Question

我们正在使用.NET运行Web场。每个Web服务器在其内存中都包含大量静态对象。 Gen 2垃圾收集（GC）需要10-20秒，每5分钟运行一次。我们或多或少地遇到了StackOverflow遇到的相同问题：http://samsaffron.com/archive/2011/10/28/in-managed-code-we-trust-our-recent-battles-with-the-net-garbage-collector

目前，我们正在减少缓存中的对象数量。但是，这需要时间。

与此同时，我们实施了记录here的方法，以便在.NET中收到关于接近GC的通知。目标是在GC接近时将Web服务器从服务器场中取出，并在GC结束后将其包含在服务器场中。但是，我们只收到所有GC的0.7％的通知。我们使用maxGenerationThreshold和largeObjectHeapThreshold为8.我们尝试了其他阈值，但错过的GC数量没有变化。

我们正在使用并发服务器垃圾回收（http://msdn.microsoft.com/en-us/library/ms229357.aspx）。 GCLatencyMode是Interactive（请参阅http://msdn.microsoft.com/en-us/library/system.runtime.gclatencymode.aspx）。在这里，我们再次尝试使用其他GC模式（工作站模式，批处理等）。我们再次没有收到大多数GC的通知。

我们做错了什么，或者是否无法获得每个GC的通知？我们如何增加通知数量？

根据http://assets.red-gate.com/community/books/assets/Under_the_Hood_of_.NET_Management.pdf，当Gen2达到~10 MB时，会在开始时触发GC。我们有很多RAM，因此如果我们可以手动将此阈值设置为更高的级别，则需要更多时间才能达到此阈值，并且根据我的理解，获取通知的概率会增加。有没有办法修改这个阈值？

这是注册和侦听通知的代码：

GC.RegisterForFullGCNotification(gcThreshold, gcThreshold);
// Start a thread using WaitForFullGCProc.
thWaitForFullGC = new Thread(WaitForFullGCProc);
thWaitForFullGC.Name = "HealthTestGCNotificationListenerThread (Threshold=" + gcThreshold + ")";
thWaitForFullGC.IsBackground = true;

WaitForFullGCProc（）：

    private void WaitForFullGCProc()
{
    try
    {
        while (!gcAbort)
        {
            // Check for a notification of an approaching collection.
            GCNotificationStatus s;
            do
            {
                int timeOut = CheckForMissedGc() > 0 ? 5000 : (10 * 60 * 1000);
                s = GC.WaitForFullGCApproach(timeOut);
                if (this.GcState == GCState.InducedUnnotified)
                {
                    // Set the GcState back to okay to prevent the message from staying in the ApplicationMonitoring.
                    this.GcState = GCState.Okay;
                }
            } while (s == GCNotificationStatus.Timeout);

            if (s == GCNotificationStatus.Succeeded)
            {
                SetGcState(GCState.Approaching, "GC is approaching..");
                gcApproachNotificationCount++;
            }
            else
            {
                ...
            }

            Stopwatch stopwatch = Stopwatch.StartNew();
            s = GC.WaitForFullGCComplete((int)PrewarnTime.TotalMilliseconds);
            long elapsed = stopwatch.ElapsedMilliseconds;

            if (s == GCNotificationStatus.Timeout)
            {
                if (this.ForceGCWhenApproaching && !this.IsInGc && !this.IsPeriodicGcApproaching)
                {
                    this.IsInGc = true;
                    GC.Collect(GC.MaxGeneration, GCCollectionMode.Forced, blocking: true);
                    GC.WaitForPendingFinalizers();
                    elapsed = stopwatch.ElapsedMilliseconds;
                    this.IsInGc = false;
                }
            }
        }
        gcAbort = false;
    }
    catch (Exception e)
    {
    }
}

Answer 1

注意：这不仅仅是一个评论，还包括一个大型代码示例。

您是否曾考虑尝试通过其他方式获取GC通知？ Jeffrey Richter（通过C＃CLR）解释了一种获取通知的好方法，它使用一个对象并在它的生成代码中检查它的终结器方法。

这是类：它使用内部对象，如果提供的代数匹配（例如，请参见new GenObject(0);）或者为下一代更高代复活，则会收集内部对象。

您只需使用GCNotification.GCDone += GCDoneHandler;

订阅即可

 public static class GCNotification
    {
        private static Action<Int32> s_gcDone = null; // The event's field
        public static event Action<Int32> GCDone
        {
            add
            {
                // If there were no registered delegates before, start reporting notifications now
                if (s_gcDone == null) { new GenObject(0); new GenObject(1); new GenObject(2); }
                s_gcDone += value;
            }
            remove { s_gcDone -= value; }
        }
        private sealed class GenObject
        {
            private Int32 m_generation;
            public GenObject(Int32 generation) { m_generation = generation; }
            ~GenObject()
            { // This is the Finalize method
                // If this object is in the generation we want (or higher),
                // notify the delegates that a GC just completed
                if (GC.GetGeneration(this) >= m_generation)
                {
                    Action<Int32> temp = Volatile.Read(ref s_gcDone);
                    if (temp != null) temp(m_generation);
                }
                // Keep reporting notifications if there is at least one delegate registered,
                // the AppDomain isn't unloading, and the process isn’t shutting down
                if ((s_gcDone != null)
                && !AppDomain.CurrentDomain.IsFinalizingForUnload()
                && !Environment.HasShutdownStarted)
                {
                    // For Gen 0, create a new object; for Gen 2, resurrect the object
                    // & let the GC call Finalize again the next time Gen 2 is GC'd
                    if (m_generation == 0) new GenObject(0);
                    else GC.ReRegisterForFinalize(this);
                }
                else { /* Let the objects go away */ }
            }
        }
    }

错过垃圾收集通知

1 个答案: