“计时器+ Task.Run"；对比"while循环+ Task.Delay"在asp.net核心托管服务中 [英] "timer + Task.Run" vs "while loop + Task.Delay" in asp.net core hosted service
问题描述
我要求后台服务每天早上0:00运行 Process 方法.
I have a requirement that background service should run Process method every day at 0:00 a.m.
因此，我的团队成员之一编写了以下代码:
So, one of my team member wrote the following code:
public class MyBackgroundService : IHostedService, IDisposable
{
private readonly ILogger _logger;
private Timer _timer;
public MyBackgroundService(ILogger<MyBackgroundService> logger)
{
_logger = logger;
}
public void Dispose()
{
_timer?.Dispose();
}
public Task StartAsync(CancellationToken cancellationToken)
{
TimeSpan interval = TimeSpan.FromHours(24);
TimeSpan firstCall = DateTime.Today.AddDays(1).AddTicks(-1).Subtract(DateTime.Now);
Action action = () =>
{
Task.Delay(firstCall).Wait();
Process();
_timer = new Timer(
ob => Process(),
null,
TimeSpan.Zero,
interval
);
};
Task.Run(action);
return Task.CompletedTask;
}
public Task StopAsync(CancellationToken cancellationToken)
{
_timer?.Change(Timeout.Infinite, 0);
return Task.CompletedTask;
}
private Task Process()
{
try
{
// perform some database operations
}
catch (Exception e)
{
_logger.LogError(e, e.Message);
}
return Task.CompletedTask;
}
}
此代码可以正常工作.但是我不喜欢它同步等待直到第一次调用 Process ，所以线程被阻塞并且没有执行任何有用的工作(如果我错了，请纠正我).
This code works as expected. But I don't like that it synchronously waits till calling Process first time, so a thread is blocked and not performing any useful work (correct me if I am wrong).
我可以像这样使动作异步并在其中等待:
I could make an action async and await in it like this:
public Task StartAsync(CancellationToken cancellationToken)
{
// code omitted for brevity
Action action = async () =>
{
await Task.Delay(firstCall);
await Process();
// code omitted for brevity
}
但是我不确定在这里使用 Task.Run 是件好事，因为 Process 方法应该执行一些I/O操作(查询数据库并插入一些数据)，因为不建议在ASP.NET环境中使用 Task.Run .
But I am not sure that using Task.Run is a good thing here as Process method should perform some I/O operations (query DB and insert some data), and because it's not recommended to use Task.Run in ASP.NET environment.
我重构了 StartAsync 如下:
public async Task StartAsync(CancellationToken cancellationToken)
{
TimeSpan interval = TimeSpan.FromHours(24);
TimeSpan firstDelay = DateTime.Today.AddDays(1).AddTicks(-1).Subtract(DateTime.Now);
await Task.Delay(firstDelay);
while (!cancellationToken.IsCancellationRequested)
{
await Process();
await Task.Delay(interval, cancellationToken);
}
}
这使我根本不用在 MyBackgroundService 中使用计时器.
And this allows me not to use timer in MyBackgroundService at all.
我应该对"timer + Task.Run"使用第一种方法吗?或第二个带有"while循环+ Task.Delay"?
Should I use the first approach with "timer + Task.Run" or the second one with "while loop + Task.Delay"?
推荐答案
while 循环方法更简单，更安全.使用 Timer 该类有两个隐藏的陷阱:
The while loop approach is simpler and safer. Using the Timer class has two hidden gotchas:
