Code:
/ DotNET / DotNET / 8.0 / untmp / WIN_WINDOWS / lh_tools_devdiv_wpf / Windows / wcp / Core / MS / Internal / MemoryPressure.cs / 1 / MemoryPressure.cs
using System; using System.Diagnostics; using System.Threading; using MS.Utility; namespace MS.Internal { ////// The MemoryPressure class internally replaces the GC.AddMemoryPressure, /// GC.RemoveMemoryPressure API from the CLR. As of Whidbey Beta 2 the performance /// of that API is not sufficient for our needs and should not be used in Avalon. /// /// Avalon currently only tracks unmanaged memory pressure related to Images. /// The implementation of this class exploits this by using a timer-based /// tracking scheme. It assumes that the unmanaged memory it is tracking /// is allocated in batches, held onto for a long time, and released all at once /// We have profiled a variety of scenarios and found images do work this way /// /// Note this class is thread-safe /// internal static class MemoryPressure { static MemoryPressure() { _collectionTimer = new Stopwatch(); _allocationTimer = new Stopwatch(); } ////// Add a number of bytes to the total memory pressure /// /// internal static void Add(long bytesAllocated) { if (bytesAllocated < 0) { throw new ArgumentOutOfRangeException("bytesAllocated"); } // // Note that AddToTotal and ProcessAdd are not in a critical // section. We actually don't care if other threads change // the value of _totalMemory between the calls. // AddToTotal(bytesAllocated); ProcessAdd(); } ////// Remove a number of bytes to the total memory pressure /// /// internal static void Remove(long bytesRemoved) { if (bytesRemoved < 0) { throw new ArgumentOutOfRangeException("bytesRemoved"); } AddToTotal(-bytesRemoved); } ////// Check the timers and decide if enough time has elapsed to /// force a collection /// private static void ProcessAdd() { bool shouldCollect = false; if (_totalMemory >= INITIAL_THRESHOLD) { // // need to synchronize access to the timers, both for the integrity // of the elapsed time and to ensure they are reset and started // properly // lock (lockObj) { // // if it's been long enough since the last allocation // or too long since the last forced collection, collect // if (_allocationTimer.ElapsedMilliseconds >= INTER_ALLOCATION_THRESHOLD || (_collectionTimer.ElapsedMilliseconds > MAX_TIME_BETWEEN_COLLECTIONS)) { _collectionTimer.Reset(); _collectionTimer.Start(); shouldCollect = true; } _allocationTimer.Reset(); _allocationTimer.Start(); } // // now that we're out of the lock do the collection // if (shouldCollect) { Collect(); } } return; } ////// Forces a collection. /// private static void Collect() { // // for now only force Gen 2 GCs to ensure we clean up memory // These will be forced infrequently and the memory we're tracking // is very long lived so it's ok // GC.Collect(2); } ////// Adds the given amount to _totalMemory in a thread-safe manner using the /// CompareExchange synchronization primitive /// private static void AddToTotal(long delta) { long initialValue; long newValue; do { initialValue = _totalMemory; newValue = initialValue + delta; // // Check for overflow of _totalMemory. // Nothing can allocate more than Int64.MaxValue bytes // so this theoretically can't happen if the caller is // well-behaved. This only applies when delta is positive. // Debug.Assert(delta < 0 || initialValue < Int64.MaxValue - delta); Debug.Assert(newValue >= 0); // CompareExchange will replace _totalMemory with newValue only if // _totalMemory equals initialValue. It always returns the current // value of _totalMemory. // // If initialValue does not equal the return value from CompareExchange // this means that another thread has modified _totalMemory and we need // to try again. } while (initialValue != Interlocked.CompareExchange( ref _totalMemory, newValue, initialValue)); } private static readonly Object lockObj = new Object(); private static long _totalMemory; private static Stopwatch _collectionTimer; // time since last collection private static Stopwatch _allocationTimer; // time since last allocation // // About the thresholds: // For the inter-allocation threshold 850ms is the longest time between allocations on a high-end // machine for an image application loading many large (several M pixel) images continuously. // This falls well below user-interaction time (which is on the order of several seconds) so it // differentiates nicely between the two // // The initial threshold of 1MB is so we don't force GCs when the total amount of unmanaged memory // isn't a big deal. The point of this code is to stop unmanaged memory from spiraling out of control // at that point it's typically in the 10s of MBs. This threshold thus could potentially be increased // but current testing shows it is adequate. // // The max time between collections was set to 30 sec because that is a 'long time' - this is // for the case where allocations (and frees) of images are happening continously without // pause - we haven't seen scenarios that do this yet so it's possible this threshold could also // be increased // private const int INITIAL_THRESHOLD = 0x100000; // 1 MB initial threshold private const int INTER_ALLOCATION_THRESHOLD = 850; // ms allowed between allocations private const int MAX_TIME_BETWEEN_COLLECTIONS = 30000; // ms between collections } } // File provided for Reference Use Only by Microsoft Corporation (c) 2007. // Copyright (c) Microsoft Corporation. All rights reserved.
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