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/*
* Copyright (c) 2022 AtLarge Research
*
* Permission is hereby granted, free of charge, to any person obtaining a copy
* of this software and associated documentation files (the "Software"), to deal
* in the Software without restriction, including without limitation the rights
* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
* copies of the Software, and to permit persons to whom the Software is
* furnished to do so, subject to the following conditions:
*
* The above copyright notice and this permission notice shall be included in all
* copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
* SOFTWARE.
*/
package org.opendc.common.util;
import java.util.function.LongConsumer;
import org.opendc.common.Dispatcher;
import org.opendc.common.DispatcherHandle;
/**
* Helper class to pace the incoming scheduling requests.
*/
public final class Pacer {
private final Dispatcher dispatcher;
private final long quantumMs;
private final LongConsumer process;
/**
* The current {@link DispatcherHandle} representing the pending scheduling cycle.
*/
private DispatcherHandle handle;
/**
* Construct a {@link Pacer} instance.
*
* @param dispatcher The {@link Dispatcher} to schedule future invocations.
* @param quantumMs The scheduling quantum in milliseconds.
* @param process The process to invoke for the incoming requests.
*/
public Pacer(Dispatcher dispatcher, long quantumMs, LongConsumer process) {
this.dispatcher = dispatcher;
this.quantumMs = quantumMs;
this.process = process;
}
/**
* Determine whether a scheduling cycle is pending.
*/
public boolean isPending() {
return handle != null;
}
/**
* Enqueue a new scheduling cycle.
*/
public void enqueue() {
if (handle != null) {
return;
}
final Dispatcher dispatcher = this.dispatcher;
long quantumMs = this.quantumMs;
long now = dispatcher.getTimeSource().millis();
// We assume that the scheduler runs at a fixed slot every time quantum (e.g t=0, t=60, t=120).
// We calculate here the delay until the next scheduling slot.
long timeUntilNextSlot = (quantumMs - (now % quantumMs)) % quantumMs;
handle = dispatcher.scheduleCancellable(timeUntilNextSlot, () -> {
process.accept(now + timeUntilNextSlot);
handle = null;
});
}
/**
* Cancel the currently pending scheduling cycle.
*/
public void cancel() {
final DispatcherHandle handle = this.handle;
if (handle != null) {
this.handle = null;
handle.cancel();
}
}
}
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