GC.cs source code in C# .NET

Source code for the .NET framework in C#

                        
Code:

                         / DotNET / DotNET / 8.0 / untmp / whidbey / REDBITS / ndp / clr / src / BCL / System / GC.cs / 3 / GC.cs
                        

                        
                            // ==++== 
//
//   Copyright (c) Microsoft Corporation.  All rights reserved.
//
// ==--== 
/*============================================================
** 
** Class:  GC 
**
** 
** Purpose: Exposes features of the Garbage Collector through
** the class libraries.  This is a class which cannot be
** instantiated.
** 
**
===========================================================*/ 
namespace System { 
    //This class only static members and doesn't require the serializable keyword.
 
    using System;
    using System.Security.Permissions;
    using System.Reflection;
    using System.Security; 
    using System.Threading;
    using System.Runtime.CompilerServices; 
    using System.Runtime.ConstrainedExecution; 
    using System.Reflection.Cache;
 
    // !!!!!!!!!!!!!!!!!!!!!!!
    // make sure you change the def in vm\gc.h
    // if you change this!
    [Serializable] 
    public enum GCCollectionMode
    { 
        Default = 0, 
        Forced = 1,
        Optimized = 2 
    }

    public static class GC
    { 

        [MethodImplAttribute(MethodImplOptions.InternalCall)] 
        internal static extern int nativeGetGCLatencyMode(); 

        [MethodImplAttribute(MethodImplOptions.InternalCall)] 
        internal static extern void nativeSetGCLatencyMode(int newLatencyMode);

        [MethodImplAttribute(MethodImplOptions.InternalCall)]
        private static extern int GetGenerationWR(IntPtr handle); 

        [MethodImplAttribute(MethodImplOptions.InternalCall)] 
        private static extern long nativeGetTotalMemory(); 

        [MethodImplAttribute(MethodImplOptions.InternalCall)] 
        private static extern void nativeCollectGeneration(int generation, int mode);

        [MethodImplAttribute(MethodImplOptions.InternalCall)]
        private static extern int nativeGetMaxGeneration(); 

        [MethodImplAttribute(MethodImplOptions.InternalCall)] 
        [ReliabilityContract(Consistency.WillNotCorruptState, Cer.Success)] 
        private static extern int nativeCollectionCount (int generation);
 
        [MethodImplAttribute(MethodImplOptions.InternalCall)]
        internal static extern bool nativeIsServerGC();

        [MethodImplAttribute(MethodImplOptions.InternalCall)] 
        internal static extern void nativeAddMemoryPressure(UInt64 bytesAllocated);
 
        [MethodImplAttribute(MethodImplOptions.InternalCall)] 
        internal static extern void nativeRemoveMemoryPressure(UInt64 bytesAllocated);
 
        [SecurityPermission(SecurityAction.LinkDemand, UnmanagedCode=true)]
        public static void AddMemoryPressure (long bytesAllocated) {
            if( bytesAllocated <= 0) {
                throw new ArgumentOutOfRangeException("bytesAllocated", 
                        Environment.GetResourceString("ArgumentOutOfRange_NeedPosNum"));
            } 
 
            if( (4 == IntPtr.Size) && (bytesAllocated > Int32.MaxValue) ) {
                throw new ArgumentOutOfRangeException("pressure", 
                        Environment.GetResourceString("ArgumentOutOfRange_MustBeNonNegInt32"));
            }

            nativeAddMemoryPressure((ulong)bytesAllocated); 
        }
 
        [SecurityPermission(SecurityAction.LinkDemand, UnmanagedCode=true)] 
        public static void RemoveMemoryPressure (long bytesAllocated) {
            if( bytesAllocated <= 0) { 
                throw new ArgumentOutOfRangeException("bytesAllocated",
                        Environment.GetResourceString("ArgumentOutOfRange_NeedPosNum"));
            }
 
            if( (4 == IntPtr.Size)  && (bytesAllocated > Int32.MaxValue) ) {
                throw new ArgumentOutOfRangeException("bytesAllocated", 
                        Environment.GetResourceString("ArgumentOutOfRange_MustBeNonNegInt32")); 
            }
 
            nativeRemoveMemoryPressure((ulong) bytesAllocated);
        }

 
        // Returns the generation that obj is currently in.
        // 
        [MethodImplAttribute(MethodImplOptions.InternalCall)] 
        public static extern int GetGeneration(Object obj);
 

        // Forces a collection of all generations from 0 through Generation.
        //
        public static void Collect(int generation) { 
            Collect(generation, GCCollectionMode.Default);
        } 
 
        // Garbage Collect all generations.
        // 
        public static void Collect() {
            //-1 says to GC all generations.
            nativeCollectGeneration(-1, (int)GCCollectionMode.Default);
        } 

        public static void Collect(int generation, GCCollectionMode mode) 
        { 
            if (generation<0)
            { 
                throw new ArgumentOutOfRangeException("generation", Environment.GetResourceString("ArgumentOutOfRange_GenericPositive"));
            }
            if ((mode < GCCollectionMode.Default) || (mode > GCCollectionMode.Optimized))
            { 
                throw new ArgumentOutOfRangeException(Environment.GetResourceString("ArgumentOutOfRange_Enum"));
            } 
 
            nativeCollectGeneration(generation, (int)mode);
        } 

        [ReliabilityContract(Consistency.WillNotCorruptState, Cer.Success)]
        public static int CollectionCount (int generation) {
            if (generation<0) { 
                throw new ArgumentOutOfRangeException("generation", Environment.GetResourceString("ArgumentOutOfRange_GenericPositive"));
            } 
            return nativeCollectionCount(generation); 

        } 


        // This method DOES NOT DO ANYTHING in and of itself.  It's used to
        // prevent a finalizable object from losing any outstanding references 
        // a touch too early.  The JIT is very aggressive about keeping an
        // object's lifetime to as small a window as possible, to the point 
        // where a 'this' pointer isn't considered live in an instance method 
        // unless you read a value from the instance.  So for finalizable
        // objects that store a handle or pointer and provide a finalizer that 
        // cleans them up, this can cause subtle races with the finalizer
        // thread.  This isn't just about handles - it can happen with just
        // about any finalizable resource.
        // 
        // Users should insert a call to this method near the end of a
        // method where they must keep an object alive for the duration of that 
        // method, up until this method is called.  Here is an example: 
        //
        // "...all you really need is one object with a Finalize method, and a 
        // second object with a Close/Dispose/Done method.  Such as the following
        // contrived example:
        //
        // class Foo { 
        //    Stream stream = ...;
        //    protected void Finalize() { stream.Close(); } 
        //    void Problem() { stream.MethodThatSpansGCs(); } 
        //    static void Main() { new Foo().Problem(); }
        // } 
        //
        //
        // In this code, Foo will be finalized in the middle of
        // stream.MethodThatSpansGCs, thus closing a stream still in use." 
        //
        // If we insert a call to GC.KeepAlive(this) at the end of Problem(), then 
        // Foo doesn't get finalized and the stream says open. 
        [MethodImplAttribute(MethodImplOptions.InternalCall)]
        [ReliabilityContract(Consistency.WillNotCorruptState, Cer.Success)] 
        public static extern void KeepAlive(Object obj);

        // Returns the generation in which wo currently resides.
        // 
        public static int GetGeneration(WeakReference wo) {
            int result = GetGenerationWR(wo.m_handle); 
            KeepAlive(wo); 
            return result;
        } 

        // Returns the maximum GC generation.  Currently assumes only 1 heap.
        //
        public static int MaxGeneration { 
            get { return nativeGetMaxGeneration(); }
        } 
 
        [MethodImplAttribute(MethodImplOptions.InternalCall)]
        public static extern void WaitForPendingFinalizers(); 

        // Indicates that the system should not call the Finalize() method on
        // an object that would normally require this call.
        // Has the DynamicSecurityMethodAttribute custom attribute to prevent 
        // inlining of the caller.
        [MethodImplAttribute(MethodImplOptions.InternalCall)] 
        [ReliabilityContract(Consistency.WillNotCorruptState, Cer.Success)] 
        internal static extern void nativeSuppressFinalize(Object o);
 
        [ReliabilityContract(Consistency.WillNotCorruptState, Cer.Success)]
        public static void SuppressFinalize(Object obj) {
            if (obj == null)
                throw new ArgumentNullException("obj"); 
            nativeSuppressFinalize(obj);
        } 
 
        // Indicates that the system should call the Finalize() method on an object
        // for which SuppressFinalize has already been called. The other situation 
        // where calling ReRegisterForFinalize is useful is inside a finalizer that
        // needs to resurrect itself or an object that it references.
        // Has the DynamicSecurityMethodAttribute custom attribute to prevent
        // inlining of the caller. 
        [MethodImplAttribute(MethodImplOptions.InternalCall)]
        private static extern void nativeReRegisterForFinalize(Object o); 
 
        public static void ReRegisterForFinalize(Object obj) {
            if (obj == null) 
                throw new ArgumentNullException("obj");
            nativeReRegisterForFinalize(obj);
        }
 
        // Returns the total number of bytes currently in use by live objects in
        // the GC heap.  This does not return the total size of the GC heap, but 
        // only the live objects in the GC heap. 
        //
        public static long GetTotalMemory(bool forceFullCollection) { 
            long size = nativeGetTotalMemory();
            if (!forceFullCollection)
                return size;
            // If we force a full collection, we will run the finalizers on all 
            // existing objects and do a collection until the value stabilizes.
            // The value is "stable" when either the value is within 5% of the 
            // previous call to nativeGetTotalMemory, or if we have been sitting 
            // here for more than x times (we don't want to loop forever here).
            int reps = 20;  // Number of iterations 
            long newSize = size;
            float diff;
            do {
                GC.WaitForPendingFinalizers(); 
                GC.Collect();
                size = newSize; 
                newSize = nativeGetTotalMemory(); 
                diff = ((float)(newSize - size)) / size;
            } while (reps-- > 0 && !(-.05 < diff && diff < .05)); 
            return newSize;
        }

        [MethodImplAttribute(MethodImplOptions.InternalCall)] 
        private static extern void SetCleanupCache();
 
        private static ClearCacheHandler m_cacheHandler; 
        private static readonly Object locker = new Object();
 
        internal static event ClearCacheHandler ClearCache {
            add {
                lock (locker) {
                    m_cacheHandler+=value; 
                    SetCleanupCache();
                } 
            } 
            remove {
                lock (locker) 
                    m_cacheHandler-=value;
            }
        }
 
        //This method is called from native code.  If you update the signature, please also update
        //mscorlib.h and COMUtilNative.cpp 
        internal static void FireCacheEvent() { 
            BCLDebug.Trace("CACHE", "Called FileCacheEvent");
            ClearCacheHandler handler = Interlocked.Exchange(ref m_cacheHandler, null); 
            if (handler!=null) {
                handler(null, null);
            }
        } 
    }
}

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