定时任务组件，除了 Hangfire 外，还有一个 Quarz.NET，不过 Hangfire .NET Core 支持的会更好些。

ASP.NET Core 使用 Hangfire 很简单，首先，Nuget 安装程序包：

> install-package Hangfire -pre

然后ConfigureServices添加配置代码：

public void ConfigureServices(IServiceCollection services)
{
    services.AddHangfire(x => x.UseSqlServerStorage("<name or connection string>"));
}

上面配置的是 Hangfire 任务配置数据库信息，默认只支持 SQLServer，如果不想使用数据库的话，可以 Nuget 安装程序包：

> install-package Hangfire.MemoryStorage -pre

修改ConfigureServices配置代码：

public void ConfigureServices(IServiceCollection services)
{
    services.AddHangfire(x => x..UseStorage(new MemoryStorage()));
}

Hangfire 扩展（比如 MySql）：https://www.hangfire.io/extensions.html

然后Configure添加配置代码：

public void Configure(IApplicationBuilder app, IHostingEnvironment env, ILoggerFactory loggerFactory)
{
    app.UseHangfireServer();
    app.UseHangfireDashboard();

    RecurringJob.AddOrUpdate(() => Console.WriteLine("Recurring!"), Cron.Minutely());
}

上面配置代码一分钟执行一次，Hangfire 支持 UI 界面展示，地址：http://localhost:8089/hangfire

Hangfire 默认也支持执行异步方法，RecurringJob方法签名：

public static void AddOrUpdate<T>(Expression<Func<T, Task>> methodCall, string cronExpression, TimeZoneInfo timeZone = null, string queue = "default");
public static void AddOrUpdate(Expression<Func<Task>> methodCall, string cronExpression, TimeZoneInfo timeZone = null, string queue = "default");
public static void AddOrUpdate<T>(Expression<Func<T, Task>> methodCall, Func<string> cronExpression, TimeZoneInfo timeZone = null, string queue = "default");
public static void AddOrUpdate(Expression<Func<Task>> methodCall, Func<string> cronExpression, TimeZoneInfo timeZone = null, string queue = "default");

异步和同步使用没有任何区别，示例代码：

public void Configure(IApplicationBuilder app, IHostingEnvironment env, ILoggerFactory loggerFactory)
{
    app.UseHangfireServer();
    app.UseHangfireDashboard();

    RecurringJob.AddOrUpdate(() => TestAsync(), Cron.Minutely());
}

public static async Task TestAsync()
{
    // to do...
}