com.cloudera.oryx.common.random.RandomManager.java Source code

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Here is the source code for com.cloudera.oryx.common.random.RandomManager.java

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/*
 * Copyright (c) 2014, Cloudera, Inc. All Rights Reserved.
 *
 * Cloudera, Inc. licenses this file to you 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
 *
 * This software 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.
 */

package com.cloudera.oryx.common.random;

import java.util.Map;
import java.util.WeakHashMap;

import org.apache.commons.math3.random.RandomGenerator;
import org.apache.commons.math3.random.Well19937c;

/**
 * Manages random number generation. Allows resetting RNGs to a known state for testing.
 */
public final class RandomManager {

    private static final long TEST_SEED = 1_234_567_890_123_456_789L;

    private static final Map<RandomGenerator, Boolean> INSTANCES = new WeakHashMap<>();
    private static boolean useTestSeed;

    private RandomManager() {
    }

    /**
     * @return a new, seeded {@link RandomGenerator}
     */
    public static RandomGenerator getRandom() {
        if (useTestSeed) {
            // No need to track instances anymore
            return new Well19937c(TEST_SEED);
        }
        RandomGenerator random = new Well19937c();
        synchronized (INSTANCES) {
            INSTANCES.put(random, Boolean.TRUE); // Value does not matter
        }
        return random;
    }

    /**
     * <em>Only call in test code.</em> Causes all known instances of {@link RandomGenerator}, and future ones,
     * to be started from a fixed seed. This is useful for making tests deterministic.
     */
    public static void useTestSeed() {
        useTestSeed = true;
        synchronized (INSTANCES) {
            for (RandomGenerator random : INSTANCES.keySet()) {
                random.setSeed(TEST_SEED);
            }
            INSTANCES.clear();
        }
    }

}