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* The use of `CoroutineContext` and `Clock` as parameters of classes has been replaced 
  by the `Dispatcher` interface.
* The use of `Clock` has been replaced by `InstantSource` which does not carry time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* The use of `Random` and `SplittableRandom` as parameter type has been replaced 
   by `RandomGenerator`

4 files changed, 106 insertions, 324 deletions

diff --git a/opendc-common/src/main/kotlin/org/opendc/common/DispatcherCoroutineDispatcher.kt b/opendc-common/src/main/kotlin/org/opendc/common/DispatcherCoroutineDispatcher.kt
new file mode 100644
index 00000000..63744ef9
--- /dev/null
+++ b/opendc-common/src/main/kotlin/org/opendc/common/DispatcherCoroutineDispatcher.kt
@@ -0,0 +1,74 @@
+/*
+ * 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 kotlinx.coroutines.CancellableContinuation
+import kotlinx.coroutines.CoroutineDispatcher
+import kotlinx.coroutines.Delay
+import kotlinx.coroutines.DisposableHandle
+import kotlinx.coroutines.ExperimentalCoroutinesApi
+import kotlinx.coroutines.InternalCoroutinesApi
+import kotlin.coroutines.CoroutineContext
+
+/**
+ * A [CoroutineDispatcher] that uses a [Dispatcher] to dispatch pending co-routines.
+ *
+ * @param dispatcher The [Dispatcher] used to manage the execution of future tasks.
+ */
+@OptIn(InternalCoroutinesApi::class)
+internal class DispatcherCoroutineDispatcher(private val dispatcher: Dispatcher) : CoroutineDispatcher(), Delay, DispatcherProvider {
+    override fun dispatch(context: CoroutineContext, block: Runnable) {
+        block.run()
+    }
+
+    override fun dispatchYield(context: CoroutineContext, block: Runnable) {
+        dispatcher.schedule(block)
+    }
+
+    @OptIn(ExperimentalCoroutinesApi::class)
+    override fun scheduleResumeAfterDelay(timeMillis: Long, continuation: CancellableContinuation<Unit>) {
+        dispatcher.schedule(timeMillis, CancellableContinuationRunnable(continuation) { resumeUndispatched(Unit) })
+    }
+
+    override fun invokeOnTimeout(timeMillis: Long, block: Runnable, context: CoroutineContext): DisposableHandle {
+        val handle = dispatcher.scheduleCancellable(timeMillis, block)
+        return DisposableHandle { handle.cancel() }
+    }
+
+    override fun getDispatcher(): Dispatcher = dispatcher
+
+    override fun toString(): String {
+        return "DispatcherCoroutineDispatcher[dispatcher=$dispatcher]"
+    }
+
+    /**
+     * This class exists to allow cleanup code to avoid throwing for cancelled continuations scheduled
+     * in the future.
+     */
+    private class CancellableContinuationRunnable<T>(
+        @JvmField val continuation: CancellableContinuation<T>,
+        private val block: CancellableContinuation<T>.() -> Unit
+    ) : Runnable {
+        override fun run() = continuation.block()
+    }
+}
diff --git a/opendc-common/src/main/kotlin/org/opendc/common/Dispatchers.kt b/opendc-common/src/main/kotlin/org/opendc/common/Dispatchers.kt
new file mode 100644
index 00000000..6dcd17af
--- /dev/null
+++ b/opendc-common/src/main/kotlin/org/opendc/common/Dispatchers.kt
@@ -0,0 +1,32 @@
+/*
+ * 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 kotlinx.coroutines.CoroutineDispatcher
+
+/**
+ * Convert a [Dispatcher] to a [CoroutineDispatcher].
+ */
+public fun Dispatcher.asCoroutineDispatcher(): CoroutineDispatcher {
+    return DispatcherCoroutineDispatcher(this)
+}
diff --git a/opendc-common/src/main/kotlin/org/opendc/common/util/Pacer.kt b/opendc-common/src/main/kotlin/org/opendc/common/util/Pacer.kt
deleted file mode 100644
index edf607d2..00000000
--- a/opendc-common/src/main/kotlin/org/opendc/common/util/Pacer.kt
+++ /dev/null
@@ -1,94 +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.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()
-    }
-}
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 44d6010f..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.Clock
-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: Clock) {
-    /**
-     * 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()
-    }
-}