Logback: the reliable, generic, fast and flexible logging framework.
Copyright (C) 1999-2015, QOS.ch. All rights reserved.
This program and the accompanying materials are dual-licensed under
either the terms of the Eclipse Public License v1.0 as published by
the Eclipse Foundation
  or (per the licensee's choosing)
under the terms of the GNU Lesser General Public License version 2.1
as published by the Free Software Foundation.
/**
 * Logback: the reliable, generic, fast and flexible logging framework.
 * Copyright (C) 1999-2015, QOS.ch. All rights reserved.
 *
 * This program and the accompanying materials are dual-licensed under
 * either the terms of the Eclipse Public License v1.0 as published by
 * the Eclipse Foundation
 *
 *   or (per the licensee's choosing)
 *
 * under the terms of the GNU Lesser General Public License version 2.1
 * as published by the Free Software Foundation.
 */
package ch.qos.logback.core.util;

This class serves as a gateway for invocations of a "costly" operation on a critical execution path.
Author:
Ceki Gülcü/**
 * This class serves as a gateway for invocations of a "costly" operation on a critical execution path.
 *
 * @author Ceki Gülcü
 */
public class DefaultInvocationGate implements InvocationGate {

    static final int MASK_DECREASE_RIGHT_SHIFT_COUNT = 2;

    // experiments indicate that even for the most CPU intensive applications with 200 or more threads MASK
    // values in the order of 0xFFFF is appropriate
    private static final int MAX_MASK = 0xFFFF;
    static final int DEFAULT_MASK = 0xF;

    private volatile long mask = DEFAULT_MASK;
    //private volatile long lastMaskCheck = System.currentTimeMillis();

    // IMPORTANT: This field can be updated by multiple threads. It follows that
    // its values may *not* be incremented sequentially. However, we don't care
    // about the actual value of the field except that from time to time the
    // expression (invocationCounter++ & mask) == mask) should be true.
    private long invocationCounter = 0;

    // if less than thresholdForMaskIncrease milliseconds elapse between invocations of updateMaskIfNecessary()
    // method, then the mask should be increased
    private static final long MASK_INCREASE_THRESHOLD = 100;

    // if more than thresholdForMaskDecrease milliseconds elapse between invocations of updateMaskIfNecessary() method,
    // then the mask should be decreased
    private static final long MASK_DECREASE_THRESHOLD = MASK_INCREASE_THRESHOLD * 8;

    
    public DefaultInvocationGate() {
        this(MASK_INCREASE_THRESHOLD, MASK_DECREASE_THRESHOLD, System.currentTimeMillis());
    }
    
    public  DefaultInvocationGate(long minDelayThreshold, long maxDelayThreshold, long currentTime) {
        this.minDelayThreshold = minDelayThreshold;
        this.maxDelayThreshold = maxDelayThreshold; 
        this.lowerLimitForMaskMatch = currentTime + minDelayThreshold;
        this.upperLimitForNoMaskMatch = currentTime + maxDelayThreshold;
    }
    
    private long minDelayThreshold;
    private long maxDelayThreshold;

    long lowerLimitForMaskMatch;
    long upperLimitForNoMaskMatch;

    /*
     * (non-Javadoc)
     * 
     * @see ch.qos.logback.core.util.InvocationGate#skipFurtherWork()
     */
    @Override
    final public boolean isTooSoon(long currentTime) {
        boolean maskMatch = ((invocationCounter++) & mask) == mask;

        if (maskMatch) {
            if (currentTime < this.lowerLimitForMaskMatch) {
                increaseMask();
            }
            updateLimits(currentTime);
        } else {
            if (currentTime > this.upperLimitForNoMaskMatch) {
                decreaseMask();
                updateLimits(currentTime);
                return false;
            }
        }
        return !maskMatch;
    }

    private void updateLimits(long currentTime) {
        this.lowerLimitForMaskMatch = currentTime + minDelayThreshold;
        this.upperLimitForNoMaskMatch = currentTime + maxDelayThreshold;
    }


    // package private, for testing purposes only
    long getMask() {
        return mask;
    }
    
    private void increaseMask() {
        if (mask >= MAX_MASK)
            return;
        mask = (mask << 1) | 1;
    }

    private void decreaseMask() {
        mask = mask >>> MASK_DECREASE_RIGHT_SHIFT_COUNT;
    }

    public long getInvocationCounter() {
        return invocationCounter;
    }
}