后台服务中的 Task.Run 意外停止工作

Posted 2023-04-12

【中文标题】后台服务中的 Task.Run 意外停止工作

【英文标题】：Task.Run inside backgroundservice unexpectedly stops working

【发布时间】：2020-12-14 00:16:57

【问题描述】：

我在后台服务中使用 Task.Run。我有后台服务，负责特定系统的登录和发送心跳。

public class TestBGService : IHostedService

    private readonly ITestService _testService;
    private bool MustLogOn  get; set;  = true;
    private string id  get; set; 
    public TestBGService(ITestService testService)
    
        _testService = testService;
    

    public async Task StartAsync(CancellationToken cancellationToken)
    
        while (!cancellationToken.IsCancellationRequested)
        
            Log.Information("TestBGService starts Initialize");
            await Initialize();
        
    

    public Task StopAsync(CancellationToken cancellationToken)
    
        return Task.CompletedTask;
    

    private async Task Initialize()
    
        try
        
            if (MustLogOn)
            
                Log.Information("TestBGService ExecuteAsync trying to LogOnAsync");
                id = await _testService.LogOnAsync();
                if (!string.IsNullOrEmpty(id))
                
                    Log.Information($"new id equals to id");
                    MustLogOn = false;

                    _ = Task.Run(async () =>
                     
                         while (true)
                         
                             bool res = await SendHeartBeat(id);
                             Log.Information($"res from SendHeartBeat res");
                             if (!res)
                             
                                 break;
                             
                             await Task.Delay(10000);
                         
                     );
                    await _testService.StartProcessAsync(id);
                
            
        
        catch (Exception ex)
        
            Log.Error($"TestBGService ExecuteAsync throws ex.ToString()");
        
    


    private async Task<bool> SendHeartBeat(string id)
    
        bool isSuccess = true;
        try
        
            Log.Information("TestBGService sending heartbeat at " + DateTime.Now);
            var response = new HeartBeatResponseModel();
            response = await _testService.SendHeartBeatAsync(id);
            Log.Information("TestBGService heartbeat response equals to " + response.IsSuccessful);
            if (!response.IsSuccessful)
            
                MustLogOn = true;
                isSuccess = response.IsSuccessful;
            
        
        catch (Exception ex)
        
            Log.Error(ex, "TestBGService SendHeartBeat throws");
            isSuccess = false;
            MustLogOn = true;
        
        return isSuccess;
    

Initialize 方法尝试LogOn 到系统，在成功的情况下，它需要启动SendHeartBeat。 SendHeartBeat 方法负责获取成功或失败。如果成功，我将 MustLogon 的值更改为 false 并每 10 秒发送一次 SendHeartBeat。 SendHeartBeat 的并行我需要调用_testService.StartProcessAsync 从流中获取数据。不知何故它停止工作并再次启动 LogOn 但我需要它直到它返回 false 它应该工作并且 SendHeartBeat 需要每 10 秒完成一次但不幸的是，它在 bool res = true 的情况下停止工作并且此刻它不会抛出任何例外。有什么建议吗？

【问题讨论】：

看看这个例子：docs.microsoft.com/en-us/aspnet/core/fundamentals/host/… 并尝试相应地修改您的代码。你不应该永远在 StartAsync 方法中徘徊。

Fildor，当我发送cancellationToken时它停止

是的，因为这是垃圾（抱歉）。请查看定时服务应该如何工作（请参阅第一条评论中的链接）。在 Timer Callback 中： 1. 如果需要，请登录， 2. SendHeartBeat。完毕。不要从任务中开始任务...

或者您可以从提供的链接@Fildor 中快速使用BackgroundService，将您的“Initialize”逻辑移动到ExecuteAsync（并删除Task.Run 这里有什么意义?)。

没有什么能阻止你这样做。

【参考方案1】：

这是我在BackgroundService base class 的链接之后想出的，并“插入”您所需的功能：（当然，未经测试）

public class TestBGService : BackGroundService

    // I guess you are using different logging
    private readonly ILogger<TestBGService> _logger; 
    // Your service to send Heartbeats to
    private readonly ITestService _testService;
    // If id is null, we need to login.
    private string _id = null;

    public TestBGService (ILogger<TestBGService> logger, ITestService testService)
    
        _logger = logger;
        _testService = testService ?? throw new ArgumentNullException(nameof(testService));
    

    public Task StartAsync(CancellationToken stoppingToken)
    
        _logger.LogInformation("TestBGService  running.");
        return Task.CompletedTask;
    

    // This will be triggered by the runtime.
    private async Task ExecuteAsync (System.Threading.CancellationToken stoppingToken)
    
        while( !stoppingToken.CancellationRequested )
        
            try
            
                if( string.IsNullOrEmpty(_id) )
                 
                     // _id is null => perform login
                     _id = await _testService.LogOnAsync(); // perhaps pass stoppingToken?
                
                bool res = await SendHeartBeat(id); // again: consider passing stoppingToken
                if( !res ) _id = null; // Heartbeat unsuccessful: login next time
                await Task.Delay(TimeSpan.FromSeconds(10), stoppingToken);
            
            catch(Exception ex) // You should actually catch more specific exceptions.
            
                // TODO log Exception
                _id = null; // Reset id, so we login next time.
            

        
    

    private async Task<bool> SendHeartBeat(string id)
    
        // Don't even try if login was unsuccessful.
        if ( string.IsNullOrEmpty(id) ) return false;

        _logger.LogInformation("TestBGService sending heartbeat at 0" , DateTime.Now);
        var response = await _testService.SendHeartBeatAsync(id);
        _logger.LogInformation("TestBGService heartbeat response 0successful", response.IsSuccessful ? "" : "un");
        return response.IsSuccessful;
    

    public Task StopAsync(CancellationToken stoppingToken)
    
        _logger.LogInformation("TestBGService  is stopping.");
        // TODO maybe explicit logout?
        return Task.CompletedTask;