Code:
/ 4.0 / 4.0 / untmp / DEVDIV_TFS / Dev10 / Releases / RTMRel / ndp / fx / src / CommonUI / System / Drawing / Advanced / SystemColorTracker.cs / 1305376 / SystemColorTracker.cs
//------------------------------------------------------------------------------ //// Copyright (c) Microsoft Corporation. All rights reserved. // //----------------------------------------------------------------------------- namespace System.Drawing.Internal { using System.Diagnostics; using System.Diagnostics.CodeAnalysis; using System; using System.Drawing; using Microsoft.Win32; using System.Runtime.InteropServices; using System.ComponentModel; // Keeps track of objects that need to be notified of system color change events. // Mostly this means maintaining a list of weak references. internal class SystemColorTracker { // when I tried the self host, it went over 500 but never over 1000. private static int INITIAL_SIZE = 200; // If it gets this big, I seriously miscalculated the performance of this object. private static int WARNING_SIZE = 100000; private static float EXPAND_THRESHOLD = 0.75f; private static int EXPAND_FACTOR = 2; private static WeakReference[] list = new WeakReference[INITIAL_SIZE]; private static int count = 0; private static bool addedTracker; // There's no such thing as a delegate to a static method, // so we need to create an instance of something. private SystemColorTracker() { } [SuppressMessage("Microsoft.Reliability", "CA2002:DoNotLockOnObjectsWithWeakIdentity")] internal static void Add(ISystemColorTracker obj) { lock (typeof(SystemColorTracker)) { Debug.Assert(list != null, "List is null"); Debug.Assert(list.Length > 0, "INITIAL_SIZE was initialized after list"); if (list.Length == count) { GarbageCollectList(); } if (!addedTracker) { addedTracker = true; SystemEvents.UserPreferenceChanged += new UserPreferenceChangedEventHandler(OnUserPreferenceChanged); } // Strictly speaking, we should grab a lock on this class. But since the chances // of a problem are so low, the consequences so minimal (something will get accidentally dropped // from the list), and the performance of locking so lousy, we'll risk it. int index = count; count++; // COM+ takes forever to Finalize() weak references, so it pays to reuse them. if (list[index] == null) list[index] = new WeakReference(obj); else { Debug.Assert(list[index].Target == null, "Trying to reuse a weak reference that isn't broken yet: list[" + index + "], length =" + list.Length); list[index].Target = obj; } } } private static void CleanOutBrokenLinks() { // Partition the list -- valid references in the low indices, broken references in the high indices. // This is taken straight out of Sedgewick (p. 118 on quicksort). // Basic idea is to find a broken reference on the left side of the list, and swap it with // a valid reference on the right int right = list.Length - 1; int left = 0; int length = list.Length; // Loop invariant: everything to the left of "left" is a valid reference, // and anything to the right of "right" is broken. for (;;) { while (left < length && list[left].Target != null) left++; while (right >= 0 && list[right].Target == null) right--; if (left >= right) { count = left; break; } WeakReference temp = list[left]; list[left] = list[right]; list[right] = temp; left++; right--; } Debug.Assert(count >= 0 && count <= list.Length, "count not a legal index into list"); #if DEBUG // Check loop invariant. // We'd like to assert that any index < count contains a valid pointer, // but since garbage collection can happen at any time, it may have been broken // after we partitioned it. // // for (int i = 0; i < count; i++) { // Debug.Assert(list[i].Target != null, "Null found on the left side of the list"); // } for (int i = count; i < list.Length; i++) { Debug.Assert(list[i].Target == null, "Partitioning didn't work"); } #endif } private static void GarbageCollectList() { CleanOutBrokenLinks(); if (count / (float) list.Length > EXPAND_THRESHOLD) { WeakReference[] newList = new WeakReference[list.Length * EXPAND_FACTOR]; list.CopyTo(newList, 0); list = newList; if (list.Length >= WARNING_SIZE) { Debug.Fail("SystemColorTracker is using way more memory than expected."); } } } private static void OnUserPreferenceChanged(object sender, UserPreferenceChangedEventArgs e) { // Update pens and brushes if (e.Category == UserPreferenceCategory.Color) { for (int i = 0; i < count; i++) { Debug.Assert(list[i] != null, "null value in active part of list"); ISystemColorTracker tracker = (ISystemColorTracker) list[i].Target; if (tracker != null) { // If object still around tracker.OnSystemColorChanged(); } } } } } } // File provided for Reference Use Only by Microsoft Corporation (c) 2007.
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