feat(common): Add common dispatcher interface

This change adds a new interface `Dispatcher` that is used throughout
OpenDC for scheduling the execution of future tasks. This replaces the
`CoroutineContext` and `Clock` that exist on many of the implementations
in OpenDC.

With this approach, we reduce the dependency on Kotlin Coroutines.

2 files changed, 96 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();
+}