MemoryPressure.cs source code in C# .NET

Source code for the .NET framework in C#

                        
Code:

                         / 4.0 / 4.0 / untmp / DEVDIV_TFS / Dev10 / Releases / RTMRel / wpf / src / Core / CSharp / MS / Internal / MemoryPressure.cs / 1305600 / 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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