ExecutorScheduler to wrap an Executor

rxjava-core/src/main/java/rx/schedulers/ExecutorScheduler.java

@@ -0,0 +1,186 @@
+/**
+ * Copyright 2014 Netflix, Inc.
+ *
+ * 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 rx.schedulers;
+
+import java.util.concurrent.ConcurrentLinkedQueue;
+import java.util.concurrent.Executor;
+import java.util.concurrent.Future;
+import java.util.concurrent.RejectedExecutionException;
+import java.util.concurrent.ScheduledExecutorService;
+import java.util.concurrent.TimeUnit;
+import java.util.concurrent.atomic.AtomicInteger;
+import java.util.concurrent.atomic.AtomicIntegerFieldUpdater;
+import rx.Scheduler;
+import rx.Subscription;
+import rx.functions.Action0;
+import rx.plugins.RxJavaPlugins;
+import rx.subscriptions.CompositeSubscription;
+import rx.subscriptions.MultipleAssignmentSubscription;
+import rx.subscriptions.Subscriptions;
+
+/**
+ * Scheduler that wraps an Executor instance and establishes the Scheduler contract upon it.
+ * <p>
+ * Note that thread-hopping is unavoidable with this kind of Scheduler as we don't know
+ * about the underlying threading behavior of the executor.
+ */
+/* public */final class ExecutorScheduler extends Scheduler {
+    final Executor executor;
+    public ExecutorScheduler(Executor executor) {
+        this.executor = executor;
+    }
+    @Override
+    public Worker createWorker() {
+        return new ExecutorSchedulerWorker(executor);
+    }
+    /** Worker that schedules tasks on the executor indirectly through a trampoline mechanism. */
+    static final class ExecutorSchedulerWorker extends Scheduler.Worker implements Runnable {
+        final Executor executor;
+        // TODO: use a better performing structure for task tracking
+        final CompositeSubscription tasks;
+        // TODO: use MpscLinkedQueue once available
+        final ConcurrentLinkedQueue<ExecutorAction> queue; 
+        final AtomicInteger wip;
+
+        public ExecutorSchedulerWorker(Executor executor) {
+            this.executor = executor;
+            this.queue = new ConcurrentLinkedQueue<ExecutorAction>();
+            this.wip = new AtomicInteger();
+            this.tasks = new CompositeSubscription();
+        }
+
+        @Override
+        public Subscription schedule(Action0 action) {
+            if (isUnsubscribed()) {
+                return Subscriptions.empty();
+            }
+            ExecutorAction ea = new ExecutorAction(action, tasks);
+            tasks.add(ea);
+            queue.offer(ea);
+            if (wip.getAndIncrement() == 0) {
+                try {
+                    executor.execute(this);
+                } catch (RejectedExecutionException t) {
+                    // cleanup if rejected
+                    tasks.remove(ea);
+                    wip.decrementAndGet();
+                    // report the error to the plugin
+                    RxJavaPlugins.getInstance().getErrorHandler().handleError(t);
+                    // throw it to the caller
+                    throw t;
+                }
+            }
+
+            return ea;
+        }
+
+        @Override
+        public void run() {
+            do {
+                queue.poll().run();
+            } while (wip.decrementAndGet() > 0);
+        }
+
+        @Override
+        public Subscription schedule(final Action0 action, long delayTime, TimeUnit unit) {
+            if (delayTime <= 0) {
+                return schedule(action);
+            }
+            if (isUnsubscribed()) {
+                return Subscriptions.empty();
+            }
+            ScheduledExecutorService service;
+            if (executor instanceof ScheduledExecutorService) {
+                service = (ScheduledExecutorService)executor;
+            } else {
+                service = GenericScheduledExecutorService.getInstance();
+            }
+
+            final MultipleAssignmentSubscription mas = new MultipleAssignmentSubscription();
+            // tasks.add(mas); // Needs a removal without unsubscription
+
+            try {
+                Future<?> f = service.schedule(new Runnable() {
+                    @Override
+                    public void run() {
+                        if (mas.isUnsubscribed()) {
+                            return;
+                        }
+                        mas.set(schedule(action));
+                        // tasks.delete(mas); // Needs a removal without unsubscription
+                    }
+                }, delayTime, unit);
+                mas.set(Subscriptions.from(f));
+            } catch (RejectedExecutionException t) {
+                // report the rejection to plugins
+                RxJavaPlugins.getInstance().getErrorHandler().handleError(t);
+                throw t;
+            }
+
+            return mas;
+        }
+
+        @Override
+        public boolean isUnsubscribed() {
+            return tasks.isUnsubscribed();
+        }
+
+        @Override
+        public void unsubscribe() {
+            tasks.unsubscribe();
+        }
+
+    }
+    /** Runs the actual action and maintains an unsubscription state. */
+    static final class ExecutorAction implements Runnable, Subscription {
+        final Action0 actual;
+        final CompositeSubscription parent;
+        volatile int unsubscribed;
+        static final AtomicIntegerFieldUpdater<ExecutorAction> UNSUBSCRIBED_UPDATER
+                = AtomicIntegerFieldUpdater.newUpdater(ExecutorAction.class, "unsubscribed");
+
+        public ExecutorAction(Action0 actual, CompositeSubscription parent) {
+            this.actual = actual;
+            this.parent = parent;
+        }
+
+        @Override
+        public void run() {
+            if (isUnsubscribed()) {
+                return;
+            }
+            try {
+                actual.call();
+            } catch (Throwable t) {
+                RxJavaPlugins.getInstance().getErrorHandler().handleError(t);
+            } finally {
+                unsubscribe();
+            }
+        }
+        @Override
+        public boolean isUnsubscribed() {
+            return unsubscribed != 0;
+        }
+
+        @Override
+        public void unsubscribe() {
+            if (UNSUBSCRIBED_UPDATER.compareAndSet(this, 0, 1)) {
+                parent.remove(this);
+            }
+        }
+
+    }
+}

rxjava-core/src/main/java/rx/schedulers/Schedulers.java

@@ -112,4 +112,12 @@ public static Scheduler io() {
     public static TestScheduler test() {
         return new TestScheduler();
     }
+    /**
+     * Wraps the given Executor into a new Scheduler instance.
+     * @param executor the executor to wrap
+     * @return the new scheduler wrapping the executor
+     */
+    public static Scheduler newExecutor(Executor executor) {
+        return new ExecutorScheduler(executor);
+    }
 }

rxjava-core/src/test/java/rx/schedulers/ExecutorSchedulerTest.java

@@ -0,0 +1,28 @@
+/**
+ * Copyright 2014 Netflix, Inc.
+ *
+ * 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 rx.schedulers;
+
+import java.util.concurrent.Executors;
+import rx.Scheduler;
+
+public class ExecutorSchedulerTest extends AbstractSchedulerConcurrencyTests {
+
+    @Override
+    protected Scheduler getScheduler() {
+        return Schedulers.newExecutor(Executors.newFixedThreadPool(2, new NewThreadScheduler.RxThreadFactory("TestCustomPool-")));
+    }
+
+}