GcHandle.cs source code in C# .NET

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/ DotNET / DotNET / 8.0 / untmp / whidbey / REDBITS / ndp / clr / src / BCL / System / Runtime / InteropServices / GcHandle.cs / 1 / GcHandle.cs

                            // ==++== 
//
//   Copyright (c) Microsoft Corporation.  All rights reserved.
//
// ==--== 
namespace System.Runtime.InteropServices
{ 
    using System; 
    using System.Security.Permissions;
    using System.Runtime.CompilerServices; 
    using System.Threading;

    // These are the types of handles used by the EE.  IMPORTANT: These must
    // match the definitions in ObjectHandle.h in the EE. 
    [Serializable]
[System.Runtime.InteropServices.ComVisible(true)] 
    public enum GCHandleType 
    {
        Weak = 0, 
        WeakTrackResurrection = 1,
        Normal = 2,
        Pinned = 3
    } 

    // This class allows you to create an opaque, GC handle to any 
    // COM+ object. A GC handle is used when an object reference must be 
    // reachable from unmanaged memory.  There are 3 kinds of roots:
    // Normal - keeps the object from being collected. 
    // Weak - allows object to be collected and handle contents will be zeroed.
    //          Weak references are zeroed before the finalizer runs, so if the
    //          object is resurrected in the finalizer the weak reference is
    //          still zeroed. 
    // WeakTrackResurrection - Same as weak, but stays until after object is
    //          really gone. 
    // Pinned - same as normal, but allows the address of the actual object 
    //          to be taken.
    // 

    [StructLayout(LayoutKind.Sequential)]
[System.Runtime.InteropServices.ComVisible(true)]
    public struct GCHandle 
    {
        internal static readonly IntPtr InvalidCookie = new IntPtr(unchecked((int)0xFFFFFFFF)); 
 
#if MDA_SUPPORTED
        static GCHandle() 
        {
            s_probeIsActive = Mda.IsInvalidGCHandleCookieProbeEnabled();
            if (s_probeIsActive)
                s_cookieTable = new GCHandleCookieTable(); 
        }
#endif 
 
        // Allocate a handle storing the object and the type.
        internal GCHandle(Object value, GCHandleType type) 
        {
            m_handle = InternalAlloc(value, type);

            // Record if the handle is pinned. 
            if (type == GCHandleType.Pinned)
                SetIsPinned(); 
        } 

        // Used in the conversion functions below. 
        internal GCHandle(IntPtr handle)
        {
            InternalCheckDomain(handle);
            m_handle = handle; 
        }
 
        // Creates a new GC handle for an object. 
        //
        // value - The object that the GC handle is created for. 
        // type - The type of GC handle to create.
        //
        // returns a new GC handle that protects the object.
        [SecurityPermissionAttribute(SecurityAction.LinkDemand, Flags=SecurityPermissionFlag.UnmanagedCode)] 
        public static GCHandle Alloc(Object value)
        { 
            return new GCHandle(value, GCHandleType.Normal); 
        }
 
        [SecurityPermissionAttribute(SecurityAction.LinkDemand, Flags=SecurityPermissionFlag.UnmanagedCode)]
        public static GCHandle Alloc(Object value, GCHandleType type)
        {
            return new GCHandle(value, type); 
        }
 
 
        // Frees a GC handle.
        [SecurityPermissionAttribute(SecurityAction.LinkDemand, Flags=SecurityPermissionFlag.UnmanagedCode)] 
        public void Free()
        {
            // Copy the handle instance member to a local variable. This is required to prevent
            // race conditions releasing the handle. 
            IntPtr handle = m_handle;
 
            // Free the handle if it hasn't already been freed. 
            if (handle != IntPtr.Zero && Interlocked.CompareExchange(ref m_handle, IntPtr.Zero, handle) == handle)
            { 
#if WIN32
                InternalFree((IntPtr)(((int)handle) & ~1));
#else
                InternalFree((IntPtr)(((long)handle) & ~1L)); 
#endif
 
#if MDA_SUPPORTED 
                // If this handle was passed out to unmanaged code, we need to remove it
                // from the cookie table. 
                if (s_probeIsActive)
                    s_cookieTable.RemoveHandleIfPresent(handle);
#endif
            } 
            else
            { 
                throw new InvalidOperationException(Environment.GetResourceString("InvalidOperation_HandleIsNotInitialized")); 
            }
        } 

        // Target property - allows getting / updating of the handle's referent.
        public Object Target
        { 
            [SecurityPermissionAttribute(SecurityAction.LinkDemand, Flags=SecurityPermissionFlag.UnmanagedCode)]
            get 
            { 
                // Check if the handle was never initialized or was freed.
                if (m_handle == IntPtr.Zero) 
                    throw new InvalidOperationException(Environment.GetResourceString("InvalidOperation_HandleIsNotInitialized"));

                return InternalGet(GetHandleValue());
            } 

            [SecurityPermissionAttribute(SecurityAction.LinkDemand, Flags=SecurityPermissionFlag.UnmanagedCode)] 
            set 
            {
                // Check if the handle was never initialized or was freed. 
                if (m_handle == IntPtr.Zero)
                    throw new InvalidOperationException(Environment.GetResourceString("InvalidOperation_HandleIsNotInitialized"));

                InternalSet(GetHandleValue(), value, IsPinned()); 
            }
        } 
 
        // Retrieve the address of an object in a Pinned handle.  This throws
        // an exception if the handle is any type other than Pinned. 
        [SecurityPermissionAttribute(SecurityAction.LinkDemand, Flags=SecurityPermissionFlag.UnmanagedCode)]
        public IntPtr AddrOfPinnedObject()
        {
            // Check if the handle was not a pinned handle. 
            if (!IsPinned())
            { 
                // Check if the handle was never initialized for was freed. 
                if (m_handle == IntPtr.Zero)
                    throw new InvalidOperationException(Environment.GetResourceString("InvalidOperation_HandleIsNotInitialized")); 

                // You can only get the address of pinned handles.
                throw new InvalidOperationException(Environment.GetResourceString("InvalidOperation_HandleIsNotPinned"));
            } 

            // Get the address. 
            return InternalAddrOfPinnedObject(GetHandleValue()); 
        }
 
        // Determine whether this handle has been allocated or not.
        public bool IsAllocated
        {
            get 
            {
                return m_handle != IntPtr.Zero; 
            } 
        }
 
        // Used to create a GCHandle from an int.  This is intended to
        // be used with the reverse conversion.
        [SecurityPermissionAttribute(SecurityAction.LinkDemand, Flags=SecurityPermissionFlag.UnmanagedCode)]
        public static explicit operator GCHandle(IntPtr value) 
        {
            return FromIntPtr(value); 
        } 

        [SecurityPermissionAttribute(SecurityAction.LinkDemand, Flags=SecurityPermissionFlag.UnmanagedCode)] 
        public static GCHandle FromIntPtr(IntPtr value)
        {
            if (value == IntPtr.Zero)
                throw new InvalidOperationException(Environment.GetResourceString("InvalidOperation_HandleIsNotInitialized")); 

            IntPtr handle = value; 
 
#if MDA_SUPPORTED
            if (s_probeIsActive) 
            {
                // Make sure this cookie matches up with a GCHandle we've passed out a cookie for.
                handle = s_cookieTable.GetHandle(value);
                if (IntPtr.Zero == handle) 
                {
                    // Fire an MDA if we were unable to retrieve the GCHandle. 
                    Mda.FireInvalidGCHandleCookieProbe(value); 
                    return new GCHandle(IntPtr.Zero);
                } 
            }
#endif

            return new GCHandle(handle); 
        }
 
        // Used to get the internal integer representation of the handle out. 
        public static explicit operator IntPtr(GCHandle value)
        { 
            return ToIntPtr(value);
        }

        public static IntPtr ToIntPtr(GCHandle value) 
        {
#if MDA_SUPPORTED 
            if (s_probeIsActive) 
            {
                // Remember that we passed this GCHandle out by storing the cookie we returned so we 
                //  can later validate.
                return s_cookieTable.FindOrAddHandle(value.m_handle);
            }
#endif 
            return value.m_handle;
        } 
 
        public override int GetHashCode()
        { 
            return (int)m_handle;
        }

        public override bool Equals(Object o) 
        {
            GCHandle hnd; 
 
            // Check that o is a GCHandle first
            if(o == null || !(o is GCHandle)) 
                return false;
            else
                hnd = (GCHandle) o;
 
            return m_handle == hnd.m_handle;
        } 
 
        public static bool operator ==(GCHandle a, GCHandle b)
        { 
            return a.m_handle == b.m_handle;
        }

        public static bool operator !=(GCHandle a, GCHandle b) 
        {
            return a.m_handle != b.m_handle; 
        } 

        internal IntPtr GetHandleValue() 
        {
#if WIN32
            return new IntPtr(((int)m_handle) & ~1);
#else 
            return new IntPtr(((long)m_handle) & ~1L);
#endif 
        } 

        internal bool IsPinned() 
        {
#if WIN32
            return (((int)m_handle) & 1) != 0;
#else 
            return (((long)m_handle) & 1) != 0;
#endif 
        } 

        internal void SetIsPinned() 
        {
#if WIN32
            m_handle = new IntPtr(((int)m_handle) | 1);
#else 
            m_handle = new IntPtr(((long)m_handle) | 1L);
#endif 
        } 

        // Internal native calls that this implementation uses. 
        [MethodImplAttribute(MethodImplOptions.InternalCall)]
        internal static extern IntPtr InternalAlloc(Object value, GCHandleType type);
        [MethodImplAttribute(MethodImplOptions.InternalCall)]
        internal static extern void InternalFree(IntPtr handle); 
        [MethodImplAttribute(MethodImplOptions.InternalCall)]
        internal static extern Object InternalGet(IntPtr handle); 
        [MethodImplAttribute(MethodImplOptions.InternalCall)] 
        internal static extern void InternalSet(IntPtr handle, Object value, bool isPinned);
        [MethodImplAttribute(MethodImplOptions.InternalCall)] 
        internal static extern Object InternalCompareExchange(IntPtr handle, Object value, Object oldValue, bool isPinned);
        [MethodImplAttribute(MethodImplOptions.InternalCall)]
        internal static extern IntPtr InternalAddrOfPinnedObject(IntPtr handle);
        [MethodImplAttribute(MethodImplOptions.InternalCall)] 
        internal static extern void InternalCheckDomain(IntPtr handle);
 
        // The actual integer handle value that the EE uses internally. 
        private IntPtr m_handle;
 
#if MDA_SUPPORTED
        // The GCHandle cookie table.
        static private GCHandleCookieTable s_cookieTable = null;
        static private bool s_probeIsActive = false; 
#endif
    } 
}
                        

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