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Inconsistent MemoryCache stats #116193

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Inconsistent MemoryCache stats #116193

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63d84f9
Inconsistent MemoryCache stats
pedrobsaila Jun 1, 2025
de19fab
move destructor from Stats to StatsHandle
pedrobsaila Jun 1, 2025
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49 changes: 28 additions & 21 deletions src/libraries/Microsoft.Extensions.Caching.Memory/src/MemoryCache.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -27,10 +27,10 @@ public class MemoryCache : IMemoryCache

private readonly MemoryCacheOptions _options;

private readonly List<WeakReference<Stats>>? _allStats;
private readonly List<Stats>? _allStats;
private long _accumulatedHits;
private long _accumulatedMisses;
private readonly ThreadLocal<Stats>? _stats;
private readonly ThreadLocal<StatsHandle>? _stats;
private CoherentState _coherentState;
private bool _disposed;
private DateTime _lastExpirationScan;
Expand Down Expand Up @@ -59,8 +59,8 @@ public MemoryCache(IOptions<MemoryCacheOptions> optionsAccessor, ILoggerFactory

if (_options.TrackStatistics)
{
_allStats = new List<WeakReference<Stats>>();
_stats = new ThreadLocal<Stats>(() => new Stats(this));
_allStats = new List<Stats>();
_stats = new ThreadLocal<StatsHandle>(() => new StatsHandle(this));
}

_lastExpirationScan = UtcNow;
Expand Down Expand Up @@ -406,34 +406,46 @@ void ScheduleTask(DateTime utcNow)
long hits = _accumulatedHits;
long misses = _accumulatedMisses;

foreach (WeakReference<Stats> wr in _allStats)
foreach (Stats stats in _allStats)
{
if (wr.TryGetTarget(out Stats? stats))
{
hits += Volatile.Read(ref stats.Hits);
misses += Volatile.Read(ref stats.Misses);
}
hits += Volatile.Read(ref stats.Hits);
misses += Volatile.Read(ref stats.Misses);
}

return (hits, misses);
}
}

private Stats GetStats() => _stats!.Value!;
private Stats GetStats() => _stats!.Value!.Stats;

internal class StatsHandle
{
public StatsHandle(MemoryCache memoryCache)
{
Stats = new Stats(memoryCache, this);
}

public Stats Stats { get; private set; }

~StatsHandle() => Stats.RemoveFromStats();
}


internal sealed class Stats
{
private readonly MemoryCache _memoryCache;
public long Hits;
public long Misses;
public WeakReference<StatsHandle> Handle { get; private set; }

public Stats(MemoryCache memoryCache)
public Stats(MemoryCache memoryCache, StatsHandle statsHandle)
{
Handle = new WeakReference<StatsHandle>(statsHandle);
_memoryCache = memoryCache;
_memoryCache.AddToStats(this);
}

~Stats() => _memoryCache.RemoveFromStats(this);
internal void RemoveFromStats() => _memoryCache.RemoveFromStats(this);
}

private void RemoveFromStats(Stats current)
Expand All @@ -443,21 +455,16 @@ private void RemoveFromStats(Stats current)
_accumulatedHits += Volatile.Read(ref current.Hits);
_accumulatedMisses += Volatile.Read(ref current.Misses);

List<WeakReference<Stats>> all = _allStats;
for (int i = all.Count - 1; i >= 0; i--)
{
if (!all[i].TryGetTarget(out _))
all.RemoveAt(i);
}
all.TrimExcess();
_allStats.RemoveAll(static s => !s.Handle.TryGetTarget(out _));
_allStats.TrimExcess();
}
}

private void AddToStats(Stats current)
{
lock (_allStats!)
{
_allStats.Add(new WeakReference<Stats>(current));
_allStats.Add(current);
}
}

Expand Down
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