GC.KeepAlive メソッド
指定したオブジェクトを参照し、現在のルーチンの開始時からこのメソッドが呼び出される時点までの間、そのオブジェクトをガベージ コレクションの対象から外します。 名前空間: System
アセンブリ: mscorlib (mscorlib.dll 内)
構文
解説
使用例
プラットフォーム
バージョン情報
参照
アセンブリ: mscorlib (mscorlib.dll 内)
構文解説KeepAlive メソッドの目的は、ガベージ コレクタにより時期尚早に収集されるおそれがあるオブジェクトが確実に参照されるようにすることです。このような危険が起こり得るのは、マネージ コードまたはマネージ データではオブジェクトが参照されていないが、そのオブジェクトが、Win32 API、アンマネージ DLL、COM を使用するメソッドなどのアンマネージ コードで依然として使用されている場合です。
メソッド内でオブジェクトが作成されて使用される場合も、ガベージ コレクションが不完全になります。最初のコード例のように、オブジェクトのいずれかのメンバに対する呼び出しを実行している間に、オブジェクトが再要求される場合があります。
このメソッドは、obj オブジェクトを参照し、ルーチンの開始時からこのメソッドが呼び出される時点までの間、そのオブジェクトをガベージ コレクションの対象から外します。このメソッドのコードは、obj を使用可能にする必要がある命令の範囲の最初ではなく最後に作成します。
KeepAlive メソッドでは何も実行されず、パラメータとして渡されるオブジェクトの有効期間が延長される以外に副作用は発生しません。
使用例このセクションには、2 つのコード例が含まれています。最初の例は、KeepAlive メソッドを使用して積極的なガベージ コレクションを防ぐ方法を示しています。2 番目の例は、長時間実行されるメソッドで KeepAlive を使用する方法を示しています。
収集したオブジェクトのメソッドの実行中に積極的なガベージ コレクションの発生を KeepAlive メソッドによって防止するコード例を次に示します。
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この例では、テスト メソッドを繰り返し呼び出すスレッドを起動します。このスレッドは、Enter キーを押すまで、実行されます。既定では、このコード例では、DoWork メソッドが実行され、その結果、Example オブジェクトが作成されて、Hash プロパティが読み取られます。DoWork メソッドでは KeepAlive メソッドを使用しないので、Example オブジェクトのプロパティが読み取られる前に、そのオブジェクトのファイナライザが実行されることがあります。DoWork メソッドでは、この処理が検出され、コンソール メッセージが表示されます。
引数 KeepAlive を指定してこの例を実行すると、SafeDoWork メソッドが実行されます。SafeDoWork メソッドは、KeepAlive メソッドを呼び出す最後の行を除いて DoWork メソッドと同じです。この行によって、SafeDoWork メソッドの処理が完了するまで、Example オブジェクトが再要求されません。
引数 Trivial を指定してこの例を実行すると、Trivial メソッドが実行されます。このメソッドは、Hash プロパティより高速な整数プロパティにアクセスします。このプロパティへのアクセス速度は速いため、ファイナライザが先に実行されることはほとんどありません。
Imports System Imports System.Threading Public Class Example ' The N property is very fast, because all it does is return ' a stored integer. Therefore the finalizer almost never runs ' before this property is read. ' Private nValue As Integer Public ReadOnly Property N() As Integer Get Return nValue End Get End Property ' The Hash property is slower because it clones an array. When ' KeepAlive is not used, the finalizer sometimes runs before ' the Hash property value is read. ' Private hashValue() As Byte Public ReadOnly Property Hash() As Byte() Get Return CType(hashValue.Clone(), Byte()) End Get End Property ' The constructor initializes the property values. ' Public Sub New() nValue = 2 hashValue = New Byte(19) {} hashValue(0) = 2 End Sub ' The finalizer sets the N property to zero, and clears all ' the elements of the array for the Hash property. The finalizer ' runs on a separate thread provided by the system. In some ' cases, the finalizer can run while a member of the Example ' instance is still executing. ' Overloads Protected Overrides Sub Finalize() nValue = 0 If Not (hashValue Is Nothing) Then Array.Clear(hashValue, 0, hashValue.Length) End If MyBase.Finalize() End Sub End Class Public Class Test Private Shared totalCount As Integer = 0 Private Shared finalizerFirstCount As Integer = 0 ' This variable controls the thread that runs the demo. Private Shared running As Boolean = True ' The default is to run without KeepAlive. Private Shared kind As TestKind = TestKind.NoKeepAlive ' See the comment at the end of the SafeDoWork method. 'private static bool keepAlive = false; ' In order to demonstrate the finalizer running first, the ' DoWork method must create an Example object and invoke its ' Hash property. If there are no other calls to members of ' the Example object in DoWork, garbage collection reclaims ' the Example object aggressively. Sometimes this means that ' the finalizer runs before the call to the Hash property ' completes. Private Shared Sub DoWork() ' Count the number of times DoWork executes. totalCount += 1 ' Create an Example object and save the value of the ' Hash property. There are no more calls to members of ' the object in the DoWork method, so it is available ' for aggressive garbage collection. ' Dim ex As New Example() Dim res As Byte() = ex.Hash ' If the finalizer runs before the call to the Hash ' property completes, the hashValue array might be ' cleared before the property value is read. The ' following test detects that. ' If res(0) <> 2 Then finalizerFirstCount += 1 Console.WriteLine("The finalizer ran first at {0} iterations.", _ totalCount) End If End Sub ' In the SafeDoWork method the finalizer never runs first, ' because of the KeepAlive at the end of the method. ' Private Shared Sub SafeDoWork() totalCount += 1 ' Create an Example object and save the value of the ' Hash property. Dim ex As New Example() Dim res As Byte() = ex.Hash ' The finalizer cannot run before the property is read, ' because the KeepAlive method prevents the Example object ' from being reclaimed by garbage collection. ' If res(0) <> 2 Then finalizerFirstCount += 1 Console.WriteLine("The finalizer ran first at {0} iterations.", _ totalCount) End If GC.KeepAlive(ex) ' The KeepAlive method need never be executed. For example, ' if the keepAlive field is uncommented, the following line ' of code prevents the finalizer from running first, even ' though it is impossible for the KeepAlive method ever to ' be executed. ' if (keepAlive) GC.KeepAlive(ex); ' However, if the compiler detects that the KeepAlive can ' never be executed, as in the following line, then it will ' not prevent the finalizer from running first. ' if (false) GC.KeepAlive(ex); End Sub ' In the TrivialDoWork method the finalizer almost never runs ' first, even without a KeepAlive at the end of the method, ' because accessing the N property is so fast. ' Private Shared Sub TrivialDoWork() totalCount += 1 ' Create an Example object and save the value of the ' N property. Dim ex As New Example() Dim res As Integer = ex.N ' The finalizer almost never runs before the property is read , ' because accessing the N property is so fast. ' If res <> 2 Then finalizerFirstCount += 1 Console.WriteLine("The finalizer ran first at {0} iterations.", _ totalCount) End If End Sub Public Shared Sub Main(ByVal args() As String) ' Check to see what command-line argument was passed. If args.Length <> 0 Then Dim arg As String = args(0).ToLower() ' The AndAlso operator prevents the second condition from ' being evaluated if the first condition is false. If (arg.Length < 10) AndAlso _ (arg = "keepalive".Substring(0, arg.Length)) Then kind = TestKind.KeepAlive End If If arg.Length < 8 AndAlso _ arg = "trivial".Substring(0, arg.Length) Then kind = TestKind.Trivial End If End If Console.WriteLine("Test: {0}", kind) ' Create a thread to run the test. Dim t As New Thread(New ThreadStart(AddressOf ThreadProc)) t.Start() ' The thread runs until Enter is pressed. Console.WriteLine("Press Enter to stop the program.") Console.ReadLine() running = False ' Wait for the thread to end. t.Join() Console.WriteLine("{0} iterations total; the " & _ "finalizer ran first {1} times.", _ totalCount, finalizerFirstCount) End Sub ' This method executes the selected test. Private Shared Sub ThreadProc() Select Case kind Case TestKind.KeepAlive While running SafeDoWork() End While Case TestKind.Trivial While running TrivialDoWork() End While Case Else While running DoWork() End While End Select End Sub Private Enum TestKind NoKeepAlive KeepAlive Trivial End Enum End Class ' When run with the default NoKeepAlive test, on a dual-processor ' computer, this example produces output similar to the following: ' 'Test: NoKeepAlive 'Press Enter to stop the program. 'The finalizer ran first at 21098618 iterations. 'The finalizer ran first at 33944444 iterations. 'The finalizer ran first at 35160207 iterations. ' '53169451 iterations total; the finalizer ran first 3 times. '
using System; using System.Threading; public class Example { // The N property is very fast, because all it does is return // a stored integer. Therefore the finalizer almost never runs // before this property is read. // private int nValue; public int N { get { return nValue; }} // The Hash property is slower because it clones an array. When // KeepAlive is not used, the finalizer sometimes runs before // the Hash property value is read. // private byte[] hashValue; public byte[] Hash { get { return (byte[]) hashValue.Clone(); }} // The constructor initializes the property values. // public Example() { nValue = 2; hashValue = new byte[20]; hashValue[0] = 2; } // The finalizer sets the N property to zero, and clears all // the elements of the array for the Hash property. The finalizer // runs on a separate thread provided by the system. In some // cases, the finalizer can run while a member of the Example // instance is still executing. // ~Example() { nValue = 0; if (hashValue != null) { Array.Clear(hashValue, 0, hashValue.Length); } } } public class Test { private static int totalCount = 0; private static int finalizerFirstCount = 0; // This variable controls the thread that runs the demo. private static bool running = true; // The default is to run without KeepAlive. private static TestKind kind = TestKind.NoKeepAlive; // See the comment at the end of the SafeDoWork method. //private static bool keepAlive = false; // In order to demonstrate the finalizer running first, the // DoWork method must create an Example object and invoke its // Hash property. If there are no other calls to members of // the Example object in DoWork, garbage collection reclaims // the Example object aggressively. Sometimes this means that // the finalizer runs before the call to the Hash property // completes. private static void DoWork() { totalCount++; // Create an Example object and save the value of the // Hash property. There are no more calls to members of // the object in the DoWork method, so it is available // for aggressive garbage collection. // Example ex = new Example(); byte[] res = ex.Hash; // If the finalizer runs before the call to the Hash // property completes, the hashValue array might be // cleared before the property value is read. The // following test detects that. // if (res[0] != 2) { finalizerFirstCount++; Console.WriteLine("The finalizer ran first at {0} iterations." , totalCount); } } // In the SafeDoWork method the finalizer never runs first, // because of the KeepAlive at the end of the method. // private static void SafeDoWork() { totalCount++; // Create an Example object and save the value of the // Hash property. Example ex = new Example(); byte[] res = ex.Hash; // The finalizer cannot run before the property is read, // because the KeepAlive method prevents the Example object // from being reclaimed by garbage collection. // if (res[0] != 2) { finalizerFirstCount++; Console.WriteLine("The finalizer ran first at {0} iterations." , totalCount); } GC.KeepAlive(ex); // The KeepAlive method need never be executed. For example , // if the keepAlive field is uncommented, the following line // of code prevents the finalizer from running first, even // though it is impossible for the KeepAlive method ever to // be executed. // if (keepAlive) GC.KeepAlive(ex); // However, if the compiler detects that the KeepAlive can // never be executed, as in the following line, then it will // not prevent the finalizer from running first. // if (false) GC.KeepAlive(ex); } // In the TrivialDoWork method the finalizer almost never runs // first, even without a KeepAlive at the end of the method, // because accessing the N property is so fast. // private static void TrivialDoWork() { totalCount++; // Create an Example object and save the value of the // N property. Example ex = new Example(); int res = ex.N; // The finalizer almost never runs before the property is read , // because accessing the N property is so fast. // if (res != 2) { finalizerFirstCount++; Console.WriteLine("The finalizer ran first at {0} iterations." , totalCount); } } public static void Main (string[] args) { if (args.Length != 0) { string arg = args[0].ToLower(); if (arg.Length < 10 && arg == "keepalive".Substring(0, arg.Length)) kind = TestKind.KeepAlive; if (arg.Length < 8 && arg == "trivial".Substring(0, arg.Length)) kind = TestKind.Trivial; } Console.WriteLine("Test: {0}", kind); // Create a thread to run the test. Thread t = new Thread(new ThreadStart(ThreadProc)); t.Start(); // The thread runs until Enter is pressed. Console.WriteLine("Press Enter to stop the program."); Console.ReadLine(); running = false; // Wait for the thread to end. t.Join(); Console.WriteLine("{0} iterations total; the finalizer ran first {1} times.", totalCount, finalizerFirstCount); } private static void ThreadProc() { switch (kind) { case TestKind.KeepAlive: while (running) SafeDoWork(); break; case TestKind.Trivial: while (running) TrivialDoWork(); break; default: while (running) DoWork(); break; } } private enum TestKind { NoKeepAlive, KeepAlive, Trivial } } /* When run with the default NoKeepAlive test, on a dual-processor computer, this example produces output similar to the following: Test: NoKeepAlive Press Enter to stop the program. The finalizer ran first at 21098618 iterations. The finalizer ran first at 33944444 iterations. The finalizer ran first at 35160207 iterations. 53169451 iterations total; the finalizer ran first 3 times. */
using namespace System; using namespace System::Threading; public ref class Example { // The N property is very fast, because all it does is return // a stored integer. Therefore the finalizer almost never runs // before this property is read. // private: int nValue; public: property int N { int get() { return nValue; } } // The Hash property is slower because it clones an array. When // KeepAlive is not used, the finalizer sometimes runs before // the Hash property value is read. // private: array<Byte>^ hashValue; public: property array<Byte>^ Hash { array<Byte>^ get() { return (array<Byte>^) hashValue->Clone(); } } // The constructor initializes the property values. // public: Example() { nValue = 2; hashValue = gcnew array<Byte>(20); hashValue[0] = 2; } // The finalizer sets the N property to zero, and clears all // the elements of the array for the Hash property. The finalizer // runs on a separate thread provided by the system. In some // cases, the finalizer can run while a member of the Example // instance is still executing. // ~Example() { nValue = 0; if (hashValue != nullptr) { Array::Clear(hashValue, 0, hashValue->Length); } } }; public ref class Test { private: enum class TestKind { NoKeepAlive, KeepAlive, Trivial }; private: static int totalCount; private: static int finalizerFirstCount; // This variable controls the thread that runs the demo. private: static bool running = true; // The default is to run without KeepAlive. private: static TestKind kind = TestKind::NoKeepAlive; // See the comment at the end of the SafeDoWork method. //private static bool keepAlive = false; // In order to demonstrate the finalizer running first, the // DoWork method must create an Example object and invoke its // Hash property. If there are no other calls to members of // the Example object in DoWork, garbage collection reclaims // the Example object aggressively. Sometimes this means that // the finalizer runs before the call to the Hash property // completes. private: static void DoWork() { totalCount++; // Create an Example object and save the value of the // Hash property. There are no more calls to members of // the object in the DoWork method, so it is available // for aggressive garbage collection. // Example^ exampleObject = gcnew Example(); array<Byte>^ hashArray = exampleObject->Hash; // If the finalizer runs before the call to the Hash // property completes, the hashValue array might be // cleared before the property value is read. The // following test detects that. // if (hashArray[0] != 2) { finalizerFirstCount++; Console::WriteLine("The finalizer ran first at {0}"+ "iterations.",totalCount); } } // In the SafeDoWork method the finalizer never runs first, // because of the KeepAlive at the end of the method. // private: static void SafeDoWork() { totalCount++; // Create an Example object and save the value of the // Hash property. Example^ exampleObject = gcnew Example(); array<Byte>^ hashArray = exampleObject->Hash; // The finalizer cannot run before the property is read, // because the KeepAlive method prevents the Example object // from being reclaimed by garbage collection. // if (hashArray[0] != 2) { finalizerFirstCount++; Console::WriteLine("The finalizer ran first at {0}"+ "iterations.",totalCount); } GC::KeepAlive(exampleObject); // The KeepAlive method need never be executed. For example , // if the keepAlive field is uncommented, the following line // of code prevents the finalizer from running first, even // though it is impossible for the KeepAlive method ever to // be executed. // if (keepAlive) GC.KeepAlive(ex); // However, if the compiler detects that the KeepAlive can // never be executed, as in the following line, then it will // not prevent the finalizer from running first. // if (false) GC.KeepAlive(ex); } // In the TrivialDoWork method the finalizer almost never runs // first, even without a KeepAlive at the end of the method, // because accessing the N property is so fast. // private: static void TrivialDoWork() { totalCount++; // Create an Example object and save the value of the // N property. Example^ exampleObject = gcnew Example(); int hashArray = exampleObject->N; // The finalizer almost never runs before the property is // read because accessing the N property is so fast. // if (hashArray != 2) { finalizerFirstCount++; Console::WriteLine("The finalizer ran first at {0}"+ "iterations.",totalCount); } } public: static void Work(array<String^>^ args) { if (args->Length != 0) { String^ arg = args[0]->ToLower(); if (arg == "keepalive") { kind = TestKind::KeepAlive; } if (arg == "trivial") { kind = TestKind::Trivial; } } Console::WriteLine("Test: {0}", kind); // Create a thread to run the test. Thread^ sampleThread = gcnew Thread( gcnew ThreadStart(ThreadProc)); sampleThread->Start(); // The thread runs until Enter is pressed. Console::WriteLine("Press Enter to stop the program."); Console::ReadLine(); running = false; // Wait for the thread to end. sampleThread->Join(); Console::WriteLine("{0} iterations total; the finalizer ran " + "first {1} times.",totalCount, finalizerFirstCount); } private: static void ThreadProc() { switch (kind) { case TestKind::KeepAlive: while(running) { SafeDoWork(); } break; case TestKind::Trivial: while(running) { TrivialDoWork(); } break; default: while(running) { DoWork(); } break; } } }; int main(array<String^>^ args) { Test::Work(args); }; /* When run with the default NoKeepAlive test, on a dual-processor computer, this example produces output similar to the following: Test: NoKeepAlive Press Enter to stop the program. The finalizer ran first at 21098618 iterations. The finalizer ran first at 33944444 iterations. The finalizer ran first at 35160207 iterations. 53169451 iterations total; the finalizer ran first 3 times. */
オブジェクトの Main メソッドの冒頭でオブジェクトを作成し、最後に KeepAlive メソッドを呼び出すまでそのオブジェクトを参照しないコード例を次に示します。Collect メソッドおよび WaitForPendingFinalizers メソッドを呼び出しても、このオブジェクトは、30 秒間持続する Main メソッドの実行中は存在します。
Imports System Imports System.Threading Imports System.Runtime.InteropServices ' A simple class that exposes two static Win32 functions. ' One is a delegate type and the other is an enumerated type. Public Class MyWin32 ' Declare the SetConsoleCtrlHandler function as external ' and receiving a delegate. <DllImport("Kernel32")> _ Public Shared Function SetConsoleCtrlHandler(ByVal Handler As HandlerRoutine, _ ByVal Add As Boolean) As Boolean End Function ' A delegate type to be used as the handler routine ' for SetConsoleCtrlHandler. Delegate Function HandlerRoutine(ByVal CtrlType As CtrlTypes) As [Boolean] ' An enumerated type for the control messages ' sent to the handler routine. Public Enum CtrlTypes CTRL_C_EVENT = 0 CTRL_BREAK_EVENT CTRL_CLOSE_EVENT CTRL_LOGOFF_EVENT = 5 CTRL_SHUTDOWN_EVENT End Enum End Class Public Class MyApp ' A private static handler function in the MyApp class. Shared Function Handler(ByVal CtrlType As MyWin32.CtrlTypes) As [Boolean] Dim message As [String] = "This message should never be seen!" ' A select case to handle the event type. Select Case CtrlType Case MyWin32.CtrlTypes.CTRL_C_EVENT message = "A CTRL_C_EVENT was raised by the user." Case MyWin32.CtrlTypes.CTRL_BREAK_EVENT message = "A CTRL_BREAK_EVENT was raised by the user." Case MyWin32.CtrlTypes.CTRL_CLOSE_EVENT message = "A CTRL_CLOSE_EVENT was raised by the user." Case MyWin32.CtrlTypes.CTRL_LOGOFF_EVENT message = "A CTRL_LOGOFF_EVENT was raised by the user." Case MyWin32.CtrlTypes.CTRL_SHUTDOWN_EVENT message = "A CTRL_SHUTDOWN_EVENT was raised by the user." End Select ' Use interop to display a message for the type of event. Console.WriteLine(message) Return True End Function Public Shared Sub Main() ' Use interop to set a console control handler. Dim hr As New MyWin32.HandlerRoutine(AddressOf Handler) MyWin32.SetConsoleCtrlHandler(hr, True) ' Give the user some time to raise a few events. Console.WriteLine("Waiting 30 seconds for console ctrl events...") ' The object hr is not referred to again. ' The garbage collector can detect that the object has no ' more managed references and might clean it up here while ' the unmanaged SetConsoleCtrlHandler method is still using it. ' Force a garbage collection to demonstrate how the hr ' object will be handled. GC.Collect() GC.WaitForPendingFinalizers() GC.Collect() Thread.Sleep(30000) ' Display a message to the console when the unmanaged method ' has finished its work. Console.WriteLine("Finished!") ' Call GC.KeepAlive(hr) at this point to maintain a reference to hr. ' This will prevent the garbage collector from collecting the ' object during the execution of the SetConsoleCtrlHandler method. GC.KeepAlive(hr) Console.Read() End Sub End Class
using System; using System.Threading; using System.Runtime.InteropServices; // A simple class that exposes two static Win32 functions. // One is a delegate type and the other is an enumerated type. public class MyWin32 { // Declare the SetConsoleCtrlHandler function // as external and receiving a delegate. [DllImport("Kernel32")] public static extern Boolean SetConsoleCtrlHandler(HandlerRoutine Handler, Boolean Add); // A delegate type to be used as the handler routine // for SetConsoleCtrlHandler. public delegate Boolean HandlerRoutine(CtrlTypes CtrlType); // An enumerated type for the control messages // sent to the handler routine. public enum CtrlTypes { CTRL_C_EVENT = 0, CTRL_BREAK_EVENT, CTRL_CLOSE_EVENT, CTRL_LOGOFF_EVENT = 5, CTRL_SHUTDOWN_EVENT } } public class MyApp { // A private static handler function in the MyApp class. static Boolean Handler(MyWin32.CtrlTypes CtrlType) { String message = "This message should never be seen!"; // A switch to handle the event type. switch(CtrlType) { case MyWin32.CtrlTypes.CTRL_C_EVENT: message = "A CTRL_C_EVENT was raised by the user."; break; case MyWin32.CtrlTypes.CTRL_BREAK_EVENT: message = "A CTRL_BREAK_EVENT was raised by the user."; break; case MyWin32.CtrlTypes.CTRL_CLOSE_EVENT: message = "A CTRL_CLOSE_EVENT was raised by the user."; break; case MyWin32.CtrlTypes.CTRL_LOGOFF_EVENT: message = "A CTRL_LOGOFF_EVENT was raised by the user."; break; case MyWin32.CtrlTypes.CTRL_SHUTDOWN_EVENT: message = "A CTRL_SHUTDOWN_EVENT was raised by the user."; break; } // Use interop to display a message for the type of event. Console.WriteLine(message); return true; } public static void Main() { // Use interop to set a console control handler. MyWin32.HandlerRoutine hr = new MyWin32.HandlerRoutine(Handler); MyWin32.SetConsoleCtrlHandler(hr, true); // Give the user some time to raise a few events. Console.WriteLine("Waiting 30 seconds for console ctrl events..."); // The object hr is not referred to again. // The garbage collector can detect that the object has no // more managed references and might clean it up here while // the unmanaged SetConsoleCtrlHandler method is still using it. // Force a garbage collection to demonstrate how the hr // object will be handled. GC.Collect(); GC.WaitForPendingFinalizers(); GC.Collect(); Thread.Sleep(30000); // Display a message to the console when the unmanaged method // has finished its work. Console.WriteLine("Finished!"); // Call GC.KeepAlive(hr) at this point to maintain a reference to hr. // This will prevent the garbage collector from collecting the // object during the execution of the SetConsoleCtrlHandler method. GC.KeepAlive(hr); Console.Read(); } }
using namespace System; using namespace System::Threading; using namespace System::Runtime::InteropServices; // A simple class that exposes two static Win32 functions. // One is a delegate type and the other is an enumerated type. public ref class MyWin32 { public: // An enumerated type for the control messages sent to the handler routine. enum class CtrlTypes { CTRL_C_EVENT = 0, CTRL_BREAK_EVENT, CTRL_CLOSE_EVENT, CTRL_LOGOFF_EVENT = 5, CTRL_SHUTDOWN_EVENT }; delegate Boolean HandlerRoutine( // A delegate type to be used as the Handler Routine for SetConsoleCtrlHandler. CtrlTypes CtrlType ); // Declare the SetConsoleCtrlHandler function as external and receiving a delegate. [DllImport("Kernel32")] static Boolean SetConsoleCtrlHandler( HandlerRoutine^ Handler, Boolean Add ); }; public ref class MyApp { private: // A private static handler function in the MyApp class. static Boolean Handler( MyWin32::CtrlTypes CtrlType ) { String^ message = "This message should never be seen!"; // A switch to handle the event type. switch ( CtrlType ) { case MyWin32::CtrlTypes::CTRL_C_EVENT: message = "A CTRL_C_EVENT was raised by the user."; break; case MyWin32::CtrlTypes::CTRL_BREAK_EVENT: message = "A CTRL_BREAK_EVENT was raised by the user."; break; case MyWin32::CtrlTypes::CTRL_CLOSE_EVENT: message = "A CTRL_CLOSE_EVENT was raised by the user."; break; case MyWin32::CtrlTypes::CTRL_LOGOFF_EVENT: message = "A CTRL_LOGOFF_EVENT was raised by the user."; break; case MyWin32::CtrlTypes::CTRL_SHUTDOWN_EVENT: message = "A CTRL_SHUTDOWN_EVENT was raised by the user."; break; } // Use interop to display a message for the type of event. Console::WriteLine( message ); return true; } public: static void Test() { // Use interop to set a console control handler. MyWin32::HandlerRoutine^ hr = gcnew MyWin32::HandlerRoutine( Handler ); MyWin32::SetConsoleCtrlHandler( hr, true ); // Give the user some time to raise a few events. Console::WriteLine( "Waiting 30 seconds for console ctrl events..." ); // The Object hr is not referred to again. // The garbage collector can detect that the object has no // more managed references and might clean it up here while // the unmanaged SetConsoleCtrlHandler method is still using it. // Force a garbage collection to demonstrate how the hr // object will be handled. GC::Collect(); GC::WaitForPendingFinalizers(); GC::Collect(); Thread::Sleep( 30000 ); // Display a message to the console when the unmanaged method // has finished its work. Console::WriteLine( "Finished!" ); // Call GC::KeepAlive(hr) at this point to maintain a reference to hr. // This will prevent the garbage collector from collecting the // object during the execution of the SetConsoleCtrlHandler method. GC::KeepAlive( hr ); } }; int main() { MyApp::Test(); }
import System.* ; import System.Threading.* ; import System.Runtime.InteropServices.* ; // A simple class that exposes two static Win32 functions. // One is a delegate type and the other is an enumerated type. public class MyWin32 { // Declare the SetConsoleCtrlHandler function // as external and receiving a delegate. /** @attribute DllImport("Kernel32") */ public static native boolean SetConsoleCtrlHandler(HandlerRoutine Handler, boolean Add); /** @delegate */ // A delegate type to be used as the handler routine // for SetConsoleCtrlHandler. public delegate boolean HandlerRoutine(int CtrlType); // The control messages sent to the handler routine. public static int CtrlTypes[] = new int[] { 0,/*CTRL_C_EVENT*/ 1,/*CTRL_BREAK_EVENT*/ 2,/*CTRL_CLOSE_EVENT*/ 5,/*CTRL_LOGOFF_EVENT*/ 6 /*CTRL_SHUTDOWN_EVENT*/ }; } //MyWin32 public class MyApp { // A private static handler function in the MyApp class. static boolean Handler(int CtrlType) { String message = "This message should never be seen!"; if ( MyWin32.CtrlTypes[0] == CtrlType) { message = "A CTRL_C_EVENT was raised by the user."; } if (MyWin32.CtrlTypes[1] == CtrlType) { message = "A CTRL_BREAK_EVENT was raised by the user."; } if (MyWin32.CtrlTypes[2] == CtrlType) { message = "A CTRL_CLOSE_EVENT was raised by the user."; } if ( MyWin32.CtrlTypes[3] == CtrlType) { message = "A CTRL_LOGOFF_EVENT was raised by the user."; } if (MyWin32.CtrlTypes[4] == CtrlType) { message = "A CTRL_SHUTDOWN_EVENT was raised by the user."; } // Use interop to display a message for the type of event. Console.WriteLine(message); return true ; } //Handler public static void main(String[] args) { // Use interop to set a console control handler. MyWin32.HandlerRoutine hr = new MyWin32.HandlerRoutine(Handler); MyWin32.SetConsoleCtrlHandler(hr, true); // Give the user some time to raise a few events. Console.WriteLine("Waiting 30 seconds for console ctrl events..."); // The object hr is not referred to again. // The garbage collector can detect that the object has no // more managed references and might clean it up here while // the unmanaged SetConsoleCtrlHandler method is still using it. // Force a garbage collection to demonstrate how the hr // object will be handled. GC.Collect(); GC.WaitForPendingFinalizers(); GC.Collect(); try { Thread.sleep(30000); } catch (InterruptedException e) { } // Display a message to the console when the unmanaged method // has finished its work. Console.WriteLine("Finished!"); // Call GC.KeepAlive(hr) at this point to maintain a reference to hr. // This will prevent the garbage collector from collecting the // object during the execution of the SetConsoleCtrlHandler method. GC.KeepAlive(hr); Console.Read(); } //main } //MyApp
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