我正在开发一个基于ASP.NET Core 3.1的项目，想要为它添加一个特定的功能，即在由文章作者指定的日期和时间安排一篇文章的发布（类似于WordPress通过其cron jobs安排计划发布的文章）。例如，如果我们从用户那里收到以下日期和时间：
2020-09-07 14:08:07
那么，我该如何使用托管服务调度后台任务仅运行一次并更改数据库中的标志并保存更改？
我已经阅读了一些相关文章，但它们没有指定日期和时间，只是提到了每5秒执行重复任务等与cron表达式有关的内容，但是我需要知道的是如何按照特定日期和时间安排后台任务？
提前感谢您。
我将CrontabSchedule与IHostedService相结合。下面的实现是轻量级的（没有强制架构的库）并且没有轮询。
public class SomeScheduledService: IHostedService
{
private readonly CrontabSchedule _crontabSchedule;
private DateTime _nextRun;
private const string Schedule = "0 0 1 * * *"; // run day at 1 am
private readonly SomeTask _task;
public SomeScheduledService(SomeTask task)
{
_task = Task;
_crontabSchedule = CrontabSchedule.Parse(Schedule, new CrontabSchedule.ParseOptions{IncludingSeconds = true});
_nextRun = _crontabSchedule.GetNextOccurrence(DateTime.Now);
}
public Task StartAsync(CancellationToken cancellationToken)
{
Task.Run(async () =>
{
while (!cancellationToken.IsCancellationRequested)
{
await Task.Delay(UntilNextExecution(), cancellationToken); // wait until next time
await _task.Execute(); //execute some task
_nextRun = _crontabSchedule.GetNextOccurrence(DateTime.Now);
}
}, cancellationToken);
return Task.CompletedTask;
}
private int UntilNextExecution() => Math.Max(0, (int)_nextRun.Subtract(DateTime.Now).TotalMilliseconds);
public Task StopAsync(CancellationToken cancellationToken) => Task.CompletedTask;
}
NCrontab.Signed包？这是你的代码使用的库吗？ - T3.0_nextRun = _crontabSchedule.GetNextOccurrence(_nextRun > DateTime.Now ? _nextRun : DateTime.Now); - undefinedSystem.Threading.Timer 和 Timespan 进行了操作，例如：public class ScheduleTask : IScheduler, IDisposable
{
private Timer _timer;
private IBackgroundTaskQueue TaskQueue { get; }
// Set task to schedule for a specific date and time
public async Task SetAndQueueTaskAsync(ScheduleTypeEnum scheduleType, DateTime scheduleFor, Guid scheduledItemId)
{
// Omitted for simplicity
// ....
TaskQueue.QueueBackgroundWorkItem(SetTimer);
}
// ......
// lines omitted for simplicity
// .....
// Set timer for schedule item
private Task SetTimer(CancellationToken stoppingToken)
{
// ......
// lines omitted for simplicity
// .....
_timer = new Timer(DoWork, null, (item.ScheduledFor - DateTime.UtcNow).Duration(), TimeSpan.Zero);
return Task.CompletedTask;
}
private void DoWork(object state)
{
ScheduledItemChangeState(DateTime.UtcNow).Wait();
}
// Changes after the scheduled time comes
private async Task ScheduledItemChangeState(DateTime scheduleFor)
{
using (var scope = Services.CreateScope())
{
var context =
scope.ServiceProvider
.GetRequiredService<DataContext>();
// Changing some data in database
}
}
public void Dispose()
{
_timer?.Dispose();
}
}
(item.ScheduledFor - DateTime.UtcNow) 作为 Timer 类构造函数的第三个参数传递以初始化一个新实例，实际上是要求计时器在我存储为 DateTime 的特定时间 item.ScheduledFor 中执行特定的工作。要查看完整的实现，请使用以下链接访问我的Github repo，它具有在重新启动服务器后从数据库中恢复定时任务的可能性：
https://github.com/aspian-io/aspian/tree/master/Infrastructure/Schedule
visibilityTimeout来指定消息对Dequeue和Peek操作不可见的时间。QueueClient theQueue = new QueueClient(connectionString, "mystoragequeue");
if (null != await theQueue.CreateIfNotExistsAsync())
{
//The queue was created...
}
var newPost = "Post Content Here";
var user_specified_datetime = new DateTime(2020, 9, 9, 20, 50, 25);
var datetime_now = DateTime.Now;
TimeSpan duration = user_specified_datetime.Subtract(datetime_now);
await theQueue.SendMessageAsync(newPost, duration, default);
services.AddDNTScheduler(options =>
{
// DNTScheduler needs a ping service to keep it alive. Set it to false if you don't need it. Its default value is true.
// options.AddPingTask = false;
options.AddScheduledTask<DoBackupTask>(
runAt: utcNow =>
{
var now = utcNow.AddHours(3.5);
return now.Hour == 14 && now.Minute == 08 && now.Second == 07;
},
order: 1);
});