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/*
 * Copyright The Sett Ltd, 2005 to 2014.
 *
 * 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 com.thesett.common.throttle;

/**
 * Throttle is an interface that supplies a {@link #throttle} method, that can only be called at the rate specified in a
 * call to the {@link #setRate} method. This can be used to restict processing to run at a certain number of operations
 * per second.
 *
 * Throttle also supplies a method to check the throttle rate, without waiting. This could be used to update a user
 * interface every time an event occurs, but only up to a maximum rate. For example, as elements are added to a list, a
 * count of elements is updated for the user to see, but only up to a maximum rate of ten updates a second, as updating
 * faster than that slows the processing of element-by-element additions to the list unnecessarily.
 *
 * 

 * CRC Card Responsibilities
 * 
 Accept throttling rate in operations per second.
 * 
 Inject short pauses to fill-out processing cycles to a specified rate.
 * 
 Check against a throttle speed without waiting.
 * 
 *
 * @author Rupert Smith
 */
public interface Throttle
{
    /**
     * Specifies the throttling rate in operations per second. This must be called with with a value, the inverse of
     * which is a measurement in nano seconds, such that the number of nano seconds do not overflow a long integer. The
     * value must also be larger than zero.
     *
     * @param hertz The throttling rate in cycles per second.
     */
    void setRate(float hertz);

    /**
     * This method can only be called at the rate set by the {@link #setRate} method, if it is called faster than this
     * it will inject short pauses to restrict the call rate to that rate.
     *
     * If the thread executing this method is interrupted, it must ensure that the threads interrupt thread remains
     * set upon exit from the method. This method does not expose InterruptedException, to indicate interruption of the
     * throttle during a timed wait. It may be changed so that it does.
     *
     * @throws InterruptedException If interrupted whilst performing a blocking wait on the throttle.
     */
    void throttle() throws InterruptedException;

    /**
     * Checks but does not enforce the throttle rate. When this method is called, it checks if a length of time greater
     * than that equal to the inverse of the throttling rate has passed since it was last called and returned 
     * true
     *
     * @return true if a length of time greater than that equal to the inverse of the throttling rate has
     *         passed since this method was last called and returned true, false otherwise. The very
     *         first time this method is called on a throttle, it returns true as the base case to the above
     *         self-referential definition.
     */
    boolean checkThrottle();

    /**
     * Checks but does not enforce the throttle rate. When this method is called, it checks if a length of time greater
     * than that equal to the inverse of the throttling rate has passed since it was last called and returned 
     * true. If the length of time still to elapse to the next throttle allow point is zero or less, this method
     * will return a negative value, if there is still time to pass until the throttle allow point, this method will
     * return a positive value indicating the amount of time still to pass. A thread can wait for that period of time
     * before rechecking the throttle condition.
     *
     * @return The length of time since or still to elaps to the next throttle allow point. A negative value indicates
     *         that the throttle time has passed and a positive time indicates that there is still time to pass before
     *         it is reached. The units are in nanoseconds.
     */
    long timeToThrottleNanos();
}