merge: Increase minimum Java version to 17 (#115)

This pull request increases the minimum version of Java required by OpenDC to 17.
This new version of Java introduces several new features compared to our old minimum 
version (11), which we attempt to apply in this conversion.

## Implementation Notes :hammer_and_pick:

* Increase minimum Java version to Java 17 
* Use RandomGenerator as randomness source 
* Add common dispatcher interface 
* Add compatibility with Kotlin coroutines
* Use InstantSource as time source
* Re-implement SimulationScheduler as Dispatcher 
* Replace use of CoroutineContext by Dispatcher 

## External Dependencies :four_leaf_clover:

* Java 17

## Breaking API Changes :warning:

* The use of `CoroutineContext` and `Clock` as parameters of classes has been replaced 
  by the `Dispatcher` interface.
* The use of `Clock` has been replaced by `InstantSource` which does not carry time
   zone info.
* The use of `Random` and `SplittableRandom` as parameter type has been replaced 
   by `RandomGenerator`

5 files changed, 479 insertions, 0 deletions

diff --git a/opendc-common/src/main/java/org/opendc/common/Dispatcher.java b/opendc-common/src/main/java/org/opendc/common/Dispatcher.java
new file mode 100644
index 00000000..8c919311
--- /dev/null
+++ b/opendc-common/src/main/java/org/opendc/common/Dispatcher.java
@@ -0,0 +1,63 @@
+/*
+ * 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;
+
+import java.time.InstantSource;
+
+/**
+ * A {@link Dispatcher} is used in OpenDC to schedule the execution of future tasks over potentially multiple threads.
+ */
+public interface Dispatcher {
+    /**
+     * Return the time source of the dispatcher as an {@link InstantSource}.
+     */
+    InstantSource getTimeSource();
+
+    /**
+     * Schedule the specified {@link Runnable} to run as soon as possible.
+     *
+     * @param command The task to execute.
+     */
+    default void schedule(Runnable command) {
+        schedule(0, command);
+    }
+
+    /**
+     * Schedule the specified {@link Runnable} to run after the specified <code>delay</code>.
+     * <p>
+     * Use this method to eliminate potential allocations in case the task does not need to be cancellable.
+     *
+     * @param delayMs The time from now to the delayed execution (in milliseconds).
+     * @param command The task to execute.
+     */
+    void schedule(long delayMs, Runnable command);
+
+    /**
+     * Schedule the specified {@link Runnable} to run after the specified <code>delay</code>.
+     *
+     * @param delayMs The time from now to the delayed execution (in milliseconds).
+     * @param command The task to execute.
+     * @return A {@link DispatcherHandle} representing pending completion of the task.
+     */
+    DispatcherHandle scheduleCancellable(long delayMs, Runnable command);
+}
diff --git a/opendc-common/src/main/java/org/opendc/common/DispatcherHandle.java b/opendc-common/src/main/java/org/opendc/common/DispatcherHandle.java
new file mode 100644
index 00000000..e34e5e11
--- /dev/null
+++ b/opendc-common/src/main/java/org/opendc/common/DispatcherHandle.java
@@ -0,0 +1,33 @@
+/*
+ * 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;
+
+/**
+ * A handle returned by a {@link Dispatcher} representing a scheduled task.
+ */
+public interface DispatcherHandle {
+    /**
+     * Attempt to cancel execution of the task.
+     */
+    void cancel();
+}
diff --git a/opendc-common/src/main/java/org/opendc/common/DispatcherProvider.java b/opendc-common/src/main/java/org/opendc/common/DispatcherProvider.java
new file mode 100644
index 00000000..2717bd0f
--- /dev/null
+++ b/opendc-common/src/main/java/org/opendc/common/DispatcherProvider.java
@@ -0,0 +1,33 @@
+/*
+ * 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;
+
+/**
+ * Interface to expose the {@link Dispatcher} instance used by a class.
+ */
+public interface DispatcherProvider {
+    /**
+     * Return the {@link Dispatcher} associated with this class.
+     */
+    Dispatcher getDispatcher();
+}
diff --git a/opendc-common/src/main/java/org/opendc/common/util/Pacer.java b/opendc-common/src/main/java/org/opendc/common/util/Pacer.java
new file mode 100644
index 00000000..5b8d8cb0
--- /dev/null
+++ b/opendc-common/src/main/java/org/opendc/common/util/Pacer.java
@@ -0,0 +1,94 @@
+/*
+ * 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);
+
+        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();
+        }
+    }
+}
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();
+        }
+    }
+}