Code:
/ DotNET / DotNET / 8.0 / untmp / whidbey / REDBITS / ndp / clr / src / BCL / System / Runtime / InteropServices / GCHandleCookieTable.cs / 1 / GCHandleCookieTable.cs
// ==++== // // Copyright (c) Microsoft Corporation. All rights reserved. // // ==--== #if MDA_SUPPORTED namespace System.Runtime.InteropServices { using System; using System.Collections; using System.Collections.Generic; using System.Threading; using ObjectHandle = IntPtr; using GCHandleCookie = IntPtr; // Internal class used to map a GCHandle to an IntPtr. Instead of handing out the underlying CLR // handle, we now hand out a cookie that can later be converted back to the CLR handle it // is associated with. internal class GCHandleCookieTable { private const int MaxListSize = 0xFFFFFF; private const uint CookieMaskIndex = 0x00FFFFFF; private const uint CookieMaskSentinal = 0xFF000000; internal GCHandleCookieTable() { m_HandleList = new ObjectHandle[10]; m_CycleCounts = new byte[10]; m_HandleToCookieMap = new Hashtable(); m_FreeIndex = 1; for (int i=0; i < 10; i++) { m_HandleList[i] = ObjectHandle.Zero; m_CycleCounts[i] = 0; } } // Retrieve a cookie for the passed in handle. If no cookie has yet been allocated for // this handle, one will be created. This method is thread safe. internal GCHandleCookie FindOrAddHandle(ObjectHandle handle) { // Don't accept a null object handle if (handle == ObjectHandle.Zero) return GCHandleCookie.Zero; // First see if we already have a cookie for this handle. object tempobj = null; tempobj = m_HandleToCookieMap[handle]; if (tempobj != null) return (GCHandleCookie)tempobj; GCHandleCookie cookie = GCHandleCookie.Zero; // First, try the m_FreeIndex as a quick check int idx = m_FreeIndex; if ((idx < m_HandleList.Length) && (m_HandleList[idx] == ObjectHandle.Zero)) { if (Interlocked.CompareExchange(ref m_HandleList[idx], handle, ObjectHandle.Zero) == ObjectHandle.Zero) { cookie = GetCookieFromData((uint)idx, m_CycleCounts[idx]); // Set our next guess just one higher if valid as this index is no longer a good guess. if (idx+1 < m_HandleList.Length) m_FreeIndex = idx+1; } } // Free index was taken...find an empty entry in the objecthandle list and fill it with the handle if (cookie == GCHandleCookie.Zero) { for (idx = 1; idx < MaxListSize; idx++) { // If we found an empty entry, try to use it. if (m_HandleList[idx] == ObjectHandle.Zero) { if (Interlocked.CompareExchange(ref m_HandleList[idx], handle, ObjectHandle.Zero) == ObjectHandle.Zero) { cookie = GetCookieFromData((uint)idx, m_CycleCounts[idx]); // Set our next guess just one higher if we ended up traversing the array. if (idx+1 < m_HandleList.Length) m_FreeIndex = idx+1; break; } } // Make sure we have enough space in the list to continue the search. if (idx+1 >= m_HandleList.Length) { lock(this) { if (idx+1 >= m_HandleList.Length) { GrowArrays(); } } } } } // If we overflowed the array, we're out of memory. if (cookie == GCHandleCookie.Zero) throw new OutOfMemoryException(Environment.GetResourceString("OutOfMemory_GCHandleMDA")); // Now that we have a cookie - remember it in our hash table. lock (this) { // First check to see if another thread already added the handle. tempobj = m_HandleToCookieMap[handle]; if (tempobj != null) { // The handle has already been added so release the cookie m_HandleList[idx] = ObjectHandle.Zero; cookie = (GCHandleCookie)tempobj; } else { // This handle hasn't been added to the map yet so add it. m_HandleToCookieMap[handle] = cookie; } } return cookie; } // Get a handle. internal ObjectHandle GetHandle(GCHandleCookie cookie) { ObjectHandle oh = ObjectHandle.Zero; if (!ValidateCookie(cookie)) return ObjectHandle.Zero; oh = m_HandleList[GetIndexFromCookie(cookie)]; return oh; } // Remove the handle from the cookie table if it is present. // // IMPORTANT: This method is NOT synchronized so the caller of this function must ensure // it is only called once for a given handle. internal void RemoveHandleIfPresent(ObjectHandle handle) { if (handle == ObjectHandle.Zero) return; object tempobj = m_HandleToCookieMap[handle]; if (tempobj != null) { GCHandleCookie cookie = (GCHandleCookie)tempobj; // Remove it from the array first if (!ValidateCookie(cookie)) return; int index = GetIndexFromCookie(cookie); m_CycleCounts[index]++; m_HandleList[index] = ObjectHandle.Zero; // Remove it from the hashtable last m_HandleToCookieMap.Remove(handle); // Update our guess m_FreeIndex = index; } } private bool ValidateCookie(GCHandleCookie cookie) { int index; byte xorData; GetDataFromCookie(cookie, out index, out xorData); // Validate the index if (index >= MaxListSize) return false; if (index >= m_HandleList.Length) return false; if (m_HandleList[index] == ObjectHandle.Zero) return false; // Validate the xorData byte (this contains the cycle count and appdomain id). byte ADID = (byte)(AppDomain.CurrentDomain.Id % 0xFF); byte goodData = (byte)(m_CycleCounts[index] ^ ADID); if (xorData != goodData) return false; return true; } // Double the size of our arrays - must be called with the lock taken. private void GrowArrays() { int CurrLength = m_HandleList.Length; ObjectHandle[] newHandleList = new ObjectHandle[CurrLength*2]; byte[] newCycleCounts = new byte[CurrLength*2]; Array.Copy(m_HandleList, newHandleList, CurrLength); Array.Copy(m_CycleCounts, newCycleCounts, CurrLength); m_HandleList = newHandleList; m_CycleCounts = newCycleCounts; } // Generate a cookie based on the index, cyclecount, and current domain id. private GCHandleCookie GetCookieFromData(uint index, byte cycleCount) { byte ADID = (byte) (AppDomain.CurrentDomain.Id % 0xFF); return (GCHandleCookie) (((cycleCount ^ ADID) << 24) + index + 1); } // Break down the cookie into its parts private void GetDataFromCookie(GCHandleCookie cookie, out int index, out byte xorData) { uint intCookie = (uint)cookie; index = (int)(intCookie & CookieMaskIndex) - 1; xorData = (byte)((intCookie & CookieMaskSentinal) >> 24); } // Just get the index from the cookie private int GetIndexFromCookie(GCHandleCookie cookie) { uint intCookie = (uint)cookie; return (int)(intCookie & CookieMaskIndex) - 1; } private Hashtable m_HandleToCookieMap; private ObjectHandle[] m_HandleList; private byte[] m_CycleCounts; int m_FreeIndex; } } #endif
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