core-server/src/main/java/org/glassfish/jersey/server/internal/monitoring/core/ReservoirConstants.java

/*
 * Copyright 2015, 2021 Oracle and/or its affiliates. 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.
 */

package org.glassfish.jersey.server.internal.monitoring.core;

import java.security.AccessController;
import java.security.PrivilegedAction;
import java.util.logging.Level;
import java.util.logging.Logger;

import org.glassfish.jersey.server.ServerProperties;

/**
 * The constants that determine the behaviour of sliding windows and their trimmers.
 *
 * @author Stepan Vavra
 */
public final class ReservoirConstants {

    private static final int DEFAULT_COLLISION_BUFFER_POWER = 8;

    /**
     * Allow for 2^that many duplicate ticks before throwing away measurements.
     * This value is by default {@link DEFAULT_COLLISION_BUFFER_POWER}, but it can be configured
     * with {@link COLLISION_BUFFER_POWER_JVM_ARG} JVM argument
     */
    public static final int COLLISION_BUFFER_POWER;

    /**
     * The size of the collision buffer derived from the collision buffer power.
     */
    public static final int COLLISION_BUFFER;

    /**
     * Only trim on updating once every N.
     */
    public static final int TRIM_THRESHOLD = 256;

    static {
        PrivilegedAction<Integer> action = new PrivilegedAction<Integer>() {
            @Override
            public Integer run() {
                return Integer.getInteger(ServerProperties.COLLISION_BUFFER_POWER_JVM_ARG, DEFAULT_COLLISION_BUFFER_POWER);
            }
        };
        COLLISION_BUFFER_POWER = AccessController.doPrivileged(action);
        COLLISION_BUFFER = 1 << COLLISION_BUFFER_POWER; // 256
    }

    private ReservoirConstants() {
        throw new AssertionError("Instantiation not allowed.");
    }
}