Question

我正在尝试为Windows服务（已通过InstallUtil.exe安装）创建后台任务，并使用 SynchronizationContext 将一些消息发送到主服务线程。

不幸的是，SynchronizationContext.Current在服务启动时始终是null。

我已经看到了有关该主题的一些问题，并暗示了为什么在各种情况下（例如Winforms，WPF应用程序中）SynchronizationContext为null，却对Windows服务一无所知。

如何解决此问题？代码下方：

using Lextm.SharpSnmpLib.Messaging;
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Diagnostics;
using System.IO;
using System.Linq;
using System.Net;
using System.ServiceProcess;
using System.Text;
using System.Threading;
using System.Threading.Tasks;

namespace SnmpTrapListenerService
{
    public partial class SnmpTrapListenerService : ServiceBase
    {
        public Listener Listener { get; set; }
        public CancellationTokenSource CancellationTokenSource { get; set; }
        public Task PulseTask { get; set; }
        public SynchronizationContext SyncContext { get; set; }

        public SnmpTrapListenerService()
        {
            //Debugging windows service.  
            Debugger.Launch();
            InitializeComponent();
            Debug.WriteLine($"Main service threadId: {Thread.CurrentThread.ManagedThreadId}");
        }

        protected override void OnStart(string[] args)
        {
            try
            {
                CancellationTokenSource = new CancellationTokenSource();
                SyncContext = SynchronizationContext.Current; //Here I'm getting always null.
                PulseTask = new Task(x =>
                {
                    Debug.WriteLine($"Pulse task threadId: {Thread.CurrentThread.ManagedThreadId}");
                    while (true)
                    {
                        var context = (SynchronizationContext)x;
                        context.Post(new SendOrPostCallback(y => DoSomethingOnServiceMainThread()), null);
                        Debug.WriteLine($"Alive at {DateTime.Now.ToLongTimeString()}");
                        Thread.Sleep(5000);
                    }
                }, SyncContext, CancellationTokenSource.Token);

                PulseTask.Start();

                Listener = new Listener();
                Listener.AddBinding(new IPEndPoint(IPAddress.Parse("127.0.0.1"), 162)); //IP address of listener system  
                Listener.MessageReceived += Listener_MessageReceived;
                Listener.StartAsync();
            }
            catch (Exception ex)
            {
                Debug.WriteLine(ex.Message);
            }
            Debug.WriteLine("Service started");
        }
        private static void Listener_MessageReceived(object sender, MessageReceivedEventArgs e)
        {
            File.AppendAllText("servicelog.log", "Version :" + e.Message.Version + "\n");
            File.AppendAllText("servicelog.log", "Version :" + e.Message.Scope.Pdu.Variables[4].Data.ToString() + "\n");
        }

        protected override void OnStop()
        {
            CancellationTokenSource.Cancel();
            Listener.Stop();
            Debug.WriteLine("Service stopped");
        }

        private void DoSomethingOnServiceMainThread() 
        {
            //Some work that needs to be done one Service main thread.
        }
    }
}

Answer 1

控制台和服务应用程序没有默认的SynchronizationContext。这是因为没有“ UI”线程在应用程序运行时不断地抽取消息。

问题是为什么您需要同步上下文？

WindowsService的OnStart方法中SynchronizationContext为null

1 个答案: