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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 kotlinx.coroutines.Delay
import kotlinx.coroutines.DisposableHandle
import kotlinx.coroutines.InternalCoroutinesApi
import java.lang.Runnable
import java.time.Clock
import kotlin.coroutines.ContinuationInterceptor
import kotlin.coroutines.CoroutineContext
/**
* Helper class to pace the incoming scheduling requests.
*
* @param context The [CoroutineContext] in which the pacer runs.
* @param clock The virtual simulation clock.
* @param quantum The scheduling quantum.
* @param process The process to invoke for the incoming requests.
*/
public class Pacer(
private val context: CoroutineContext,
private val clock: Clock,
private val quantum: Long,
private val process: (Long) -> Unit
) {
/**
* The [Delay] instance that provides scheduled execution of [Runnable]s.
*/
@OptIn(InternalCoroutinesApi::class)
private val delay =
requireNotNull(context[ContinuationInterceptor] as? Delay) { "Invalid CoroutineDispatcher: no delay implementation" }
/**
* The current [DisposableHandle] representing the pending scheduling cycle.
*/
private var handle: DisposableHandle? = null
/**
* Determine whether a scheduling cycle is pending.
*/
public val isPending: Boolean get() = handle != null
/**
* Enqueue a new scheduling cycle.
*/
public fun enqueue() {
if (handle != null) {
return
}
val quantum = quantum
val now = clock.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.
val timeUntilNextSlot = quantum - (now % quantum)
@OptIn(InternalCoroutinesApi::class)
handle = delay.invokeOnTimeout(timeUntilNextSlot, {
process(now + timeUntilNextSlot)
handle = null
}, context)
}
/**
* Cancel the currently pending scheduling cycle.
*/
public fun cancel() {
val handle = handle ?: return
this.handle = null
handle.dispose()
}
}
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