FrequentObjectsStats.hpp

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 * Copyright (c) 1991, 2021 IBM Corp. and others
 *
 * This program and the accompanying materials are made available under
 * the terms of the Eclipse Public License 2.0 which accompanies this
 * distribution and is available at https://www.eclipse.org/legal/epl-2.0/
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 * is available at https://www.apache.org/licenses/LICENSE-2.0.
 *
 * This Source Code may also be made available under the following
 * Secondary Licenses when the conditions for such availability set
 * forth in the Eclipse Public License, v. 2.0 are satisfied: GNU
 * General Public License, version 2 with the GNU Classpath
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 *
 * [1] https://www.gnu.org/software/classpath/license.html
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/**
 * @file
 * @ingroup GC_Stats
 */

#if !defined(FREQUENTOBJECTSSTATS_HPP_)
#define FREQUENTOBJECTSSTATS_HPP_

#include "j9.h"
#include "objectdescription.h"
#include "spacesaving.h"

#include "Base.hpp"
#include "EnvironmentBase.hpp"

#define TOPK_FREQUENT_DEFAULT 10
#define K_TO_SIZE_RATIO 8

/*
 * Keeps track of the most frequent class instantiations
 */

class MM_FrequentObjectsStats : public MM_Base
{
/* Data Members */
public:
	OMRSpaceSaving * _spaceSaving;
	U_32 _topKFrequent;
private:
	J9PortLibrary *_portLibrary;

private:

	/*
	 * Estimates the space necessary to report the top k elements accurately 90% of the time.
	 * Derived from a sample run of Eclipse, which showed that the size necessary to have accurately report the top k
	 * elements was approximately linear.
	 */
	U_32 getSizeForTopKFrequent(U_32 topKFrequent)
	{
		return topKFrequent*K_TO_SIZE_RATIO;
	}

/* Function Members */
public:
	static MM_FrequentObjectsStats *newInstance(MM_EnvironmentBase *env);
	virtual void kill(MM_EnvironmentBase *env);

	/* reset the stats*/
	void clear()
	{
		spaceSavingClear(_spaceSaving);
	}

	/*
	 * Update stats with another class
	 * @param clazz another clazz to record
	 */
	void update(MM_EnvironmentBase *env, omrobjectptr_t object)
	{
		/* Todo: implement ability to do ranking based on total size of object instances, instead
		 * of just number of object instances
		 */

		spaceSavingUpdate(_spaceSaving, J9OBJECT_CLAZZ((J9VMThread *)env->getLanguageVMThread(), object), 1);
	}

	/* Creates a data structure which keeps track of the k most frequent class allocations (estimated probability of 90% of
	 * reporting this accurately (and in the correct order).  The larger k is, the more memory is required
	 * @param portLibrary the port library
	 * @param k the number of frequent objects we'd like to accurately report
	 */
	MM_FrequentObjectsStats(J9PortLibrary *portLibrary, U_32 k=TOPK_FREQUENT_DEFAULT)
		: _spaceSaving(0)
		, _topKFrequent(k)
		,_portLibrary(portLibrary)
	{}


	/* Merges a FrequentObjectStats structures together with this one*/
	void merge(MM_FrequentObjectsStats* frequentObjectsStats);

	void traceStats(MM_EnvironmentBase *env);

protected:
	virtual bool initialize(MM_EnvironmentBase *env);
	virtual void tearDown(MM_EnvironmentBase *env);
};

#endif /* !FREQUENTOBJECTSSTATS_HPP_ */