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Tensorics is a java framework which uses a tensor as a central object. A tensor represents a set of values placed in an N-dimensional space. Wherever you are tempted to use maps of maps, a tensor might be a good choice ;-) Tensorics provides methods to create, transform and performing calculations with those tensors.

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// @formatter:off
 /*******************************************************************************
 *
 * This file is part of tensorics.
 * 
 * Copyright (c) 2008-2011, CERN. All rights reserved.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 * 
 ******************************************************************************/
// @formatter:on

package org.tensorics.core.util;

import java.io.PrintStream;
import java.util.List;

/**
 * To be used for testing. Will contain the actual state of the system and provides methods to print it.
 * 
 * @author kfuchsbe
 */
public final class SystemState {

    private static final int GC_ITERATIONS = 10;

    private static final int KILOBYTE_FACTOR = 1024;

    private final long memoryUsageInB;
    private final long timeInMillis;
    private final boolean delta;

    private SystemState(long memoryUsageInKB, long timeInMillis, boolean delta) {
        super();
        this.memoryUsageInB = memoryUsageInKB;
        this.timeInMillis = timeInMillis;
        this.delta = delta;
    }

    public static SystemState currentTimeAfterGc() {
        long memoryUsage = memoryUsageInByte();
        return new SystemState(memoryUsage, System.currentTimeMillis(), false);
    }

    public static SystemState currentTimeBeforeGc() {
        long time = System.currentTimeMillis();
        return new SystemState(memoryUsageInByte(), time, false);
    }

    public static long memoryUsageInByte() {
        for (int i = 0; i < GC_ITERATIONS; i++) {
            System.gc(); // NOSONAR benchmarking code
        }
        Runtime runtime = Runtime.getRuntime();
        return (runtime.totalMemory() - runtime.freeMemory());
    }

    public SystemState minus(SystemState other) {
        return new SystemState(memoryUsageInB - other.memoryUsageInB, timeInMillis - other.timeInMillis, true);
    }

    public void printTo(PrintStream stream) {
        stream.println(prefix() + "memory : " + getMemoryUsageInKB() + " [kB]");
        stream.println(prefix() + "time : " + timeInMillis + " [millisec]");
    }

    public void printToStdOut() {
        printTo(System.out);
    }

    private String prefix() {
        if (delta) {
            return "delta ";
        }
        return "";
    }

    public long getMemoryUsageInKB() {
        return memoryUsageInB / KILOBYTE_FACTOR;
    }

    public long getMemoryUsageInB() {
        return memoryUsageInB;
    }

    public long getTimeInMillis() {
        return timeInMillis;
    }

    public static void printStates(List states) {
        printStatesTo(states, System.out);
    }

    public static void printStatesTo(List states, PrintStream stream) {
        stream.println("Step \ttime [ms] \tmem [byte]"); // NOSONAR
        int step = 0;
        for (SystemState result : states) {
            stream.println(step++ + "\t" + result.getTimeInMillis() + "\t" + result.getMemoryUsageInB()); // NOSONAR
        }
    }

}