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diff --git a/src/vm/hillclimbing.h b/src/vm/hillclimbing.h
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+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+//=========================================================================
+
+//
+// HillClimbing.h
+//
+// Defines classes for the ThreadPool's HillClimbing concurrency-optimization
+// algorithm.
+//
+
+//=========================================================================
+
+#ifndef _HILLCLIMBING_H
+#define _HILLCLIMBING_H
+
+#include "complex.h"
+#include "random.h"
+
+enum HillClimbingStateTransition 
+{
+    Warmup, 
+    Initializing,
+    RandomMove,
+    ClimbingMove,
+    ChangePoint,
+    Stabilizing,
+    Starvation, //used by ThreadpoolMgr
+    ThreadTimedOut, //used by ThreadpoolMgr
+    Undefined,
+};
+
+
+class HillClimbing	
+{
+private:
+    int m_wavePeriod;
+    int m_samplesToMeasure;
+    double m_targetThroughputRatio;
+    double m_targetSignalToNoiseRatio;
+    double m_maxChangePerSecond;
+    double m_maxChangePerSample;
+    int m_maxThreadWaveMagnitude;
+    DWORD m_sampleIntervalLow;
+    double m_threadMagnitudeMultiplier;
+    DWORD m_sampleIntervalHigh;
+    double m_throughputErrorSmoothingFactor;
+    double m_gainExponent;
+    double m_maxSampleError;
+
+    double m_currentControlSetting;
+    LONGLONG m_totalSamples;
+    int m_lastThreadCount;
+    double m_elapsedSinceLastChange; //elapsed seconds since last thread count change
+    double m_completionsSinceLastChange; //number of completions since last thread count change
+
+    double m_averageThroughputNoise;
+
+    double* m_samples;      //Circular buffer of the last m_samplesToMeasure samples
+    double* m_threadCounts; //Thread counts effective at each of m_samples
+
+    unsigned int m_currentSampleInterval;
+    CLRRandom m_randomIntervalGenerator;
+
+    int m_accumulatedCompletionCount;
+    double m_accumulatedSampleDuration;
+
+    void ChangeThreadCount(int newThreadCount, HillClimbingStateTransition transition);
+    void LogTransition(int threadCount, double throughput, HillClimbingStateTransition transition);
+
+    Complex GetWaveComponent(double* samples, int sampleCount, double period);
+
+public:
+    void Initialize();
+    int Update(int currentThreadCount, double sampleDuration, int numCompletions, int* pNewSampleInterval);
+    void ForceChange(int newThreadCount, HillClimbingStateTransition transition);
+};
+
+#define HillClimbingLogCapacity 200
+
+struct HillClimbingLogEntry
+{
+    DWORD TickCount;
+    HillClimbingStateTransition Transition;
+    int NewControlSetting;
+    int LastHistoryCount;
+    float LastHistoryMean;
+};
+
+GARY_DECL(HillClimbingLogEntry, HillClimbingLog, HillClimbingLogCapacity);
+GVAL_DECL(int, HillClimbingLogFirstIndex);
+GVAL_DECL(int, HillClimbingLogSize);
+typedef DPTR(HillClimbingLogEntry) PTR_HillClimbingLogEntry;
+
+#endif