Code:
/ 4.0 / 4.0 / untmp / DEVDIV_TFS / Dev10 / Releases / RTMRel / ndp / clr / src / BCL / System / Runtime / InteropServices / GCHandleCookieTable.cs / 1305376 / GCHandleCookieTable.cs
// ==++== // // Copyright (c) Microsoft Corporation. All rights reserved. // // ==--== #if MDA_SUPPORTED namespace System.Runtime.InteropServices { using System; using System.Collections.Generic; 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. // NOTE: // this implementation uses a single lock between FindOrAddHandle and RemoveHandleIfPresent which // could create some scalability issues when this MDA is turned on. if this is affecting perf // then additional tuning work will be required. internal class GCHandleCookieTable { private const int InitialHandleCount = 10; private const int MaxListSize = 0xFFFFFF; private const uint CookieMaskIndex = 0x00FFFFFF; private const uint CookieMaskSentinal = 0xFF000000; internal GCHandleCookieTable() { m_HandleList = new ObjectHandle[InitialHandleCount]; m_CycleCounts = new byte[InitialHandleCount]; m_HandleToCookieMap = new Dictionary(InitialHandleCount); m_syncObject = new object(); for (int i = 0; i < InitialHandleCount; 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; GCHandleCookie cookie = GCHandleCookie.Zero; lock (m_syncObject) { // First see if we already have a cookie for this handle. if (m_HandleToCookieMap.ContainsKey(handle)) return m_HandleToCookieMap[handle]; if ((m_FreeIndex < m_HandleList.Length) && (m_HandleList[m_FreeIndex] == ObjectHandle.Zero)) { m_HandleList[m_FreeIndex] = handle; cookie = GetCookieFromData((uint)m_FreeIndex, m_CycleCounts[m_FreeIndex]); // Set our next guess just one higher as this index is now in use. // it's ok if this sets m_FreeIndex > m_HandleList.Length as this condition is // checked at the beginning of the if statement. ++m_FreeIndex; } else { for (m_FreeIndex = 0; m_FreeIndex < MaxListSize; ++m_FreeIndex) { if (m_HandleList[m_FreeIndex] == ObjectHandle.Zero) { m_HandleList[m_FreeIndex] = handle; cookie = GetCookieFromData((uint)m_FreeIndex, m_CycleCounts[m_FreeIndex]); // this will be our next guess for a free index. // it's ok if this sets m_FreeIndex > m_HandleList.Length // since we check for this condition in the if statement. ++m_FreeIndex; break; } if (m_FreeIndex + 1 == m_HandleList.Length) GrowArrays(); } } if (cookie == GCHandleCookie.Zero) throw new OutOfMemoryException(Environment.GetResourceString("OutOfMemory_GCHandleMDA")); // This handle hasn't been added to the map yet so add it. m_HandleToCookieMap.Add(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. // internal void RemoveHandleIfPresent(ObjectHandle handle) { if (handle == ObjectHandle.Zero) return; lock (m_syncObject) { if (m_HandleToCookieMap.ContainsKey(handle)) { GCHandleCookie cookie = m_HandleToCookieMap[handle]; // 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 Dictionary m_HandleToCookieMap; private ObjectHandle[] m_HandleList; private byte[] m_CycleCounts; private int m_FreeIndex; private object m_syncObject; } } #endif // File provided for Reference Use Only by Microsoft Corporation (c) 2007.
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