refactor: Replace use of CoroutineContext by Dispatcher

This change replaces the use of `CoroutineContext` for passing the
`SimulationDispatcher` across the different modules of OpenDC by the
lightweight `Dispatcher` interface of the OpenDC common module.

3 files changed, 296 insertions, 270 deletions

diff --git a/opendc-common/src/main/kotlin/org/opendc/common/util/Pacer.kt b/opendc-common/src/main/java/org/opendc/common/util/Pacer.java
index b6141db1..5b8d8cb0 100644
--- a/opendc-common/src/main/kotlin/org/opendc/common/util/Pacer.kt
+++ b/opendc-common/src/main/java/org/opendc/common/util/Pacer.java
@@ -20,75 +20,75 @@
  * SOFTWARE.
  */
 
-package org.opendc.common.util
+package org.opendc.common.util;
 
-import kotlinx.coroutines.Delay
-import kotlinx.coroutines.DisposableHandle
-import kotlinx.coroutines.InternalCoroutinesApi
-import java.lang.Runnable
-import java.time.InstantSource
-import kotlin.coroutines.ContinuationInterceptor
-import kotlin.coroutines.CoroutineContext
+import java.util.function.LongConsumer;
+import org.opendc.common.Dispatcher;
+import org.opendc.common.DispatcherHandle;
 
 /**
  * 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: InstantSource,
-    private val quantum: Long,
-    private val process: (Long) -> Unit
-) {
+public final class Pacer {
+    private final Dispatcher dispatcher;
+    private final long quantumMs;
+    private final LongConsumer process;
+
     /**
-     * The [Delay] instance that provides scheduled execution of [Runnable]s.
+     * The current {@link DispatcherHandle} representing the pending scheduling cycle.
      */
-    @OptIn(InternalCoroutinesApi::class)
-    private val delay =
-        requireNotNull(context[ContinuationInterceptor] as? Delay) { "Invalid CoroutineDispatcher: no delay implementation" }
+    private DispatcherHandle handle;
 
     /**
-     * The current [DisposableHandle] representing the pending scheduling cycle.
+     * 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.
      */
-    private var handle: DisposableHandle? = null
+    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 val isPending: Boolean get() = handle != null
+    public boolean isPending() {
+        return handle != null;
+    }
 
     /**
      * Enqueue a new scheduling cycle.
      */
-    public fun enqueue() {
+    public void enqueue() {
         if (handle != null) {
-            return
+            return;
         }
 
-        val quantum = quantum
-        val now = clock.millis()
+        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.
-        val timeUntilNextSlot = quantum - (now % quantum)
+        long timeUntilNextSlot = quantumMs - (now % quantumMs);
 
-        @OptIn(InternalCoroutinesApi::class)
-        handle = delay.invokeOnTimeout(timeUntilNextSlot, {
-            process(now + timeUntilNextSlot)
-            handle = null
-        }, context)
+        handle = dispatcher.scheduleCancellable(timeUntilNextSlot, () -> {
+            process.accept(now + timeUntilNextSlot);
+            handle = null;
+        });
     }
 
     /**
      * Cancel the currently pending scheduling cycle.
      */
-    public fun cancel() {
-        val handle = handle ?: return
-        this.handle = null
-        handle.dispose()
+    public void cancel() {
+        final DispatcherHandle handle = this.handle;
+        if (handle != null) {
+            this.handle = null;
+            handle.cancel();
+        }
     }
 }
diff --git a/opendc-common/src/main/java/org/opendc/common/util/TimerScheduler.java b/opendc-common/src/main/java/org/opendc/common/util/TimerScheduler.java
new file mode 100644
index 00000000..a85605e9
--- /dev/null
+++ b/opendc-common/src/main/java/org/opendc/common/util/TimerScheduler.java
@@ -0,0 +1,256 @@
+/*
+ * 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.ArrayDeque;
+import java.util.HashMap;
+import java.util.PriorityQueue;
+import org.jetbrains.annotations.NotNull;
+import org.opendc.common.Dispatcher;
+import org.opendc.common.DispatcherHandle;
+
+/**
+ * A {@link TimerScheduler} facilitates scheduled execution of future tasks.
+ */
+public final class TimerScheduler<T> {
+    private final Dispatcher dispatcher;
+
+    /**
+     * The stack of the invocations to occur in the future.
+     */
+    private final ArrayDeque<Invocation> invocations = new ArrayDeque<>();
+
+    /**
+     * A priority queue containing the tasks to be scheduled in the future.
+     */
+    private final PriorityQueue<Timer<T>> queue = new PriorityQueue<Timer<T>>();
+
+    /**
+     * A map that keeps track of the timers.
+     */
+    private final HashMap<T, Timer<T>> timers = new HashMap<>();
+
+    /**
+     * Construct a {@link TimerScheduler} instance.
+     *
+     * @param dispatcher The {@link Dispatcher} to schedule future invocations.
+     */
+    public TimerScheduler(Dispatcher dispatcher) {
+        this.dispatcher = dispatcher;
+    }
+
+    /**
+     * Start a timer that will invoke the specified [block] after [delay].
+     * <p>
+     * Each timer has a key and if a new timer with same key is started the previous is cancelled.
+     *
+     * @param key The key of the timer to start.
+     * @param delay The delay before invoking the block.
+     * @param block The block to invoke.
+     */
+    public void startSingleTimer(T key, long delay, Runnable block) {
+        startSingleTimerTo(key, dispatcher.getTimeSource().millis() + delay, block);
+    }
+
+    /**
+     * Start a timer that will invoke the specified [block] at [timestamp].
+     * <p>
+     * Each timer has a key and if a new timer with same key is started the previous is cancelled.
+     *
+     * @param key The key of the timer to start.
+     * @param timestamp The timestamp at which to invoke the block.
+     * @param block The block to invoke.
+     */
+    public void startSingleTimerTo(T key, long timestamp, Runnable block) {
+        long now = dispatcher.getTimeSource().millis();
+        final PriorityQueue<Timer<T>> queue = this.queue;
+        final ArrayDeque<Invocation> invocations = this.invocations;
+
+        if (timestamp < now) {
+            throw new IllegalArgumentException("Timestamp must be in the future");
+        }
+
+        timers.compute(key, (k, old) -> {
+            if (old != null && old.timestamp == timestamp) {
+                // Fast-path: timer for the same timestamp already exists
+                old.block = block;
+                return old;
+            } else {
+                // Slow-path: cancel old timer and replace it with new timer
+                Timer<T> timer = new Timer<T>(key, timestamp, block);
+
+                if (old != null) {
+                    old.isCancelled = true;
+                }
+                queue.add(timer);
+                trySchedule(now, invocations, timestamp);
+
+                return timer;
+            }
+        });
+    }
+
+    /**
+     * Check if a timer with a given key is active.
+     *
+     * @param key The key to check if active.
+     * @return `true` if the timer with the specified [key] is active, `false` otherwise.
+     */
+    public boolean isTimerActive(T key) {
+        return timers.containsKey(key);
+    }
+
+    /**
+     * Cancel a timer with a given key.
+     * <p>
+     * If canceling a timer that was already canceled, or key never was used to start
+     * a timer this operation will do nothing.
+     *
+     * @param key The key of the timer to cancel.
+     */
+    public void cancel(T key) {
+        final Timer<T> timer = timers.remove(key);
+
+        // Mark the timer as cancelled
+        if (timer != null) {
+            timer.isCancelled = true;
+        }
+    }
+
+    /**
+     * Cancel all timers.
+     */
+    public void cancelAll() {
+        queue.clear();
+        timers.clear();
+
+        // Cancel all pending invocations
+        for (final Invocation invocation : invocations) {
+            invocation.cancel();
+        }
+
+        invocations.clear();
+    }
+
+    /**
+     * Try to schedule an engine invocation at the specified [target].
+     *
+     * @param now The current virtual timestamp.
+     * @param target The virtual timestamp at which the engine invocation should happen.
+     * @param scheduled The queue of scheduled invocations.
+     */
+    private void trySchedule(long now, ArrayDeque<Invocation> scheduled, long target) {
+        final Invocation head = scheduled.peek();
+
+        // Only schedule a new scheduler invocation in case the target is earlier than all other pending
+        // scheduler invocations
+        if (head == null || target < head.timestamp) {
+            final DispatcherHandle handle = dispatcher.scheduleCancellable(target - now, this::doRunTimers);
+            scheduled.addFirst(new Invocation(target, handle));
+        }
+    }
+
+    /**
+     * This method is invoked when the earliest timer expires.
+     */
+    private void doRunTimers() {
+        final ArrayDeque<Invocation> invocations = this.invocations;
+        final Invocation invocation = invocations.remove();
+
+        final PriorityQueue<Timer<T>> queue = this.queue;
+        final HashMap<T, Timer<T>> timers = this.timers;
+        long now = invocation.timestamp;
+
+        while (!queue.isEmpty()) {
+            final Timer<T> timer = queue.peek();
+
+            long timestamp = timer.timestamp;
+            boolean isCancelled = timer.isCancelled;
+
+            assert timestamp >= now : "Found task in the past";
+
+            if (timestamp > now && !isCancelled) {
+                // Schedule a task for the next event to occur.
+                trySchedule(now, invocations, timestamp);
+                break;
+            }
+
+            queue.poll();
+
+            if (!isCancelled) {
+                timers.remove(timer.key);
+                timer.run();
+            }
+        }
+    }
+
+    /**
+     * A task that is scheduled to run in the future.
+     */
+    private static class Timer<T> implements Comparable<Timer<T>> {
+        final T key;
+        final long timestamp;
+        Runnable block;
+
+        /**
+         * A flag to indicate that the task has been cancelled.
+         */
+        boolean isCancelled;
+
+        /**
+         * Construct a {@link Timer} instance.
+         */
+        public Timer(T key, long timestamp, Runnable block) {
+            this.key = key;
+            this.timestamp = timestamp;
+            this.block = block;
+        }
+
+        /**
+         * Run the task.
+         */
+        void run() {
+            block.run();
+        }
+
+        @Override
+        public int compareTo(@NotNull Timer<T> other) {
+            return Long.compare(timestamp, other.timestamp);
+        }
+    }
+
+    /**
+     * A future engine invocation.
+     * <p>
+     * This class is used to keep track of the future engine invocations created using the {@link Dispatcher} instance.
+     * In case the invocation is not needed anymore, it can be cancelled via [cancel].
+     */
+    private record Invocation(long timestamp, DispatcherHandle handle) {
+        /**
+         * Cancel the engine invocation.
+         */
+        void cancel() {
+            handle.cancel();
+        }
+    }
+}
diff --git a/opendc-common/src/main/kotlin/org/opendc/common/util/TimerScheduler.kt b/opendc-common/src/main/kotlin/org/opendc/common/util/TimerScheduler.kt
deleted file mode 100644
index 864512d3..00000000
--- a/opendc-common/src/main/kotlin/org/opendc/common/util/TimerScheduler.kt
+++ /dev/null
@@ -1,230 +0,0 @@
-/*
- * 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.time.InstantSource
-import java.util.ArrayDeque
-import java.util.PriorityQueue
-import kotlin.coroutines.ContinuationInterceptor
-import kotlin.coroutines.CoroutineContext
-
-/**
- * A TimerScheduler facilitates scheduled execution of future tasks.
- *
- * @param context The [CoroutineContext] to run the tasks with.
- * @param clock The clock to keep track of the time.
- */
-public class TimerScheduler<T>(private val context: CoroutineContext, private val clock: InstantSource) {
-    /**
-     * 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 stack of the invocations to occur in the future.
-     */
-    private val invocations = ArrayDeque<Invocation>()
-
-    /**
-     * A priority queue containing the tasks to be scheduled in the future.
-     */
-    private val queue = PriorityQueue<Timer<T>>()
-
-    /**
-     * A map that keeps track of the timers.
-     */
-    private val timers = mutableMapOf<T, Timer<T>>()
-
-    /**
-     * Start a timer that will invoke the specified [block] after [delay].
-     *
-     * Each timer has a key and if a new timer with same key is started the previous is cancelled.
-     *
-     * @param key The key of the timer to start.
-     * @param delay The delay before invoking the block.
-     * @param block The block to invoke.
-     */
-    public fun startSingleTimer(key: T, delay: Long, block: () -> Unit) {
-        startSingleTimerTo(key, clock.millis() + delay, block)
-    }
-
-    /**
-     * Start a timer that will invoke the specified [block] at [timestamp].
-     *
-     * Each timer has a key and if a new timer with same key is started the previous is cancelled.
-     *
-     * @param key The key of the timer to start.
-     * @param timestamp The timestamp at which to invoke the block.
-     * @param block The block to invoke.
-     */
-    public fun startSingleTimerTo(key: T, timestamp: Long, block: () -> Unit) {
-        val now = clock.millis()
-        val queue = queue
-        val invocations = invocations
-
-        require(timestamp >= now) { "Timestamp must be in the future" }
-
-        timers.compute(key) { _, old ->
-            if (old != null && old.timestamp == timestamp) {
-                // Fast-path: timer for the same timestamp already exists
-                old.block = block
-                old
-            } else {
-                // Slow-path: cancel old timer and replace it with new timer
-                val timer = Timer(key, timestamp, block)
-
-                old?.isCancelled = true
-                queue.add(timer)
-                trySchedule(now, invocations, timestamp)
-
-                timer
-            }
-        }
-    }
-
-    /**
-     * Check if a timer with a given key is active.
-     *
-     * @param key The key to check if active.
-     * @return `true` if the timer with the specified [key] is active, `false` otherwise.
-     */
-    public fun isTimerActive(key: T): Boolean = key in timers
-
-    /**
-     * Cancel a timer with a given key.
-     *
-     * If canceling a timer that was already canceled, or key never was used to start
-     * a timer this operation will do nothing.
-     *
-     * @param key The key of the timer to cancel.
-     */
-    public fun cancel(key: T) {
-        val timer = timers.remove(key)
-
-        // Mark the timer as cancelled
-        timer?.isCancelled = true
-    }
-
-    /**
-     * Cancel all timers.
-     */
-    public fun cancelAll() {
-        queue.clear()
-        timers.clear()
-
-        // Cancel all pending invocations
-        for (invocation in invocations) {
-            invocation.cancel()
-        }
-        invocations.clear()
-    }
-
-    /**
-     * Try to schedule an engine invocation at the specified [target].
-     *
-     * @param now The current virtual timestamp.
-     * @param target The virtual timestamp at which the engine invocation should happen.
-     * @param scheduled The queue of scheduled invocations.
-     */
-    private fun trySchedule(now: Long, scheduled: ArrayDeque<Invocation>, target: Long) {
-        val head = scheduled.peek()
-
-        // Only schedule a new scheduler invocation in case the target is earlier than all other pending
-        // scheduler invocations
-        if (head == null || target < head.timestamp) {
-            @OptIn(InternalCoroutinesApi::class)
-            val handle = delay.invokeOnTimeout(target - now, ::doRunTimers, context)
-            scheduled.addFirst(Invocation(target, handle))
-        }
-    }
-
-    /**
-     * This method is invoked when the earliest timer expires.
-     */
-    private fun doRunTimers() {
-        val invocations = invocations
-        val invocation = checkNotNull(invocations.poll()) // Clear invocation from future invocation queue
-        val now = invocation.timestamp
-
-        while (queue.isNotEmpty()) {
-            val timer = queue.peek()
-
-            val timestamp = timer.timestamp
-            val isCancelled = timer.isCancelled
-
-            assert(timestamp >= now) { "Found task in the past" }
-
-            if (timestamp > now && !isCancelled) {
-                // Schedule a task for the next event to occur.
-                trySchedule(now, invocations, timestamp)
-                break
-            }
-
-            queue.poll()
-
-            if (!isCancelled) {
-                timers.remove(timer.key)
-                timer()
-            }
-        }
-    }
-
-    /**
-     * A task that is scheduled to run in the future.
-     */
-    private class Timer<T>(val key: T, val timestamp: Long, var block: () -> Unit) : Comparable<Timer<T>> {
-        /**
-         * A flag to indicate that the task has been cancelled.
-         */
-        @JvmField
-        var isCancelled: Boolean = false
-
-        /**
-         * Run the task.
-         */
-        operator fun invoke(): Unit = block()
-
-        override fun compareTo(other: Timer<T>): Int = timestamp.compareTo(other.timestamp)
-    }
-
-    /**
-     * A future engine invocation.
-     *
-     * This class is used to keep track of the future engine invocations created using the [Delay] instance. In case
-     * the invocation is not needed anymore, it can be cancelled via [cancel].
-     */
-    private class Invocation(
-        @JvmField val timestamp: Long,
-        @JvmField val handle: DisposableHandle
-    ) {
-        /**
-         * Cancel the engine invocation.
-         */
-        fun cancel() = handle.dispose()
-    }
-}