垃圾回收通知
在有些情况下，公共语言运行时执行的完整垃圾回收（即第 2 代回收）可能会对性能产生负面影响。 特别是，处理大量请求的服务器可能会出现此问题；在这种情况下，长时间垃圾回收会导致请求超时。为了防止在关键时期发生完全回收，可以接收即将执行完全垃圾回收的通知，再采取措施将工作负载重定向到另一个服务器实例。 也可以自行诱导回收，前提是当前服务器实例不需要处理请求。
RegisterForFullGCNotification 方法注册为，在运行时检测到即将执行完全垃圾回收时发出通知。 此通知分为两个部分：完全垃圾回收何时即将执行，以及完全垃圾回收何时完成。
警告
当启用了 <gcConcurrent> 配置元素时，如果整个 GC 是作为后台 GC 完成的，WaitForFullGCComplete 可能会返回 NotApplicableGCNotificationStatus。
若要确定何时发出通知，请使用 WaitForFullGCApproach 和 WaitForFullGCComplete 方法。 通常，在 while 循环中使用这些方法，以持续获取表示通知状态的 GCNotificationStatus 枚举。 如果值为 Succeeded，可以执行下列操作：
为了响应使用 WaitForFullGCApproach 方法获得的通知，可以重定向工作负载，并能自行诱导回收。
为了响应使用 WaitForFullGCComplete 方法获得的通知，可以让当前服务器实例再次用于处理请求。 也可以收集信息。 例如，可以使用 CollectionCount 方法记录回收次数。
WaitForFullGCApproach 和 WaitForFullGCComplete 方法要配合使用。 使用一个方法，而不使用另一个方法，可能会生成不确定的结果。
完全垃圾回收
如果发生下列任一情况，运行时就会执行完全垃圾回收：
足够多的内存已提升到第 2 代，导致执行下一个第 2 代回收。
足够多的内存已提升到大型对象堆，导致执行下一个第 2 代回收。
由于其他因素，导致第 1 代回收升级为第 2 代回收。
在 RegisterForFullGCNotification 方法中指定的阈值适用于前两种情况。 不过，在第一种情况下，不一定会在与指定的阈值相称的时间收到通知，原因有下面两个：
运行时不检查每个小型对象分配（出于性能考虑）。
只有第 1 代回收将内存提升到第 2 代。
第三种情况也加剧了通知接收时间的不确定性。 可以在此期间重定向请求，或在可以更好适应时自行诱导回收，从而减轻不合时宜的完全垃圾回收造成的影响。尽管并不保证有效，但确实证明这是非常实用的方法。
通知阈值参数
RegisterForFullGCNotification 方法包含两个参数，用于指定第 2 代对象和大型对象堆的阈值。 如果达到这些值，就应发出垃圾回收通知。 下表介绍了这些参数。
| 参数 | 描述 |
|---|---|
maxGenerationThreshold |
介于 1 和 99 之间的数字，指定根据在第 2 代中提升的对象，应何时发出通知。 |
largeObjectHeapThreshold |
介于 1 和 99 之间的数字，指定根据大型对象堆中分配的对象，应何时发出通知。 |
如果指定的值过高，很可能会出现的情况是，将会收到通知，但在运行时执行回收前等待的时间太长。 如果自行诱导回收，回收的对象可能会多于在运行时执行回收时回收的对象。
如果指定的值过低，在运行时执行回收前等待通知的时间可能不够长。
示例
描述
在下面的示例中，一组服务器处理传入的 Web 请求。 为了模拟处理请求的工作负载，将字节数组添加到 List<T> 集合中。 每个服务器都会注册获取垃圾回收通知，再对 WaitForFullGCProc 用户方法启动线程，以持续监视 WaitForFullGCApproach 和 WaitForFullGCComplete 方法返回的 GCNotificationStatus 枚举。
在通知发出时，WaitForFullGCApproach 和 WaitForFullGCComplete 方法调用它们各自的事件处理用户方法：
OnFullGCApproachNotify此方法调用
RedirectRequests用户方法，指示请求队列服务器暂停向服务器发送请求。 具体模拟方式是，将类级别变量bAllocate设置为false，这样就不会再分配对象。接下来，调用
FinishExistingRequests用户方法，完成处理挂起的服务器请求。 具体模拟方式是，清除 List<T> 集合。最后，由于工作负载很轻，诱导垃圾回收。
OnFullGCCompleteNotify此方法调用用户方法
AcceptRequests以继续接受请求，因为服务器不再易受完全垃圾回收影响。 此操作的具体模拟方式是，将bAllocate变量设置为true，以便能够继续将对象添加到 List<T> 集合。
下面的代码包含示例的 Main 方法。
using namespace System;
using namespace System::Collections::Generic;
using namespace System::Threading;
namespace GCNotify
{
ref class Program
{
private:
// Variable for continual checking in the
// While loop in the WaitForFullGCProc method.
static bool checkForNotify = false;
// Variable for suspending work
// (such servicing allocated server requests)
// after a notification is received and then
// resuming allocation after inducing a garbage collection.
static bool bAllocate = false;
// Variable for ending the example.
static bool finalExit = false;
// Collection for objects that
// simulate the server request workload.
static List<array<Byte>^>^ load = gcnew List<array<Byte>^>();
public:
static void Main()
{
try
{
// Register for a notification.
GC::RegisterForFullGCNotification(10, 10);
Console::WriteLine("Registered for GC notification.");
checkForNotify = true;
bAllocate = true;
// Start a thread using WaitForFullGCProc.
Thread^ thWaitForFullGC = gcnew Thread(gcnew ThreadStart(&WaitForFullGCProc));
thWaitForFullGC->Start();
// While the thread is checking for notifications in
// WaitForFullGCProc, create objects to simulate a server workload.
try
{
int lastCollCount = 0;
int newCollCount = 0;
while (true)
{
if (bAllocate)
{
load->Add(gcnew array<Byte>(1000));
newCollCount = GC::CollectionCount(2);
if (newCollCount != lastCollCount)
{
// Show collection count when it increases:
Console::WriteLine("Gen 2 collection count: {0}", GC::CollectionCount(2).ToString());
lastCollCount = newCollCount;
}
// For ending the example (arbitrary).
if (newCollCount == 500)
{
finalExit = true;
checkForNotify = false;
break;
}
}
}
}
catch (OutOfMemoryException^)
{
Console::WriteLine("Out of memory.");
}
finalExit = true;
checkForNotify = false;
GC::CancelFullGCNotification();
}
catch (InvalidOperationException^ invalidOp)
{
Console::WriteLine("GC Notifications are not supported while concurrent GC is enabled.\n"
+ invalidOp->Message);
}
}
public:
static void OnFullGCApproachNotify()
{
Console::WriteLine("Redirecting requests.");
// Method that tells the request queuing
// server to not direct requests to this server.
RedirectRequests();
// Method that provides time to
// finish processing pending requests.
FinishExistingRequests();
// This is a good time to induce a GC collection
// because the runtime will induce a full GC soon.
// To be very careful, you can check precede with a
// check of the GC.GCCollectionCount to make sure
// a full GC did not already occur since last notified.
GC::Collect();
Console::WriteLine("Induced a collection.");
}
public:
static void OnFullGCCompleteEndNotify()
{
// Method that informs the request queuing server
// that this server is ready to accept requests again.
AcceptRequests();
Console::WriteLine("Accepting requests again.");
}
public:
static void WaitForFullGCProc()
{
while (true)
{
// CheckForNotify is set to true and false in Main.
while (checkForNotify)
{
// Check for a notification of an approaching collection.
GCNotificationStatus s = GC::WaitForFullGCApproach();
if (s == GCNotificationStatus::Succeeded)
{
Console::WriteLine("GC Notification raised.");
OnFullGCApproachNotify();
}
else if (s == GCNotificationStatus::Canceled)
{
Console::WriteLine("GC Notification cancelled.");
break;
}
else
{
// This can occur if a timeout period
// is specified for WaitForFullGCApproach(Timeout)
// or WaitForFullGCComplete(Timeout)
// and the time out period has elapsed.
Console::WriteLine("GC Notification not applicable.");
break;
}
// Check for a notification of a completed collection.
s = GC::WaitForFullGCComplete();
if (s == GCNotificationStatus::Succeeded)
{
Console::WriteLine("GC Notification raised.");
OnFullGCCompleteEndNotify();
}
else if (s == GCNotificationStatus::Canceled)
{
Console::WriteLine("GC Notification cancelled.");
break;
}
else
{
// Could be a time out.
Console::WriteLine("GC Notification not applicable.");
break;
}
}
Thread::Sleep(500);
// FinalExit is set to true right before
// the main thread cancelled notification.
if (finalExit)
{
break;
}
}
}
private:
static void RedirectRequests()
{
// Code that sends requests
// to other servers.
// Suspend work.
bAllocate = false;
}
static void FinishExistingRequests()
{
// Code that waits a period of time
// for pending requests to finish.
// Clear the simulated workload.
load->Clear();
}
static void AcceptRequests()
{
// Code that resumes processing
// requests on this server.
// Resume work.
bAllocate = true;
}
};
}
int main()
{
GCNotify::Program::Main();
}
public static void Main(string[] args)
{
try
{
// Register for a notification.
GC.RegisterForFullGCNotification(10, 10);
Console.WriteLine("Registered for GC notification.");
checkForNotify = true;
bAllocate = true;
// Start a thread using WaitForFullGCProc.
Thread thWaitForFullGC = new Thread(new ThreadStart(WaitForFullGCProc));
thWaitForFullGC.Start();
// While the thread is checking for notifications in
// WaitForFullGCProc, create objects to simulate a server workload.
try
{
int lastCollCount = 0;
int newCollCount = 0;
while (true)
{
if (bAllocate)
{
load.Add(new byte[1000]);
newCollCount = GC.CollectionCount(2);
if (newCollCount != lastCollCount)
{
// Show collection count when it increases:
Console.WriteLine("Gen 2 collection count: {0}", GC.CollectionCount(2).ToString());
lastCollCount = newCollCount;
}
// For ending the example (arbitrary).
if (newCollCount == 500)
{
finalExit = true;
checkForNotify = false;
break;
}
}
}
}
catch (OutOfMemoryException)
{
Console.WriteLine("Out of memory.");
}
finalExit = true;
checkForNotify = false;
GC.CancelFullGCNotification();
}
catch (InvalidOperationException invalidOp)
{
Console.WriteLine("GC Notifications are not supported while concurrent GC is enabled.\n"
+ invalidOp.Message);
}
}
Imports System.Collections.Generic
Imports System.Threading
Class Program
' Variables for continual checking in the
' While loop in the WaitForFullGcProc method.
Private Shared checkForNotify As Boolean = False
' Variable for suspending work
' (such as servicing allocated server requests)
' after a notification is received and then
' resuming allocation after inducing a garbage collection.
Private Shared bAllocate As Boolean = False
' Variable for ending the example.
Private Shared finalExit As Boolean = False
' Collection for objects that
' simulate the server request workload.
Private Shared load As New List(Of Byte())
Public Shared Sub Main(ByVal args() As String)
Try
' Register for a notification.
GC.RegisterForFullGCNotification(10, 10)
Console.WriteLine("Registered for GC notification.")
bAllocate = True
checkForNotify = True
' Start a thread using WaitForFullGCProc.
Dim thWaitForFullGC As Thread = _
New Thread(New ThreadStart(AddressOf WaitForFullGCProc))
thWaitForFullGC.Start()
' While the thread is checking for notifications in
' WaitForFullGCProc, create objects to simulate a server workload.
Try
Dim lastCollCount As Integer = 0
Dim newCollCount As Integer = 0
While (True)
If bAllocate = True Then
load.Add(New Byte(1000) {})
newCollCount = GC.CollectionCount(2)
If (newCollCount <> lastCollCount) Then
' Show collection count when it increases:
Console.WriteLine("Gen 2 collection count: {0}", _
GC.CollectionCount(2).ToString)
lastCollCount = newCollCount
End If
' For ending the example (arbitrary).
If newCollCount = 500 Then
finalExit = True
checkForNotify = False
bAllocate = False
Exit While
End If
End If
End While
Catch outofMem As OutOfMemoryException
Console.WriteLine("Out of memory.")
End Try
finalExit = True
checkForNotify = False
GC.CancelFullGCNotification()
Catch invalidOp As InvalidOperationException
Console.WriteLine("GC Notifications are not supported while concurrent GC is enabled." _
& vbLf & invalidOp.Message)
End Try
End Sub
Public Shared Sub OnFullGCApproachNotify()
Console.WriteLine("Redirecting requests.")
' Method that tells the request queuing
' server to not direct requests to this server.
RedirectRequests()
' Method that provides time to
' finish processing pending requests.
FinishExistingRequests()
' This is a good time to induce a GC collection
' because the runtime will induce a ful GC soon.
' To be very careful, you can check precede with a
' check of the GC.GCCollectionCount to make sure
' a full GC did not already occur since last notified.
GC.Collect()
Console.WriteLine("Induced a collection.")
End Sub
Public Shared Sub OnFullGCCompleteEndNotify()
' Method that informs the request queuing server
' that this server is ready to accept requests again.
AcceptRequests()
Console.WriteLine("Accepting requests again.")
End Sub
Public Shared Sub WaitForFullGCProc()
While True
' CheckForNotify is set to true and false in Main.
While checkForNotify
' Check for a notification of an approaching collection.
Dim s As GCNotificationStatus = GC.WaitForFullGCApproach
If (s = GCNotificationStatus.Succeeded) Then
Console.WriteLine("GC Notification raised.")
OnFullGCApproachNotify()
ElseIf (s = GCNotificationStatus.Canceled) Then
Console.WriteLine("GC Notification cancelled.")
Exit While
Else
' This can occur if a timeout period
' is specified for WaitForFullGCApproach(Timeout)
' or WaitForFullGCComplete(Timeout)
' and the time out period has elapsed.
Console.WriteLine("GC Notification not applicable.")
Exit While
End If
' Check for a notification of a completed collection.
s = GC.WaitForFullGCComplete
If (s = GCNotificationStatus.Succeeded) Then
Console.WriteLine("GC Notification raised.")
OnFullGCCompleteEndNotify()
ElseIf (s = GCNotificationStatus.Canceled) Then
Console.WriteLine("GC Notification cancelled.")
Exit While
Else
' Could be a time out.
Console.WriteLine("GC Notification not applicable.")
Exit While
End If
End While
Thread.Sleep(500)
' FinalExit is set to true right before
' the main thread cancelled notification.
If finalExit Then
Exit While
End If
End While
End Sub
Private Shared Sub RedirectRequests()
' Code that sends requests
' to other servers.
' Suspend work.
bAllocate = False
End Sub
Private Shared Sub FinishExistingRequests()
' Code that waits a period of time
' for pending requests to finish.
' Clear the simulated workload.
load.Clear()
End Sub
Private Shared Sub AcceptRequests()
' Code that resumes processing
' requests on this server.
' Resume work.
bAllocate = True
End Sub
End Class
下面的代码包含 WaitForFullGCProc 用户方法，其中包括持续 while 循环，用于检查是否有垃圾回收通知。
public:
static void WaitForFullGCProc()
{
while (true)
{
// CheckForNotify is set to true and false in Main.
while (checkForNotify)
{
// Check for a notification of an approaching collection.
GCNotificationStatus s = GC::WaitForFullGCApproach();
if (s == GCNotificationStatus::Succeeded)
{
Console::WriteLine("GC Notification raised.");
OnFullGCApproachNotify();
}
else if (s == GCNotificationStatus::Canceled)
{
Console::WriteLine("GC Notification cancelled.");
break;
}
else
{
// This can occur if a timeout period
// is specified for WaitForFullGCApproach(Timeout)
// or WaitForFullGCComplete(Timeout)
// and the time out period has elapsed.
Console::WriteLine("GC Notification not applicable.");
break;
}
// Check for a notification of a completed collection.
s = GC::WaitForFullGCComplete();
if (s == GCNotificationStatus::Succeeded)
{
Console::WriteLine("GC Notification raised.");
OnFullGCCompleteEndNotify();
}
else if (s == GCNotificationStatus::Canceled)
{
Console::WriteLine("GC Notification cancelled.");
break;
}
else
{
// Could be a time out.
Console::WriteLine("GC Notification not applicable.");
break;
}
}
Thread::Sleep(500);
// FinalExit is set to true right before
// the main thread cancelled notification.
if (finalExit)
{
break;
}
}
}
public static void WaitForFullGCProc()
{
while (true)
{
// CheckForNotify is set to true and false in Main.
while (checkForNotify)
{
// Check for a notification of an approaching collection.
GCNotificationStatus s = GC.WaitForFullGCApproach();
if (s == GCNotificationStatus.Succeeded)
{
Console.WriteLine("GC Notification raised.");
OnFullGCApproachNotify();
}
else if (s == GCNotificationStatus.Canceled)
{
Console.WriteLine("GC Notification cancelled.");
break;
}
else
{
// This can occur if a timeout period
// is specified for WaitForFullGCApproach(Timeout)
// or WaitForFullGCComplete(Timeout)
// and the time out period has elapsed.
Console.WriteLine("GC Notification not applicable.");
break;
}
// Check for a notification of a completed collection.
GCNotificationStatus status = GC.WaitForFullGCComplete();
if (status == GCNotificationStatus.Succeeded)
{
Console.WriteLine("GC Notification raised.");
OnFullGCCompleteEndNotify();
}
else if (status == GCNotificationStatus.Canceled)
{
Console.WriteLine("GC Notification cancelled.");
break;
}
else
{
// Could be a time out.
Console.WriteLine("GC Notification not applicable.");
break;
}
}
Thread.Sleep(500);
// FinalExit is set to true right before
// the main thread cancelled notification.
if (finalExit)
{
break;
}
}
}
Public Shared Sub WaitForFullGCProc()
While True
' CheckForNotify is set to true and false in Main.
While checkForNotify
' Check for a notification of an approaching collection.
Dim s As GCNotificationStatus = GC.WaitForFullGCApproach
If (s = GCNotificationStatus.Succeeded) Then
Console.WriteLine("GC Notification raised.")
OnFullGCApproachNotify()
ElseIf (s = GCNotificationStatus.Canceled) Then
Console.WriteLine("GC Notification cancelled.")
Exit While
Else
' This can occur if a timeout period
' is specified for WaitForFullGCApproach(Timeout)
' or WaitForFullGCComplete(Timeout)
' and the time out period has elapsed.
Console.WriteLine("GC Notification not applicable.")
Exit While
End If
' Check for a notification of a completed collection.
s = GC.WaitForFullGCComplete
If (s = GCNotificationStatus.Succeeded) Then
Console.WriteLine("GC Notification raised.")
OnFullGCCompleteEndNotify()
ElseIf (s = GCNotificationStatus.Canceled) Then
Console.WriteLine("GC Notification cancelled.")
Exit While
Else
' Could be a time out.
Console.WriteLine("GC Notification not applicable.")
Exit While
End If
End While
Thread.Sleep(500)
' FinalExit is set to true right before
' the main thread cancelled notification.
If finalExit Then
Exit While
End If
End While
End Sub
下面的代码包含 OnFullGCApproachNotify 方法，调用自
WaitForFullGCProc 方法。
public:
static void OnFullGCApproachNotify()
{
Console::WriteLine("Redirecting requests.");
// Method that tells the request queuing
// server to not direct requests to this server.
RedirectRequests();
// Method that provides time to
// finish processing pending requests.
FinishExistingRequests();
// This is a good time to induce a GC collection
// because the runtime will induce a full GC soon.
// To be very careful, you can check precede with a
// check of the GC.GCCollectionCount to make sure
// a full GC did not already occur since last notified.
GC::Collect();
Console::WriteLine("Induced a collection.");
}
public static void OnFullGCApproachNotify()
{
Console.WriteLine("Redirecting requests.");
// Method that tells the request queuing
// server to not direct requests to this server.
RedirectRequests();
// Method that provides time to
// finish processing pending requests.
FinishExistingRequests();
// This is a good time to induce a GC collection
// because the runtime will induce a full GC soon.
// To be very careful, you can check precede with a
// check of the GC.GCCollectionCount to make sure
// a full GC did not already occur since last notified.
GC.Collect();
Console.WriteLine("Induced a collection.");
}
Public Shared Sub OnFullGCApproachNotify()
Console.WriteLine("Redirecting requests.")
' Method that tells the request queuing
' server to not direct requests to this server.
RedirectRequests()
' Method that provides time to
' finish processing pending requests.
FinishExistingRequests()
' This is a good time to induce a GC collection
' because the runtime will induce a ful GC soon.
' To be very careful, you can check precede with a
' check of the GC.GCCollectionCount to make sure
' a full GC did not already occur since last notified.
GC.Collect()
Console.WriteLine("Induced a collection.")
End Sub
下面的代码包含 OnFullGCApproachComplete 方法，调用自
WaitForFullGCProc 方法。
public:
static void OnFullGCCompleteEndNotify()
{
// Method that informs the request queuing server
// that this server is ready to accept requests again.
AcceptRequests();
Console::WriteLine("Accepting requests again.");
}
public static void OnFullGCCompleteEndNotify()
{
// Method that informs the request queuing server
// that this server is ready to accept requests again.
AcceptRequests();
Console.WriteLine("Accepting requests again.");
}
Public Shared Sub OnFullGCCompleteEndNotify()
' Method that informs the request queuing server
' that this server is ready to accept requests again.
AcceptRequests()
Console.WriteLine("Accepting requests again.")
End Sub
下面的代码包含调用自 OnFullGCApproachNotify 和 OnFullGCCompleteNotify 方法的用户方法。 用户方法重定向请求，完成现有请求，再在发生完全垃圾回收后继续执行请求。
private:
static void RedirectRequests()
{
// Code that sends requests
// to other servers.
// Suspend work.
bAllocate = false;
}
static void FinishExistingRequests()
{
// Code that waits a period of time
// for pending requests to finish.
// Clear the simulated workload.
load->Clear();
}
static void AcceptRequests()
{
// Code that resumes processing
// requests on this server.
// Resume work.
bAllocate = true;
}
private static void RedirectRequests()
{
// Code that sends requests
// to other servers.
// Suspend work.
bAllocate = false;
}
private static void FinishExistingRequests()
{
// Code that waits a period of time
// for pending requests to finish.
// Clear the simulated workload.
load.Clear();
}
private static void AcceptRequests()
{
// Code that resumes processing
// requests on this server.
// Resume work.
bAllocate = true;
}
Private Shared Sub RedirectRequests()
' Code that sends requests
' to other servers.
' Suspend work.
bAllocate = False
End Sub
Private Shared Sub FinishExistingRequests()
' Code that waits a period of time
' for pending requests to finish.
' Clear the simulated workload.
load.Clear()
End Sub
Private Shared Sub AcceptRequests()
' Code that resumes processing
' requests on this server.
' Resume work.
bAllocate = True
End Sub
整个代码示例如下所示：
using namespace System;
using namespace System::Collections::Generic;
using namespace System::Threading;
namespace GCNotify
{
ref class Program
{
private:
// Variable for continual checking in the
// While loop in the WaitForFullGCProc method.
static bool checkForNotify = false;
// Variable for suspending work
// (such servicing allocated server requests)
// after a notification is received and then
// resuming allocation after inducing a garbage collection.
static bool bAllocate = false;
// Variable for ending the example.
static bool finalExit = false;
// Collection for objects that
// simulate the server request workload.
static List<array<Byte>^>^ load = gcnew List<array<Byte>^>();
public:
static void Main()
{
try
{
// Register for a notification.
GC::RegisterForFullGCNotification(10, 10);
Console::WriteLine("Registered for GC notification.");
checkForNotify = true;
bAllocate = true;
// Start a thread using WaitForFullGCProc.
Thread^ thWaitForFullGC = gcnew Thread(gcnew ThreadStart(&WaitForFullGCProc));
thWaitForFullGC->Start();
// While the thread is checking for notifications in
// WaitForFullGCProc, create objects to simulate a server workload.
try
{
int lastCollCount = 0;
int newCollCount = 0;
while (true)
{
if (bAllocate)
{
load->Add(gcnew array<Byte>(1000));
newCollCount = GC::CollectionCount(2);
if (newCollCount != lastCollCount)
{
// Show collection count when it increases:
Console::WriteLine("Gen 2 collection count: {0}", GC::CollectionCount(2).ToString());
lastCollCount = newCollCount;
}
// For ending the example (arbitrary).
if (newCollCount == 500)
{
finalExit = true;
checkForNotify = false;
break;
}
}
}
}
catch (OutOfMemoryException^)
{
Console::WriteLine("Out of memory.");
}
finalExit = true;
checkForNotify = false;
GC::CancelFullGCNotification();
}
catch (InvalidOperationException^ invalidOp)
{
Console::WriteLine("GC Notifications are not supported while concurrent GC is enabled.\n"
+ invalidOp->Message);
}
}
public:
static void OnFullGCApproachNotify()
{
Console::WriteLine("Redirecting requests.");
// Method that tells the request queuing
// server to not direct requests to this server.
RedirectRequests();
// Method that provides time to
// finish processing pending requests.
FinishExistingRequests();
// This is a good time to induce a GC collection
// because the runtime will induce a full GC soon.
// To be very careful, you can check precede with a
// check of the GC.GCCollectionCount to make sure
// a full GC did not already occur since last notified.
GC::Collect();
Console::WriteLine("Induced a collection.");
}
public:
static void OnFullGCCompleteEndNotify()
{
// Method that informs the request queuing server
// that this server is ready to accept requests again.
AcceptRequests();
Console::WriteLine("Accepting requests again.");
}
public:
static void WaitForFullGCProc()
{
while (true)
{
// CheckForNotify is set to true and false in Main.
while (checkForNotify)
{
// Check for a notification of an approaching collection.
GCNotificationStatus s = GC::WaitForFullGCApproach();
if (s == GCNotificationStatus::Succeeded)
{
Console::WriteLine("GC Notification raised.");
OnFullGCApproachNotify();
}
else if (s == GCNotificationStatus::Canceled)
{
Console::WriteLine("GC Notification cancelled.");
break;
}
else
{
// This can occur if a timeout period
// is specified for WaitForFullGCApproach(Timeout)
// or WaitForFullGCComplete(Timeout)
// and the time out period has elapsed.
Console::WriteLine("GC Notification not applicable.");
break;
}
// Check for a notification of a completed collection.
s = GC::WaitForFullGCComplete();
if (s == GCNotificationStatus::Succeeded)
{
Console::WriteLine("GC Notification raised.");
OnFullGCCompleteEndNotify();
}
else if (s == GCNotificationStatus::Canceled)
{
Console::WriteLine("GC Notification cancelled.");
break;
}
else
{
// Could be a time out.
Console::WriteLine("GC Notification not applicable.");
break;
}
}
Thread::Sleep(500);
// FinalExit is set to true right before
// the main thread cancelled notification.
if (finalExit)
{
break;
}
}
}
private:
static void RedirectRequests()
{
// Code that sends requests
// to other servers.
// Suspend work.
bAllocate = false;
}
static void FinishExistingRequests()
{
// Code that waits a period of time
// for pending requests to finish.
// Clear the simulated workload.
load->Clear();
}
static void AcceptRequests()
{
// Code that resumes processing
// requests on this server.
// Resume work.
bAllocate = true;
}
};
}
int main()
{
GCNotify::Program::Main();
}
using System;
using System.Collections.Generic;
using System.Threading;
namespace GCNotify
{
class Program
{
// Variable for continual checking in the
// While loop in the WaitForFullGCProc method.
static bool checkForNotify = false;
// Variable for suspending work
// (such servicing allocated server requests)
// after a notification is received and then
// resuming allocation after inducing a garbage collection.
static bool bAllocate = false;
// Variable for ending the example.
static bool finalExit = false;
// Collection for objects that
// simulate the server request workload.
static List<byte[]> load = new List<byte[]>();
public static void Main(string[] args)
{
try
{
// Register for a notification.
GC.RegisterForFullGCNotification(10, 10);
Console.WriteLine("Registered for GC notification.");
checkForNotify = true;
bAllocate = true;
// Start a thread using WaitForFullGCProc.
Thread thWaitForFullGC = new Thread(new ThreadStart(WaitForFullGCProc));
thWaitForFullGC.Start();
// While the thread is checking for notifications in
// WaitForFullGCProc, create objects to simulate a server workload.
try
{
int lastCollCount = 0;
int newCollCount = 0;
while (true)
{
if (bAllocate)
{
load.Add(new byte[1000]);
newCollCount = GC.CollectionCount(2);
if (newCollCount != lastCollCount)
{
// Show collection count when it increases:
Console.WriteLine("Gen 2 collection count: {0}", GC.CollectionCount(2).ToString());
lastCollCount = newCollCount;
}
// For ending the example (arbitrary).
if (newCollCount == 500)
{
finalExit = true;
checkForNotify = false;
break;
}
}
}
}
catch (OutOfMemoryException)
{
Console.WriteLine("Out of memory.");
}
finalExit = true;
checkForNotify = false;
GC.CancelFullGCNotification();
}
catch (InvalidOperationException invalidOp)
{
Console.WriteLine("GC Notifications are not supported while concurrent GC is enabled.\n"
+ invalidOp.Message);
}
}
public static void OnFullGCApproachNotify()
{
Console.WriteLine("Redirecting requests.");
// Method that tells the request queuing
// server to not direct requests to this server.
RedirectRequests();
// Method that provides time to
// finish processing pending requests.
FinishExistingRequests();
// This is a good time to induce a GC collection
// because the runtime will induce a full GC soon.
// To be very careful, you can check precede with a
// check of the GC.GCCollectionCount to make sure
// a full GC did not already occur since last notified.
GC.Collect();
Console.WriteLine("Induced a collection.");
}
public static void OnFullGCCompleteEndNotify()
{
// Method that informs the request queuing server
// that this server is ready to accept requests again.
AcceptRequests();
Console.WriteLine("Accepting requests again.");
}
public static void WaitForFullGCProc()
{
while (true)
{
// CheckForNotify is set to true and false in Main.
while (checkForNotify)
{
// Check for a notification of an approaching collection.
GCNotificationStatus s = GC.WaitForFullGCApproach();
if (s == GCNotificationStatus.Succeeded)
{
Console.WriteLine("GC Notification raised.");
OnFullGCApproachNotify();
}
else if (s == GCNotificationStatus.Canceled)
{
Console.WriteLine("GC Notification cancelled.");
break;
}
else
{
// This can occur if a timeout period
// is specified for WaitForFullGCApproach(Timeout)
// or WaitForFullGCComplete(Timeout)
// and the time out period has elapsed.
Console.WriteLine("GC Notification not applicable.");
break;
}
// Check for a notification of a completed collection.
GCNotificationStatus status = GC.WaitForFullGCComplete();
if (status == GCNotificationStatus.Succeeded)
{
Console.WriteLine("GC Notification raised.");
OnFullGCCompleteEndNotify();
}
else if (status == GCNotificationStatus.Canceled)
{
Console.WriteLine("GC Notification cancelled.");
break;
}
else
{
// Could be a time out.
Console.WriteLine("GC Notification not applicable.");
break;
}
}
Thread.Sleep(500);
// FinalExit is set to true right before
// the main thread cancelled notification.
if (finalExit)
{
break;
}
}
}
private static void RedirectRequests()
{
// Code that sends requests
// to other servers.
// Suspend work.
bAllocate = false;
}
private static void FinishExistingRequests()
{
// Code that waits a period of time
// for pending requests to finish.
// Clear the simulated workload.
load.Clear();
}
private static void AcceptRequests()
{
// Code that resumes processing
// requests on this server.
// Resume work.
bAllocate = true;
}
}
}
Imports System.Collections.Generic
Imports System.Threading
Class Program
' Variables for continual checking in the
' While loop in the WaitForFullGcProc method.
Private Shared checkForNotify As Boolean = False
' Variable for suspending work
' (such as servicing allocated server requests)
' after a notification is received and then
' resuming allocation after inducing a garbage collection.
Private Shared bAllocate As Boolean = False
' Variable for ending the example.
Private Shared finalExit As Boolean = False
' Collection for objects that
' simulate the server request workload.
Private Shared load As New List(Of Byte())
Public Shared Sub Main(ByVal args() As String)
Try
' Register for a notification.
GC.RegisterForFullGCNotification(10, 10)
Console.WriteLine("Registered for GC notification.")
bAllocate = True
checkForNotify = True
' Start a thread using WaitForFullGCProc.
Dim thWaitForFullGC As Thread = _
New Thread(New ThreadStart(AddressOf WaitForFullGCProc))
thWaitForFullGC.Start()
' While the thread is checking for notifications in
' WaitForFullGCProc, create objects to simulate a server workload.
Try
Dim lastCollCount As Integer = 0
Dim newCollCount As Integer = 0
While (True)
If bAllocate = True Then
load.Add(New Byte(1000) {})
newCollCount = GC.CollectionCount(2)
If (newCollCount <> lastCollCount) Then
' Show collection count when it increases:
Console.WriteLine("Gen 2 collection count: {0}", _
GC.CollectionCount(2).ToString)
lastCollCount = newCollCount
End If
' For ending the example (arbitrary).
If newCollCount = 500 Then
finalExit = True
checkForNotify = False
bAllocate = False
Exit While
End If
End If
End While
Catch outofMem As OutOfMemoryException
Console.WriteLine("Out of memory.")
End Try
finalExit = True
checkForNotify = False
GC.CancelFullGCNotification()
Catch invalidOp As InvalidOperationException
Console.WriteLine("GC Notifications are not supported while concurrent GC is enabled." _
& vbLf & invalidOp.Message)
End Try
End Sub
Public Shared Sub OnFullGCApproachNotify()
Console.WriteLine("Redirecting requests.")
' Method that tells the request queuing
' server to not direct requests to this server.
RedirectRequests()
' Method that provides time to
' finish processing pending requests.
FinishExistingRequests()
' This is a good time to induce a GC collection
' because the runtime will induce a ful GC soon.
' To be very careful, you can check precede with a
' check of the GC.GCCollectionCount to make sure
' a full GC did not already occur since last notified.
GC.Collect()
Console.WriteLine("Induced a collection.")
End Sub
Public Shared Sub OnFullGCCompleteEndNotify()
' Method that informs the request queuing server
' that this server is ready to accept requests again.
AcceptRequests()
Console.WriteLine("Accepting requests again.")
End Sub
Public Shared Sub WaitForFullGCProc()
While True
' CheckForNotify is set to true and false in Main.
While checkForNotify
' Check for a notification of an approaching collection.
Dim s As GCNotificationStatus = GC.WaitForFullGCApproach
If (s = GCNotificationStatus.Succeeded) Then
Console.WriteLine("GC Notification raised.")
OnFullGCApproachNotify()
ElseIf (s = GCNotificationStatus.Canceled) Then
Console.WriteLine("GC Notification cancelled.")
Exit While
Else
' This can occur if a timeout period
' is specified for WaitForFullGCApproach(Timeout)
' or WaitForFullGCComplete(Timeout)
' and the time out period has elapsed.
Console.WriteLine("GC Notification not applicable.")
Exit While
End If
' Check for a notification of a completed collection.
s = GC.WaitForFullGCComplete
If (s = GCNotificationStatus.Succeeded) Then
Console.WriteLine("GC Notification raised.")
OnFullGCCompleteEndNotify()
ElseIf (s = GCNotificationStatus.Canceled) Then
Console.WriteLine("GC Notification cancelled.")
Exit While
Else
' Could be a time out.
Console.WriteLine("GC Notification not applicable.")
Exit While
End If
End While
Thread.Sleep(500)
' FinalExit is set to true right before
' the main thread cancelled notification.
If finalExit Then
Exit While
End If
End While
End Sub
Private Shared Sub RedirectRequests()
' Code that sends requests
' to other servers.
' Suspend work.
bAllocate = False
End Sub
Private Shared Sub FinishExistingRequests()
' Code that waits a period of time
' for pending requests to finish.
' Clear the simulated workload.
load.Clear()
End Sub
Private Shared Sub AcceptRequests()
' Code that resumes processing
' requests on this server.
' Resume work.
bAllocate = True
End Sub
End Class
请参阅
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