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寫在前面
停了近一個(gè)月的技術(shù)博客，隨著正式脫離996的魔窟，接下來也正式恢復(fù)了。本文從源碼角度進(jìn)一步討論.NET Core 3.0
中關(guān)于Host擴(kuò)展的一些技術(shù)點(diǎn)，主要討論Long Run Program的創(chuàng)建與守護(hù)。
關(guān)于Host，我們最容易想到的就是程序的啟動(dòng)與停止，而其中隱藏著非常關(guān)鍵的功能，就是Host的初始化，我們所需要的所有資源都必須而且應(yīng)該在程序啟動(dòng)過程中初始化完成，當(dāng)然本文的主要內(nèi)容并不是Host初始化，前文已經(jīng)累述。當(dāng)然，為了更好的守護(hù)與管理已經(jīng)啟動(dòng)的Host，.NET
Core 3.0將程序的生命周期事件的訂閱開放給開發(fā)者，當(dāng)然也包括自定義的Host Service對(duì)象。
注：本文代碼基于.NET Core 3.0 Preview9
<https://img2018.cnblogs.com/blog/533598/201909/533598-20190914220234020-1611831647.png>
.NET Core 3.0中創(chuàng)建Long Run Program
IHost與IHostBuilder
當(dāng)我們創(chuàng)建Long Run Program時(shí)，會(huì)首先關(guān)注程序的啟動(dòng)與停止，.NET Core
3.0為此提供了一個(gè)接口IHost，該接口位于Microsoft.Extensions.Hosting類庫中，其源碼如下：
1: /// <summary> 2: /// A program abstraction. 3: /// </summary> 4: public
interface IHost : IDisposable 5: { 6: /// <summary> 7: /// The programs
configured services. 8: /// </summary> 9: IServiceProvider Services { get; }
10:? 11: /// <summary> 12: /// Start the program. 13: /// </summary> 14:
/// <param name="cancellationToken">Used to abort program start.</param> 15:
/// <returns>A <see cref="Task"/> that will be completed when the <see
cref="IHost"/> starts.</returns> 16: Task StartAsync(CancellationToken
cancellationToken =default); 17: ? 18: /// <summary> 19: /// Attempts to
gracefully stop the program. 20: /// </summary> 21: /// <param
name="cancellationToken">Used to indicate when stop should no longer be
graceful.</param> 22: /// <returns>A <see cref="Task"/> that will be completed
when the <see cref="IHost"/> stops.</returns> 23: Task
StopAsync(CancellationToken cancellationToken =default); 24: }
該接口含有一個(gè)只讀屬性：IServiceProvider Services { get; }，通過該屬性，我們可以拿到所有Host初始化時(shí)所注入的對(duì)象信息。
IHostBuilder接口所承擔(dān)的核心功能就是程序的初始化，通過：IHost
Build()來完成，當(dāng)然只需要運(yùn)行一次即可。其初始化內(nèi)容一般包括以下幾個(gè)功能：
<https://img2018.cnblogs.com/blog/533598/201909/533598-20190914220234654-1227722267.png>
另外需要說明的是，以上功能的初始化，是通過IHostBuilder提供的接口獲取用戶輸入的信息后，通過調(diào)用Build()方法來完成初始化。以下為IHostBuilder的部分源代碼：
1: /// <summary> 2: /// Set up the configuration for the builder itself.
This will be used to initialize the <see cref="IHostEnvironment"/> 3: /// for
use later in the build process. This can be called multiple times and the
results will be additive. 4: /// </summary> 5: /// <param
name="configureDelegate">The delegate for configuring the <see
cref="IConfigurationBuilder"/> that will be used 6: /// to construct the <see
cref="IConfiguration"/> for the host.</param> 7: /// <returns>The same
instance of the <see cref="IHostBuilder"/> for chaining.</returns> 8: public
IHostBuilder ConfigureHostConfiguration(Action<IConfigurationBuilder>
configureDelegate) 9: { 10:
_configureHostConfigActions.Add(configureDelegate ??throw new
ArgumentNullException(nameof(configureDelegate))); 11: return this; 12: } 13:
? 14: /// <summary> 15: /// Adds services to the container. This can be
called multiple times and the results will be additive. 16: /// </summary> 17:
/// <param name="configureDelegate">The delegate for configuring the <see
cref="IConfigurationBuilder"/> that will be used 18: /// to construct the <see
cref="IConfiguration"/> for the host.</param> 19: /// <returns>The same
instance of the <see cref="IHostBuilder"/> for chaining.</returns> 20: public
IHostBuilder ConfigureServices(Action<HostBuilderContext, IServiceCollection>
configureDelegate) 21: { 22: _configureServicesActions.Add(configureDelegate
??throw new ArgumentNullException(nameof(configureDelegate))); 23: return this;
24:} 25: ? 26: /// <summary> 27: /// Overrides the factory used to create
the service provider. 28: /// </summary> 29: /// <typeparam
name="TContainerBuilder">The type of the builder to create.</typeparam> 30:
/// <param name="factory">A factory used for creating service providers.</param>
31:/// <returns>The same instance of the <see cref="IHostBuilder"/> for
chaining.</returns> 32: public IHostBuilder
UseServiceProviderFactory<TContainerBuilder>(IServiceProviderFactory<TContainerBuilder>
factory) 33: { 34: _serviceProviderFactory = new
ServiceFactoryAdapter<TContainerBuilder>(factory ??throw new
ArgumentNullException(nameof(factory))); 35: return this; 36: } 37: ? 38:
/// <summary> 39: /// Enables configuring the instantiated dependency
container. This can be called multiple times and 40: /// the results will be
additive. 41: /// </summary> 42: /// <typeparam name="TContainerBuilder">The
type of the builder to create.</typeparam> 43: /// <param
name="configureDelegate">The delegate for configuring the <see
cref="IConfigurationBuilder"/> that will be used 44: /// to construct the <see
cref="IConfiguration"/> for the host.</param> 45: /// <returns>The same
instance of the <see cref="IHostBuilder"/> for chaining.</returns> 46: public
IHostBuilder ConfigureContainer<TContainerBuilder>(Action<HostBuilderContext,
TContainerBuilder> configureDelegate) 47: { 48:
_configureContainerActions.Add(new
ConfigureContainerAdapter<TContainerBuilder>(configureDelegate 49: ?? throw
new ArgumentNullException(nameof(configureDelegate)))); 50: return this; 51: }
IHostService
文章開頭有說過自定義Host
Service對(duì)象，那么我們?nèi)绾巫远x呢，其實(shí)很簡(jiǎn)單只需要實(shí)現(xiàn)IHostService，并在ConfigureServices中調(diào)用services.AddHostedService<MyServiceA>()即可，以下是IHostService的源碼：
1: /// <summary> 2: /// Defines methods for objects that are managed by the
host. 3: /// </summary> 4: public interface IHostedService 5: { 6: ///
<summary> 7: /// Triggered when the application host is ready to start the
service. 8: /// </summary> 9: /// <param name="cancellationToken">Indicates
that the start process has been aborted.</param> 10: Task
StartAsync(CancellationToken cancellationToken); 11: ? 12: /// <summary> 13:
/// Triggered when the application host is performing a graceful shutdown. 14:
/// </summary> 15: /// <param name="cancellationToken">Indicates that the
shutdown process should no longer be graceful.</param> 16: Task
StopAsync(CancellationToken cancellationToken); 17: }
根據(jù)源碼我們可以知道，該接口只有兩個(gè)方法，即代碼程序開始與停止的方法。具體的實(shí)現(xiàn)可以參考如下：
1: public class MyServiceA : IHostedService, IDisposable 2: { 3: private
bool _stopping; 4: private Task _backgroundTask; 5: ? 6: public
MyServiceA(ILoggerFactory loggerFactory) 7: { 8: Logger =
loggerFactory.CreateLogger<MyServiceB>(); 9: } 10: ? 11: public ILogger
Logger { get; } 12: ? 13: public Task StartAsync(CancellationToken
cancellationToken) 14: { 15: Logger.LogInformation("MyServiceB is starting."
); 16: _backgroundTask = BackgroundTask(); 17: return Task.CompletedTask;
18: } 19: ? 20: private async Task BackgroundTask() 21: { 22: while
(!_stopping) 23: { 24: await Task.Delay(TimeSpan.FromSeconds(7)); 25:
Logger.LogInformation("MyServiceB is doing background work."); 26: } 27: ?
28: Logger.LogInformation("MyServiceB background task is stopping."); 29: }
30:? 31: public async Task StopAsync(CancellationToken cancellationToken) 32:
{ 33: Logger.LogInformation("MyServiceB is stopping."); 34: _stopping =
true; 35: if (_backgroundTask != null) 36: { 37: // TODO: cancellation 38:
await _backgroundTask; 39: } 40: } 41: ? 42: public void Dispose() 43:
{ 44: Logger.LogInformation("MyServiceB is disposing."); 45: } 46: }
IHostService是我們自定義Host管理對(duì)象的入口，所有需要壓入到Host托管的對(duì)象都必須要實(shí)現(xiàn)此接口。
Host生命周期的管理
該接口提供了一種我們可以在程序運(yùn)行期間進(jìn)行管理的功能，如程序的啟動(dòng)與停止事件的訂閱，關(guān)于Host生命周期的管理，主要由IHostApplicationLifetime和IHostLifetime這兩個(gè)接口來完成。
以下是IHostApplicationLifetime的源碼?
1: public interface IHostApplicationLifetime 2: { 3: /// <summary> 4: ///
Triggered when the application host has fully started. 5: /// </summary> 6:
CancellationToken ApplicationStarted { get; } 7: ? 8: /// <summary> 9: ///
Triggered when the application host is performing a graceful shutdown. 10: ///
Shutdown will block until this event completes. 11: /// </summary> 12:
CancellationToken ApplicationStopping { get; } 13: ? 14: /// <summary> 15:
/// Triggered when the application host is performing a graceful shutdown. 16:
/// Shutdown will block until this event completes. 17: /// </summary> 18:
CancellationToken ApplicationStopped { get; } 19: ? 20: /// <summary> 21:
/// Requests termination of the current application. 22: /// </summary> 23:
void StopApplication(); 24: }
IHostLifetime源碼如下：
1: public interface IHostLifetime 2: { 3: /// <summary> 4: /// Called at
the start of <see cref="IHost.StartAsync(CancellationToken)"/> which will wait
until it's complete before 5: /// continuing. This can be used to delay
startup until signaled by an external event. 6: /// </summary> 7: /// <param
name="cancellationToken">Used to indicate when stop should no longer be
graceful.</param> 8: /// <returns>A <see cref="Task"/>.</returns> 9: Task
WaitForStartAsync(CancellationToken cancellationToken); 10: ? 11: ///
<summary> 12: /// Called from <see cref="IHost.StopAsync(CancellationToken)"/>
to indicate that the host is stopping and it's time to shut down. 13: ///
</summary> 14: /// <param name="cancellationToken">Used to indicate when stop
should no longer be graceful.</param> 15: /// <returns>A <see
cref="Task"/>.</returns> 16: Task StopAsync(CancellationToken
cancellationToken); 17: }
具體的使用可以參考如下代碼：
1: public class MyLifetime : IHostLifetime, IDisposable 2: { 3: .........
4:? 5: private IHostApplicationLifetime ApplicationLifetime { get; } 6: ? 7:
public ConsoleLifetime(IHostApplicationLifetime applicationLifetime) 8: { 9:
ApplicationLifetime = applicationLifetime ??throw new
ArgumentNullException(nameof(applicationLifetime)); 10: } 11: ? 12: public
Task WaitForStartAsync(CancellationToken cancellationToken) 13: { 14:
_applicationStartedRegistration =
ApplicationLifetime.ApplicationStarted.Register(state => 15: { 16:
((ConsoleLifetime)state).OnApplicationStarted(); 17: }, 18: this); 19:
_applicationStoppingRegistration =
ApplicationLifetime.ApplicationStopping.Register(state => 20: { 21:
((ConsoleLifetime)state).OnApplicationStopping(); 22: }, 23: this); 24: ?
25: ....... 26: ? 27: return Task.CompletedTask; 28: } 29: ? 30: private
void OnApplicationStarted() 31: { 32: Logger.LogInformation("Application
started. Press Ctrl+C to shut down."); 33: Logger.LogInformation("Hosting
environment: {envName}", Environment.EnvironmentName); 34:
Logger.LogInformation("Content root path: {contentRoot}",
Environment.ContentRootPath); 35: } 36: ? 37: private void
OnApplicationStopping() 38: { 39: Logger.LogInformation("Application is
shutting down..."); 40: } 41: ? 42: ........ 43: }
總結(jié)
至此，我們知道了創(chuàng)建Long Run
Program所需要關(guān)注的幾個(gè)點(diǎn)，分別是繼承IHostService、訂閱程序的生命周期時(shí)間以及Host的初始化過程。相對(duì)來說這段內(nèi)容還是比較簡(jiǎn)單的，但是開發(fā)過程中，依然會(huì)遇到很多的問題，比如任務(wù)的定時(shí)機(jī)制、消息的接入、以及程序的性能優(yōu)化等等，這些都需要我們?cè)趯?shí)踐中進(jìn)一步總結(jié)完善。
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