了解.NET 通用主机

写在前面

 .NET 通用主机负责应用启动和生存期管理，主机是封装应用资源和生存期功能的对象，通用主机可用于其他类型的 .NET 应用程序，如控制台应用；.NET 通用主机基于类库Microsoft.Extensions.Hosting 来实现，本文记录如何使用.NET 辅助角色服务模板来创建通用主机。

代码实现

以下示例是注册 IHostApplicationLifetime 事件的 IHostedService 实现

using Microsoft.Extensions.Hosting;
using Microsoft.Extensions.Logging;

public sealed class ExampleHostedService : IHostedService
{
    private readonly ILogger _logger;
    private IHostApplicationLifetime _applicationLifetime;

    public ExampleHostedService(
        ILogger<ExampleHostedService> logger,
        IHostApplicationLifetime appLifetime)
    {
        _logger = logger;

        appLifetime.ApplicationStarted.Register(OnStarted);
        appLifetime.ApplicationStopping.Register(OnStopping);
        appLifetime.ApplicationStopped.Register(OnStopped);

        _applicationLifetime = appLifetime;
    }

    public Task StartAsync(CancellationToken cancellationToken)
    {
        _logger.LogInformation("1. StartAsync has been called.");

        return Task.CompletedTask;
    }

    public Task StopAsync(CancellationToken cancellationToken)
    {
        _logger.LogInformation("4. StopAsync has been called.");

        return Task.CompletedTask;
    }

    private async void OnStarted()
    {
        _logger.LogInformation("2. OnStarted has been called.");

        var count = 0;
        var task = Task.Run(() =>
        {
            while (true)
            {
                count++;
                Console.WriteLine("running...");
                Thread.Sleep(1000);
                if (count == 5)
                {
                    _applicationLifetime.StopApplication();
                }
            }
        });
    }

    private void OnStopping()
    {
        _logger.LogInformation("3. OnStopping has been called.");
    }

    private void OnStopped()
    {
        _logger.LogInformation("5. OnStopped has been called.");
    }
}

修改辅助角色服务模板以添加 ExampleHostedService 实现

using Microsoft.Extensions.Hosting;
using Microsoft.Extensions.DependencyInjection;

HostApplicationBuilder builder = Host.CreateApplicationBuilder(args);
builder.Services.AddHostedService<ExampleHostedService>();

IHost host = builder.Build();
host.Run();
 
Environment.Exit(0);

调用示例

运行示例后可以用Ctrl+C或等待5秒后退出主机应用的执行流程，调用结果如下：