[ONOS-6267] Support configurable Executors for primitives
- Support user-provided Executors in primitive builders
- Implement default per-partition per-primitive serial executor using a shared thread pool
- Implement Executor wrappers for all primitive types
Change-Id: I53acfb173a9b49a992a9a388983791d9735ed54a
diff --git a/utils/misc/src/main/java/org/onlab/util/BestEffortSerialExecutor.java b/utils/misc/src/main/java/org/onlab/util/BestEffortSerialExecutor.java
new file mode 100644
index 0000000..936a33f
--- /dev/null
+++ b/utils/misc/src/main/java/org/onlab/util/BestEffortSerialExecutor.java
@@ -0,0 +1,76 @@
+/*
+ * Copyright 2017-present Open Networking Laboratory
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.onlab.util;
+
+import java.util.LinkedList;
+import java.util.concurrent.Executor;
+
+/**
+ * Executor that executes tasks in serial on a shared thread pool, falling back to parallel execution when threads
+ * are blocked.
+ * <p>
+ * This executor attempts to execute tasks in serial as if they occur on a single thread. However, in the event tasks
+ * are blocking a thread (a thread is in the {@link Thread.State#WAITING} or {@link Thread.State#TIMED_WAITING} state)
+ * the executor will execute tasks on parallel on the underlying {@link Executor}. This is useful for ensuring blocked
+ * threads cannot block events, but mimics a single-threaded model otherwise.
+ */
+public class BestEffortSerialExecutor implements Executor {
+ private final Executor parent;
+ private final LinkedList<Runnable> tasks = new LinkedList<>();
+ private volatile Thread thread;
+
+ public BestEffortSerialExecutor(Executor parent) {
+ this.parent = parent;
+ }
+
+ private void run() {
+ synchronized (tasks) {
+ thread = Thread.currentThread();
+ }
+ for (;;) {
+ if (!runTask()) {
+ synchronized (tasks) {
+ thread = null;
+ }
+ return;
+ }
+ }
+ }
+
+ private boolean runTask() {
+ final Runnable task;
+ synchronized (tasks) {
+ task = tasks.poll();
+ if (task == null) {
+ return false;
+ }
+ }
+ task.run();
+ return true;
+ }
+
+ @Override
+ public void execute(Runnable command) {
+ synchronized (tasks) {
+ tasks.add(command);
+ if (thread == null) {
+ parent.execute(this::run);
+ } else if (thread.getState() == Thread.State.WAITING || thread.getState() == Thread.State.TIMED_WAITING) {
+ parent.execute(this::runTask);
+ }
+ }
+ }
+}