【C# .NET】chapter 13 使用多任务改进性能和可扩展性
目录
一、物理内存和虚拟内存使用（Recorder 类）
二、 对比 string的“+”操作与stringbuilder 操作 的处理效率，内存消耗情况，
三、异步运行任务、三种启动任务方法、将上一任务方法处理结果作为参数传给下一任务方法
四、嵌套子任务
五、同步访问共享资源 Monitor.TryEnter、Monitor.Exit、 原子操作 Interlocked.Increment
六、理解async 和 await :改进控制台响应。 Main方法async Task
七、支持多任务的普通类型
八、异步流 返回类型IEnumerable
一、物理内存和虚拟内存使用（Recorder 类）
using System;
using System.Diagnostics;
using static System.Console;
using static System.Diagnostics.Process;namespace Packt.Shared
{public static class Recorder{static Stopwatch timer = new Stopwatch();static long bytesPhysicalBefore = 0;static long bytesVirtualBefore = 0;public static void Start(){// force two garbage collections to release memory that is no// longer referenced but has not been released yet// // 强制两次垃圾回收释放不再被引用但尚未释放的内存GC.Collect();GC.WaitForPendingFinalizers();//挂起当前线程，直到正在处理终结器队列的线程清空该队列。GC.Collect();//强制立即对所有代进行垃圾回收。//存储当前物理和虚拟内存使用 store the current physical and virtual memory usebytesPhysicalBefore = GetCurrentProcess().WorkingSet64;bytesVirtualBefore = GetCurrentProcess().VirtualMemorySize64;timer.Restart();}public static void Stop(){timer.Stop();long bytesPhysicalAfter = GetCurrentProcess().WorkingSet64;//计时停止时的 物理内存和虚拟内存使用long bytesVirtualAfter = GetCurrentProcess().VirtualMemorySize64;WriteLine("{0:N0} physical bytes used.",bytesPhysicalAfter - bytesPhysicalBefore);WriteLine("{0:N0} virtual bytes used.",bytesVirtualAfter - bytesVirtualBefore);WriteLine("{0} time span ellapsed.", timer.Elapsed);WriteLine("{0:N0} total milliseconds ellapsed.",timer.ElapsedMilliseconds);//获取当前实例测量的总运行时间，以毫秒为单位。}}
}二、 对比 string的“+”操作与stringbuilder 操作 的处理效率，内存消耗情况，
using System;
using System.Linq;
using Packt.Shared;
using static System.Console;namespace MonitoringApp
{class Program{static void Main(string[] args){/*WriteLine("Processing. Please wait...");Recorder.Start();// simulate a process that requires some memory resources...int[] largeArrayOfInts = Enumerable.Range(1, 10_000).ToArray();// ...and takes some time to completeSystem.Threading.Thread.Sleep(new Random().Next(5, 10) * 1000);Recorder.Stop();*/int[] numbers = Enumerable.Range(1, 50_000).ToArray();//生成指定范围内的整数序列。WriteLine("Using string with +");Recorder.Start();string s = "";for (int i = 0; i < numbers.Length; i++){s += numbers[i] + ", ";}Recorder.Stop();/*Using string with +35,196,928 physical bytes used.6,291,456 virtual bytes used.00:00:04.0648349 time span ellapsed.4,064 total milliseconds ellapsed.Using StringBuilder0 physical bytes used.0 virtual bytes used.00:00:00.0018665 time span ellapsed.1 total milliseconds ellapsed.*/WriteLine("Using StringBuilder");Recorder.Start();var builder = new System.Text.StringBuilder();for (int i = 0; i < numbers.Length; i++){builder.Append(numbers[i]); builder.Append(", ");}Recorder.Stop();ReadLine();}}
}三、异步运行任务、三种启动任务方法、将上一任务方法处理结果作为参数传给下一任务方法
using System;
using System.Threading;
using System.Threading.Tasks;
using System.Diagnostics;
using static System.Console;namespace WorkingWithTasks
{class Program{static void MethodA(){WriteLine("Starting Method A...");Thread.Sleep(3000); // simulate three seconds of work WriteLine("Finished Method A.");}static void MethodB(){WriteLine("Starting Method B...");Thread.Sleep(2000); // simulate two seconds of work WriteLine("Finished Method B.");}static void MethodC(){WriteLine("Starting Method C...");Thread.Sleep(1000); // simulate one second of work WriteLine("Finished Method C.");}static decimal CallWebService(){WriteLine("Starting call to web service...");Thread.Sleep((new Random()).Next(2000, 4000));WriteLine("Finished call to web service.");return 89.99M;}static string CallStoredProcedure(decimal amount){WriteLine("Starting call to stored procedure...");Thread.Sleep((new Random()).Next(2000, 4000));WriteLine("Finished call to stored procedure.");return $"12 products cost more than {amount:C}.";}static void Main(string[] args){var timer = Stopwatch.StartNew();// WriteLine("Running methods synchronously on one thread.");// MethodA();// MethodB();// MethodC();/* //开启任务的三种方法WriteLine("Running methods asynchronously on multiple threads.");Task taskA = new Task(MethodA);taskA.Start();Task taskB = Task.Factory.StartNew(MethodB);Task taskC = Task.Run(new Action(MethodC));Task[] tasks = { taskA, taskB, taskC };Task.WaitAll(tasks);*/WriteLine("Passing the result of one task as an input into another.");//将CallWebService的结果作为输入传给CallStoredProcedure任务var taskCallWebServiceAndThenStoredProcedure =Task.Factory.StartNew(CallWebService).ContinueWith(previousTask =>CallStoredProcedure(previousTask.Result));WriteLine($"Result: {taskCallWebServiceAndThenStoredProcedure.Result}");WriteLine($"{timer.ElapsedMilliseconds:#,##0}ms elapsed.");ReadLine();}}
}四、嵌套子任务
using System;
using System.Threading;
using System.Threading.Tasks;
using System.Diagnostics;
using static System.Console;namespace NestedAndChildTasks
{class Program{static void OuterMethod(){WriteLine("Outer method starting...");var inner = Task.Factory.StartNew(InnerMethod,TaskCreationOptions.AttachedToParent);//开启嵌套任务WriteLine("Outer method finished.");}static void InnerMethod()//嵌套子任务方法{WriteLine("Inner method starting...");Thread.Sleep(2000);WriteLine("Inner method finished.");}static void Main(string[] args){var outer = Task.Factory.StartNew(OuterMethod);outer.Wait();//等待嵌套子任务完成后才继续WriteLine("Console app is stopping.");}}
}五、同步访问共享资源 Monitor.TryEnter、Monitor.Exit、 原子操作 Interlocked.Increment
using System;
using System.Threading;
using System.Threading.Tasks;
using System.Diagnostics;
using static System.Console;namespace SynchronizingResourceAccess
{class Program{static Random r = new Random();static string Message; // 一个共享资源static int Counter; //另一共享资源static object conch = new object();//互斥锁static void MethodA(){try{ //在指定的时间内尝试获取指定对象的独占锁。if (Monitor.TryEnter(conch, TimeSpan.FromSeconds(15))){for (int i = 0; i < 5; i++){Thread.Sleep(r.Next(2000));Message += "A";Interlocked.Increment(ref Counter);//递增指定变量并将结果存储为原子操作。Write(".");}}else{WriteLine("Method A failed to enter a monitor lock.");}}finally{Monitor.Exit(conch);//释放指定对象上的独占锁。}}static void MethodB(){try{if (Monitor.TryEnter(conch, TimeSpan.FromSeconds(15))){for (int i = 0; i < 5; i++){Thread.Sleep(r.Next(2000));Message += "B";Interlocked.Increment(ref Counter);Write(".");}}else{WriteLine("Method B failed to enter a monitor lock.");}}finally{Monitor.Exit(conch);}}/*Please wait for the tasks to complete...........Results: AAAAABBBBB.9,083 elapsed milliseconds.10 string modifications.*/static void Main(string[] args){WriteLine("Please wait for the tasks to complete.");Stopwatch watch = Stopwatch.StartNew();Task a = Task.Factory.StartNew(MethodA);Task b = Task.Factory.StartNew(MethodB);Task.WaitAll(new Task[] { a, b });WriteLine();WriteLine($"Results: {Message}.");WriteLine($"{watch.ElapsedMilliseconds:#,##0} elapsed milliseconds.");WriteLine($"{Counter} string modifications.");ReadLine();}}
}
六、理解async 和 await :改进控制台响应。 Main方法async Task
从C#6开始可以在try\\catch块中使用await
using System;
using System.Net.Http;
using System.Threading.Tasks;
using static System.Console;namespace AsyncConsole
{class Program{static async Task Main(string[] args){var client = new HttpClient();HttpResponseMessage response =await client.GetAsync("http://www.apple.com/");WriteLine("Apple's home page has {0:N0} bytes.",response.Content.Headers.ContentLength);}}
}七、支持多任务的普通类型
八、异步流 返回类型IEnumerable
using System;
using System.Collections.Generic;
using System.Threading.Tasks;
using static System.Console;namespace AsyncEnumerable
{class Program{async static IAsyncEnumerable<int> GetNumbers(){var r = new Random();// simulate workawait Task.Run(() => Task.Delay(r.Next(1500, 3000)));yield return r.Next(0, 1001);await Task.Run(() => Task.Delay(r.Next(1500, 3000)));yield return r.Next(0, 1001);await Task.Run(() => Task.Delay(r.Next(1500, 3000)));yield return r.Next(0, 1001);}static async Task Main(string[] args){await foreach (int number in GetNumbers()){WriteLine($"Number: {number}");}}}
}