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调度程序后台服务中的异步计时器

background-service .net-core timer asynchronous c#

johnny 5 · 技术社区 · 7 年前

目前,我必须同步运行代码,如下所示:

public override Task StartAsync(CancellationToken cancellationToken)
{
    this._logger.LogInformation("Timed Background Service is starting.");

    this._timer = new Timer(ExecuteTask, null, TimeSpan.Zero,
        TimeSpan.FromSeconds(30));

    return Task.CompletedTask;
}

private void ExecuteTask(object state)
{
    this._logger.LogInformation("Timed Background Service is working.");
    using (var scope = _serviceProvider.CreateScope())
    {
        var coinbaseService = scope.ServiceProvider.GetRequiredService<CoinbaseService>();
        coinbaseService.FinalizeMeeting();
    }
}

e、 g(签署 timer.Elapsed (活动)

有没有一种方法可以在不执行fire和forget的情况下按定时计划利用异步代码

1 回复 | 直到 7 年前

g36 7 年前

对于那些正在寻找阻止同时运行任务的完整示例的人。基于@Gabriel Luci的回答和评论。

    /// <summary>
    /// Based on Microsoft.Extensions.Hosting.BackgroundService  https://github.com/aspnet/Extensions/blob/master/src/Hosting/Abstractions/src/BackgroundService.cs
    /// Additional info: - https://docs.microsoft.com/en-us/aspnet/core/fundamentals/host/hosted-services?view=aspnetcore-2.2&tabs=visual-studio#timed-background-tasks
    ///                  - https://stackoverflow.com/questions/53844586/async-timer-in-scheduler-background-service
    /// </summary>

    public abstract class TimedHostedService : IHostedService, IDisposable
    {
        private readonly ILogger _logger;
        private Timer _timer;
        private Task _executingTask;
        private readonly CancellationTokenSource _stoppingCts = new CancellationTokenSource();

        public TimedHostedService(ILogger<TimedHostedService> logger)
        {
            _logger = logger;
        }

        public Task StartAsync(CancellationToken cancellationToken)
        {
            _logger.LogInformation("Timed Background Service is starting.");

            _timer = new Timer(ExecuteTask, null, TimeSpan.FromSeconds(30), TimeSpan.FromMilliseconds(-1));

            return Task.CompletedTask;
        }

        private void ExecuteTask(object state)
        {
            _timer?.Change(Timeout.Infinite, 0);
            _executingTask = ExecuteTaskAsync(_stoppingCts.Token);
        }

        private async Task ExecuteTaskAsync(CancellationToken stoppingToken)
        {
            await RunJobAsync(stoppingToken);
            _timer.Change(TimeSpan.FromSeconds(30), TimeSpan.FromMilliseconds(-1));
        }

        /// <summary>
        /// This method is called when the <see cref="IHostedService"/> starts. The implementation should return a task 
        /// </summary>
        /// <param name="stoppingToken">Triggered when <see cref="IHostedService.StopAsync(CancellationToken)"/> is called.</param>
        /// <returns>A <see cref="Task"/> that represents the long running operations.</returns>
        protected abstract Task RunJobAsync(CancellationToken stoppingToken);

        public virtual async Task StopAsync(CancellationToken cancellationToken)
        {
            _logger.LogInformation("Timed Background Service is stopping.");
            _timer?.Change(Timeout.Infinite, 0);

            // Stop called without start
            if (_executingTask == null)
            {
                return;
            }

            try
            {
                // Signal cancellation to the executing method
                _stoppingCts.Cancel();
            }
            finally
            {
                // Wait until the task completes or the stop token triggers
                await Task.WhenAny(_executingTask, Task.Delay(Timeout.Infinite, cancellationToken));
            }

        }

        public void Dispose()
        {
            _stoppingCts.Cancel();
            _timer?.Dispose();
        }
    }

Gabriel Luci 7 年前

目的 async 就是不占用主线程。但这已经是一个后台线程了,所以这并不重要,除非它是一个ASP.NET核心应用程序。这是唯一重要的一次,因为线程池是有限的,耗尽线程池意味着无法处理更多的请求。

异步的 异步的

private async void ExecuteTask(object state)
{
    //await stuff here
}

是的,我知道你说你不想“开火然后忘记”,但是 ExecuteTask 方法将被调用,并且不关心(或检查)它是否(1)仍在运行或(2)是否失败。 这是真的,无论你运行这个或者不是。

执行任务 a中的方法 try / catch 阻止并确保它记录在某个地方,以便您知道发生了什么。

另一个问题是知道它是否还在运行(这也是一个问题,即使你没有运行) 异步的 ).还有一种方法可以缓解这种情况:

private Task doWorkTask;

private void ExecuteTask(object state)
{
    doWorkTask = DoWork();
}

private async Task DoWork()
{
    //await stuff here
}

Task . 这将允许您检查服务器的状态 任务 代码中的任何其他地方。例如,如果要验证是否已完成,可以查看 doWorkTask.IsCompleted 或 doWorkTask.Status .

此外,当应用程序关闭时,您可以使用:

await doWorkTask;

在关闭应用程序之前确保任务已完成。否则,线程将被终止,可能使事情处于不一致的状态。请注意,使用 await doWorkTask DoWork() .

在开始下一个任务之前,最好先验证上一个任务是否已完成。

Seagull 5 年前

这是一个基于先前回答的改进版本。改进:

对于执行的每个任务,都会创建一个作用域,因此您可以访问RunJobAsync中的任何作用域服务
可以在继承的类中指定间隔和初始任务执行时间。

访问作用域服务示例

    protected override async Task RunJobAsync(IServiceProvider serviceProvider, CancellationToken stoppingToken)
    {
            DbContext context = serviceProvider.GetRequiredService<DbContext>();
    }

源代码:

public abstract class TimedHostedService : IHostedService, IDisposable
{
    private readonly ILogger _logger;
    private Timer _timer;
    private Task _executingTask;
    private readonly CancellationTokenSource _stoppingCts = new CancellationTokenSource();

    IServiceProvider _services;
    public TimedHostedService(IServiceProvider services)
    {
        _services = services;
        _logger = _services.GetRequiredService<ILogger<TimedHostedService>>();
        
    }

    public Task StartAsync(CancellationToken cancellationToken)
    {
        _timer = new Timer(ExecuteTask, null,FirstRunAfter, TimeSpan.FromMilliseconds(-1));

        return Task.CompletedTask;
    }

    private void ExecuteTask(object state)
    {
        _timer?.Change(Timeout.Infinite, 0);
        _executingTask = ExecuteTaskAsync(_stoppingCts.Token);
    }

    private async Task ExecuteTaskAsync(CancellationToken stoppingToken)
    {
        try
        {
            using (var scope = _services.CreateScope())
            {
                await RunJobAsync(scope.ServiceProvider, stoppingToken);
            }
        }
        catch (Exception exception)
        {
            _logger.LogError("BackgroundTask Failed", exception);
        }
        _timer.Change(Interval, TimeSpan.FromMilliseconds(-1));
    }

    /// <summary>
    /// This method is called when the <see cref="IHostedService"/> starts. The implementation should return a task 
    /// </summary>
    /// <param name="serviceProvider"></param>
    /// <param name="stoppingToken">Triggered when <see cref="IHostedService.StopAsync(CancellationToken)"/> is called.</param>
    /// <returns>A <see cref="Task"/> that represents the long running operations.</returns>
    protected abstract Task RunJobAsync(IServiceProvider serviceProvider, CancellationToken stoppingToken);
    protected abstract TimeSpan Interval { get; }
    
    protected abstract TimeSpan FirstRunAfter { get; }
    
    public virtual async Task StopAsync(CancellationToken cancellationToken)
    {
        _timer?.Change(Timeout.Infinite, 0);

        // Stop called without start
        if (_executingTask == null)
        {
            return;
        }

        try
        {
            // Signal cancellation to the executing method
            _stoppingCts.Cancel();
        }
        finally
        {
            // Wait until the task completes or the stop token triggers
            await Task.WhenAny(_executingTask, Task.Delay(Timeout.Infinite, cancellationToken));
        }

    }

    public void Dispose()
    {
        _stoppingCts.Cancel();
        _timer?.Dispose();
    }
}