafeFileHandle CompletionPort,out uint lpNumberOfBytesTransferred, out IntPtr lpCompletionKey,out IntPtr lpOverlapped, uint dwMilliseconds);[DllImport("Kernel32", CharSet = CharSet.Auto)]public static extern bool PostQueuedCompletionStatus(SafeFileHandle CompletionPort, uint dwNumberOfBytesTransferred, IntPtr dwCompletionKey, IntPtr lpOverlapped);}
// 1. 创建IO完成端口var safehandle = IOCP.CreateIoCompletionPort(new IntPtr(-1), IntPtr.Zero, IntPtr.Zero, 1);var thread = new Thread(() =>{Console.WriteLine($"工作线程: {Environment.CurrentManagedThreadId} 开始获取数据...");while (true){// 3. get数据IOCP.GetQueuedCompletionStatus(safehandle, out var ipn, out var ipc, out var lop, int.MaxValue);var receiveData = Convert.ToString(GCHandle.FromIntPtr(lop).Target);Console.WriteLine($"工作线程: {Environment.CurrentManagedThreadId} 获取数据成功！{receiveData}");Thread.Sleep(1000);}});thread.Start();// 2. post 数据var data = (IntPtr)GCHandle.Alloc("hello world");IOCP.PostQueuedCompletionStatus(safehandle, 4096, IntPtr.Zero, data);Console.WriteLine($"主线程: {Environment.CurrentManagedThreadId} 塞入数据成功！");Console.ReadLine();
/// <summary>/// continutewith 的版本/// </summary>/// <returns></returns>static Task<List<string>> GetContentListContinute(){var list = new List<string>();SqlConnection connection = new SqlConnection("Server=LocalHost; Persist Security Info=False;Integrated Security=SSPI;Database= PostDB;");var task = connection.OpenAsync().ContinueWith(t =>{SqlCommand command = new SqlCommand("select PostContent from Post", connection);return command.ExecuteReaderAsync().ContinueWith(t2 =>{var reader = t2.Result;return GetContent(reader, list).ContinueWith(t3 =>{return list;});}).Unwrap();}).Unwrap();return task;}static Task<bool> GetContent(SqlDataReader reader, List<string> list){return reader.ReadAsync().ContinueWith(t =>{var hasRow = t.Result;if (hasRow){list.Add(reader.GetString(0)); //读取reader的值GetContent(reader, list);}return false;});}/// <summary>/// await+async 的异步写法/// </summary>/// <returns></returns>static async Task<List<string>> GetContentListAsync(){List<string> list = new List<string>();SqlConnection connection = new SqlConnection("Server=LocalHost; Persist Security Info=False;Integrated Security=SSPI;Database= PostDB;");await connection.OpenAsync();SqlCommand command = new SqlCommand("select PostContent from Post", connection);var reader = command.ExecuteReader();while (await reader.ReadAsync()){list.Add(reader.GetString(0));}return list;}
public interface IAsyncStateMachine{ void MoveNext(); void SetStateMachine(IAsyncStateMachine stateMachine);}step1.初始化一个异步状态机machine
step2.初始化一个AsyncTaskMethodBuilder的实例，赋予machine.builder
step3.设置异步状态机的状态为-1，将类传入到状态机内部
step4.调用machine.builder的start方法
step5.返回machine.builder.Task
（3）.NET提供异步方式的总结：
.NET 4.5开始提供的async/await，本质是.NET 4.0的Task + 状态机
.NET 4.0开始提供的Task，本质是.NET 3.5提供的Thread+ThreadPool+等待/取消等API操作
.NET Core多线程通关 (2) 异步
大家好去年换工作时系统复习了一下.NET Core多线程相关专题，学习了一线码农老哥的《.NET 5多线程编程实战》课程，我将复习的知识进行了...
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本文2024-09-16 17:45:37发表“云星空知识”栏目。
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