--- /dev/null Thu Jan 01 00:00:00 1970 +0000
+++ b/jdk/src/java.base/share/classes/java/util/concurrent/Flow.java Tue Oct 13 16:25:10 2015 -0700
@@ -0,0 +1,319 @@
+/*
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation. Oracle designates this
+ * particular file as subject to the "Classpath" exception as provided
+ * by Oracle in the LICENSE file that accompanied this code.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+/*
+ * This file is available under and governed by the GNU General Public
+ * License version 2 only, as published by the Free Software Foundation.
+ * However, the following notice accompanied the original version of this
+ * file:
+ *
+ * Written by Doug Lea with assistance from members of JCP JSR-166
+ * Expert Group and released to the public domain, as explained at
+ * http://creativecommons.org/publicdomain/zero/1.0/
+ */
+
+package java.util.concurrent;
+
+/**
+ * Interrelated interfaces and static methods for establishing
+ * flow-controlled components in which {@link Publisher Publishers}
+ * produce items consumed by one or more {@link Subscriber
+ * Subscribers}, each managed by a {@link Subscription
+ * Subscription}.
+ *
+ * <p>These interfaces correspond to the <a
+ * href="http://www.reactive-streams.org/"> reactive-streams</a>
+ * specification. They apply in both concurrent and distributed
+ * asynchronous settings: All (seven) methods are defined in {@code
+ * void} "one-way" message style. Communication relies on a simple form
+ * of flow control (method {@link Subscription#request}) that can be
+ * used to avoid resource management problems that may otherwise occur
+ * in "push" based systems.
+ *
+ * <p><b>Examples.</b> A {@link Publisher} usually defines its own
+ * {@link Subscription} implementation; constructing one in method
+ * {@code subscribe} and issuing it to the calling {@link
+ * Subscriber}. It publishes items to the subscriber asynchronously,
+ * normally using an {@link Executor}. For example, here is a very
+ * simple publisher that only issues (when requested) a single {@code
+ * TRUE} item to a single subscriber. Because the subscriber receives
+ * only a single item, this class does not use buffering and ordering
+ * control required in most implementations (for example {@link
+ * SubmissionPublisher}).
+ *
+ * <pre> {@code
+ * class OneShotPublisher implements Publisher<Boolean> {
+ * private final ExecutorService executor = ForkJoinPool.commonPool(); // daemon-based
+ * private boolean subscribed; // true after first subscribe
+ * public synchronized void subscribe(Subscriber<? super Boolean> subscriber) {
+ * if (subscribed)
+ * subscriber.onError(new IllegalStateException()); // only one allowed
+ * else {
+ * subscribed = true;
+ * subscriber.onSubscribe(new OneShotSubscription(subscriber, executor));
+ * }
+ * }
+ * static class OneShotSubscription implements Subscription {
+ * private final Subscriber<? super Boolean> subscriber;
+ * private final ExecutorService executor;
+ * private Future<?> future; // to allow cancellation
+ * private boolean completed;
+ * OneShotSubscription(Subscriber<? super Boolean> subscriber,
+ * ExecutorService executor) {
+ * this.subscriber = subscriber;
+ * this.executor = executor;
+ * }
+ * public synchronized void request(long n) {
+ * if (n != 0 && !completed) {
+ * completed = true;
+ * if (n < 0) {
+ * IllegalArgumentException ex = new IllegalArgumentException();
+ * executor.execute(() -> subscriber.onError(ex));
+ * } else {
+ * future = executor.submit(() -> {
+ * subscriber.onNext(Boolean.TRUE);
+ * subscriber.onComplete();
+ * });
+ * }
+ * }
+ * }
+ * public synchronized void cancel() {
+ * completed = true;
+ * if (future != null) future.cancel(false);
+ * }
+ * }
+ * }}</pre>
+ *
+ * <p>A {@link Subscriber} arranges that items be requested and
+ * processed. Items (invocations of {@link Subscriber#onNext}) are
+ * not issued unless requested, but multiple items may be requested.
+ * Many Subscriber implementations can arrange this in the style of
+ * the following example, where a buffer size of 1 single-steps, and
+ * larger sizes usually allow for more efficient overlapped processing
+ * with less communication; for example with a value of 64, this keeps
+ * total outstanding requests between 32 and 64.
+ * Because Subscriber method invocations for a given {@link
+ * Subscription} are strictly ordered, there is no need for these
+ * methods to use locks or volatiles unless a Subscriber maintains
+ * multiple Subscriptions (in which case it is better to instead
+ * define multiple Subscribers, each with its own Subscription).
+ *
+ * <pre> {@code
+ * class SampleSubscriber<T> implements Subscriber<T> {
+ * final Consumer<? super T> consumer;
+ * Subscription subscription;
+ * final long bufferSize;
+ * long count;
+ * SampleSubscriber(long bufferSize, Consumer<? super T> consumer) {
+ * this.bufferSize = bufferSize;
+ * this.consumer = consumer;
+ * }
+ * public void onSubscribe(Subscription subscription) {
+ * long initialRequestSize = bufferSize;
+ * count = bufferSize - bufferSize / 2; // re-request when half consumed
+ * (this.subscription = subscription).request(initialRequestSize);
+ * }
+ * public void onNext(T item) {
+ * if (--count <= 0)
+ * subscription.request(count = bufferSize - bufferSize / 2);
+ * consumer.accept(item);
+ * }
+ * public void onError(Throwable ex) { ex.printStackTrace(); }
+ * public void onComplete() {}
+ * }}</pre>
+ *
+ * <p>The default value of {@link #defaultBufferSize} may provide a
+ * useful starting point for choosing request sizes and capacities in
+ * Flow components based on expected rates, resources, and usages.
+ * Or, when flow control is never needed, a subscriber may initially
+ * request an effectively unbounded number of items, as in:
+ *
+ * <pre> {@code
+ * class UnboundedSubscriber<T> implements Subscriber<T> {
+ * public void onSubscribe(Subscription subscription) {
+ * subscription.request(Long.MAX_VALUE); // effectively unbounded
+ * }
+ * public void onNext(T item) { use(item); }
+ * public void onError(Throwable ex) { ex.printStackTrace(); }
+ * public void onComplete() {}
+ * void use(T item) { ... }
+ * }}</pre>
+ *
+ * @author Doug Lea
+ * @since 1.9
+ */
+public final class Flow {
+
+ private Flow() {} // uninstantiable
+
+ /**
+ * A producer of items (and related control messages) received by
+ * Subscribers. Each current {@link Subscriber} receives the same
+ * items (via method {@code onNext}) in the same order, unless
+ * drops or errors are encountered. If a Publisher encounters an
+ * error that does not allow items to be issued to a Subscriber,
+ * that Subscriber receives {@code onError}, and then receives no
+ * further messages. Otherwise, when it is known that no further
+ * messages will be issued to it, a subscriber receives {@code
+ * onComplete}. Publishers ensure that Subscriber method
+ * invocations for each subscription are strictly ordered in <a
+ * href="package-summary.html#MemoryVisibility"><i>happens-before</i></a>
+ * order.
+ *
+ * <p>Publishers may vary in policy about whether drops (failures
+ * to issue an item because of resource limitations) are treated
+ * as unrecoverable errors. Publishers may also vary about
+ * whether Subscribers receive items that were produced or
+ * available before they subscribed.
+ *
+ * @param <T> the published item type
+ */
+ @FunctionalInterface
+ public static interface Publisher<T> {
+ /**
+ * Adds the given Subscriber if possible. If already
+ * subscribed, or the attempt to subscribe fails due to policy
+ * violations or errors, the Subscriber's {@code onError}
+ * method is invoked with an {@link IllegalStateException}.
+ * Otherwise, the Subscriber's {@code onSubscribe} method is
+ * invoked with a new {@link Subscription}. Subscribers may
+ * enable receiving items by invoking the {@code request}
+ * method of this Subscription, and may unsubscribe by
+ * invoking its {@code cancel} method.
+ *
+ * @param subscriber the subscriber
+ * @throws NullPointerException if subscriber is null
+ */
+ public void subscribe(Subscriber<? super T> subscriber);
+ }
+
+ /**
+ * A receiver of messages. The methods in this interface are
+ * invoked in strict sequential order for each {@link
+ * Subscription}.
+ *
+ * @param <T> the subscribed item type
+ */
+ public static interface Subscriber<T> {
+ /**
+ * Method invoked prior to invoking any other Subscriber
+ * methods for the given Subscription. If this method throws
+ * an exception, resulting behavior is not guaranteed, but may
+ * cause the Subscription not to be established or to be cancelled.
+ *
+ * <p>Typically, implementations of this method invoke {@code
+ * subscription.request} to enable receiving items.
+ *
+ * @param subscription a new subscription
+ */
+ public void onSubscribe(Subscription subscription);
+
+ /**
+ * Method invoked with a Subscription's next item. If this
+ * method throws an exception, resulting behavior is not
+ * guaranteed, but may cause the Subscription to be cancelled.
+ *
+ * @param item the item
+ */
+ public void onNext(T item);
+
+ /**
+ * Method invoked upon an unrecoverable error encountered by a
+ * Publisher or Subscription, after which no other Subscriber
+ * methods are invoked by the Subscription. If this method
+ * itself throws an exception, resulting behavior is
+ * undefined.
+ *
+ * @param throwable the exception
+ */
+ public void onError(Throwable throwable);
+
+ /**
+ * Method invoked when it is known that no additional
+ * Subscriber method invocations will occur for a Subscription
+ * that is not already terminated by error, after which no
+ * other Subscriber methods are invoked by the Subscription.
+ * If this method throws an exception, resulting behavior is
+ * undefined.
+ */
+ public void onComplete();
+ }
+
+ /**
+ * Message control linking a {@link Publisher} and {@link
+ * Subscriber}. Subscribers receive items only when requested,
+ * and may cancel at any time. The methods in this interface are
+ * intended to be invoked only by their Subscribers; usages in
+ * other contexts have undefined effects.
+ */
+ public static interface Subscription {
+ /**
+ * Adds the given number {@code n} of items to the current
+ * unfulfilled demand for this subscription. If {@code n} is
+ * negative, the Subscriber will receive an {@code onError}
+ * signal with an {@link IllegalArgumentException} argument.
+ * Otherwise, the Subscriber will receive up to {@code n}
+ * additional {@code onNext} invocations (or fewer if
+ * terminated).
+ *
+ * @param n the increment of demand; a value of {@code
+ * Long.MAX_VALUE} may be considered as effectively unbounded
+ */
+ public void request(long n);
+
+ /**
+ * Causes the Subscriber to (eventually) stop receiving
+ * messages. Implementation is best-effort -- additional
+ * messages may be received after invoking this method.
+ * A cancelled subscription need not ever receive an
+ * {@code onComplete} or {@code onError} signal.
+ */
+ public void cancel();
+ }
+
+ /**
+ * A component that acts as both a Subscriber and Publisher.
+ *
+ * @param <T> the subscribed item type
+ * @param <R> the published item type
+ */
+ public static interface Processor<T,R> extends Subscriber<T>, Publisher<R> {
+ }
+
+ static final int DEFAULT_BUFFER_SIZE = 256;
+
+ /**
+ * Returns a default value for Publisher or Subscriber buffering,
+ * that may be used in the absence of other constraints.
+ *
+ * @implNote
+ * The current value returned is 256.
+ *
+ * @return the buffer size value
+ */
+ public static int defaultBufferSize() {
+ return DEFAULT_BUFFER_SIZE;
+ }
+
+}
--- /dev/null Thu Jan 01 00:00:00 1970 +0000
+++ b/jdk/src/java.base/share/classes/java/util/concurrent/SubmissionPublisher.java Tue Oct 13 16:25:10 2015 -0700
@@ -0,0 +1,1632 @@
+/*
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation. Oracle designates this
+ * particular file as subject to the "Classpath" exception as provided
+ * by Oracle in the LICENSE file that accompanied this code.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+/*
+ * This file is available under and governed by the GNU General Public
+ * License version 2 only, as published by the Free Software Foundation.
+ * However, the following notice accompanied the original version of this
+ * file:
+ *
+ * Written by Doug Lea with assistance from members of JCP JSR-166
+ * Expert Group and released to the public domain, as explained at
+ * http://creativecommons.org/publicdomain/zero/1.0/
+ */
+
+package java.util.concurrent;
+
+import java.util.ArrayList;
+import java.util.List;
+import java.util.concurrent.locks.LockSupport;
+import java.util.function.BiConsumer;
+import java.util.function.BiPredicate;
+import java.util.function.Consumer;
+
+/**
+ * A {@link Flow.Publisher} that asynchronously issues submitted
+ * (non-null) items to current subscribers until it is closed. Each
+ * current subscriber receives newly submitted items in the same order
+ * unless drops or exceptions are encountered. Using a
+ * SubmissionPublisher allows item generators to act as compliant <a
+ * href="http://www.reactive-streams.org/"> reactive-streams</a>
+ * Publishers relying on drop handling and/or blocking for flow
+ * control.
+ *
+ * <p>A SubmissionPublisher uses the {@link Executor} supplied in its
+ * constructor for delivery to subscribers. The best choice of
+ * Executor depends on expected usage. If the generator(s) of
+ * submitted items run in separate threads, and the number of
+ * subscribers can be estimated, consider using a {@link
+ * Executors#newFixedThreadPool}. Otherwise consider using the
+ * default, normally the {@link ForkJoinPool#commonPool}.
+ *
+ * <p>Buffering allows producers and consumers to transiently operate
+ * at different rates. Each subscriber uses an independent buffer.
+ * Buffers are created upon first use and expanded as needed up to the
+ * given maximum. (The enforced capacity may be rounded up to the
+ * nearest power of two and/or bounded by the largest value supported
+ * by this implementation.) Invocations of {@link
+ * Flow.Subscription#request(long) request} do not directly result in
+ * buffer expansion, but risk saturation if unfilled requests exceed
+ * the maximum capacity. The default value of {@link
+ * Flow#defaultBufferSize()} may provide a useful starting point for
+ * choosing a capacity based on expected rates, resources, and usages.
+ *
+ * <p>Publication methods support different policies about what to do
+ * when buffers are saturated. Method {@link #submit(Object) submit}
+ * blocks until resources are available. This is simplest, but least
+ * responsive. The {@code offer} methods may drop items (either
+ * immediately or with bounded timeout), but provide an opportunity to
+ * interpose a handler and then retry.
+ *
+ * <p>If any Subscriber method throws an exception, its subscription
+ * is cancelled. If a handler is supplied as a constructor argument,
+ * it is invoked before cancellation upon an exception in method
+ * {@link Flow.Subscriber#onNext onNext}, but exceptions in methods
+ * {@link Flow.Subscriber#onSubscribe onSubscribe},
+ * {@link Flow.Subscriber#onError(Throwable) onError} and
+ * {@link Flow.Subscriber#onComplete() onComplete} are not recorded or
+ * handled before cancellation. If the supplied Executor throws
+ * {@link RejectedExecutionException} (or any other RuntimeException
+ * or Error) when attempting to execute a task, or a drop handler
+ * throws an exception when processing a dropped item, then the
+ * exception is rethrown. In these cases, not all subscribers will
+ * have been issued the published item. It is usually good practice to
+ * {@link #closeExceptionally closeExceptionally} in these cases.
+ *
+ * <p>Method {@link #consume(Consumer)} simplifies support for a
+ * common case in which the only action of a subscriber is to request
+ * and process all items using a supplied function.
+ *
+ * <p>This class may also serve as a convenient base for subclasses
+ * that generate items, and use the methods in this class to publish
+ * them. For example here is a class that periodically publishes the
+ * items generated from a supplier. (In practice you might add methods
+ * to independently start and stop generation, to share Executors
+ * among publishers, and so on, or use a SubmissionPublisher as a
+ * component rather than a superclass.)
+ *
+ * <pre> {@code
+ * class PeriodicPublisher<T> extends SubmissionPublisher<T> {
+ * final ScheduledFuture<?> periodicTask;
+ * final ScheduledExecutorService scheduler;
+ * PeriodicPublisher(Executor executor, int maxBufferCapacity,
+ * Supplier<? extends T> supplier,
+ * long period, TimeUnit unit) {
+ * super(executor, maxBufferCapacity);
+ * scheduler = new ScheduledThreadPoolExecutor(1);
+ * periodicTask = scheduler.scheduleAtFixedRate(
+ * () -> submit(supplier.get()), 0, period, unit);
+ * }
+ * public void close() {
+ * periodicTask.cancel(false);
+ * scheduler.shutdown();
+ * super.close();
+ * }
+ * }}</pre>
+ *
+ * <p>Here is an example of a {@link Flow.Processor} implementation.
+ * It uses single-step requests to its publisher for simplicity of
+ * illustration. A more adaptive version could monitor flow using the
+ * lag estimate returned from {@code submit}, along with other utility
+ * methods.
+ *
+ * <pre> {@code
+ * class TransformProcessor<S,T> extends SubmissionPublisher<T>
+ * implements Flow.Processor<S,T> {
+ * final Function<? super S, ? extends T> function;
+ * Flow.Subscription subscription;
+ * TransformProcessor(Executor executor, int maxBufferCapacity,
+ * Function<? super S, ? extends T> function) {
+ * super(executor, maxBufferCapacity);
+ * this.function = function;
+ * }
+ * public void onSubscribe(Flow.Subscription subscription) {
+ * (this.subscription = subscription).request(1);
+ * }
+ * public void onNext(S item) {
+ * subscription.request(1);
+ * submit(function.apply(item));
+ * }
+ * public void onError(Throwable ex) { closeExceptionally(ex); }
+ * public void onComplete() { close(); }
+ * }}</pre>
+ *
+ * @param <T> the published item type
+ * @author Doug Lea
+ * @since 1.9
+ */
+public class SubmissionPublisher<T> implements Flow.Publisher<T>,
+ AutoCloseable {
+ /*
+ * Most mechanics are handled by BufferedSubscription. This class
+ * mainly tracks subscribers and ensures sequentiality, by using
+ * built-in synchronization locks across public methods. (Using
+ * built-in locks works well in the most typical case in which
+ * only one thread submits items).
+ */
+
+ /** The largest possible power of two array size. */
+ static final int BUFFER_CAPACITY_LIMIT = 1 << 30;
+
+ /** Round capacity to power of 2, at most limit. */
+ static final int roundCapacity(int cap) {
+ int n = cap - 1;
+ n |= n >>> 1;
+ n |= n >>> 2;
+ n |= n >>> 4;
+ n |= n >>> 8;
+ n |= n >>> 16;
+ return (n <= 0) ? 1 : // at least 1
+ (n >= BUFFER_CAPACITY_LIMIT) ? BUFFER_CAPACITY_LIMIT : n + 1;
+ }
+
+ // default Executor setup; nearly the same as CompletableFuture
+
+ /**
+ * Default executor -- ForkJoinPool.commonPool() unless it cannot
+ * support parallelism.
+ */
+ private static final Executor ASYNC_POOL =
+ (ForkJoinPool.getCommonPoolParallelism() > 1) ?
+ ForkJoinPool.commonPool() : new ThreadPerTaskExecutor();
+
+ /** Fallback if ForkJoinPool.commonPool() cannot support parallelism */
+ private static final class ThreadPerTaskExecutor implements Executor {
+ public void execute(Runnable r) { new Thread(r).start(); }
+ }
+
+ /**
+ * Clients (BufferedSubscriptions) are maintained in a linked list
+ * (via their "next" fields). This works well for publish loops.
+ * It requires O(n) traversal to check for duplicate subscribers,
+ * but we expect that subscribing is much less common than
+ * publishing. Unsubscribing occurs only during traversal loops,
+ * when BufferedSubscription methods return negative values
+ * signifying that they have been disabled. To reduce
+ * head-of-line blocking, submit and offer methods first call
+ * BufferedSubscription.offer on each subscriber, and place
+ * saturated ones in retries list (using nextRetry field), and
+ * retry, possibly blocking or dropping.
+ */
+ BufferedSubscription<T> clients;
+
+ /** Run status, updated only within locks */
+ volatile boolean closed;
+ /** If non-null, the exception in closeExceptionally */
+ volatile Throwable closedException;
+
+ // Parameters for constructing BufferedSubscriptions
+ final Executor executor;
+ final BiConsumer<? super Flow.Subscriber<? super T>, ? super Throwable> onNextHandler;
+ final int maxBufferCapacity;
+
+ /**
+ * Creates a new SubmissionPublisher using the given Executor for
+ * async delivery to subscribers, with the given maximum buffer size
+ * for each subscriber, and, if non-null, the given handler invoked
+ * when any Subscriber throws an exception in method {@link
+ * Flow.Subscriber#onNext(Object) onNext}.
+ *
+ * @param executor the executor to use for async delivery,
+ * supporting creation of at least one independent thread
+ * @param maxBufferCapacity the maximum capacity for each
+ * subscriber's buffer (the enforced capacity may be rounded up to
+ * the nearest power of two and/or bounded by the largest value
+ * supported by this implementation; method {@link #getMaxBufferCapacity}
+ * returns the actual value)
+ * @param handler if non-null, procedure to invoke upon exception
+ * thrown in method {@code onNext}
+ * @throws NullPointerException if executor is null
+ * @throws IllegalArgumentException if maxBufferCapacity not
+ * positive
+ */
+ public SubmissionPublisher(Executor executor, int maxBufferCapacity,
+ BiConsumer<? super Flow.Subscriber<? super T>, ? super Throwable> handler) {
+ if (executor == null)
+ throw new NullPointerException();
+ if (maxBufferCapacity <= 0)
+ throw new IllegalArgumentException("capacity must be positive");
+ this.executor = executor;
+ this.onNextHandler = handler;
+ this.maxBufferCapacity = roundCapacity(maxBufferCapacity);
+ }
+
+ /**
+ * Creates a new SubmissionPublisher using the given Executor for
+ * async delivery to subscribers, with the given maximum buffer size
+ * for each subscriber, and no handler for Subscriber exceptions in
+ * method {@link Flow.Subscriber#onNext(Object) onNext}.
+ *
+ * @param executor the executor to use for async delivery,
+ * supporting creation of at least one independent thread
+ * @param maxBufferCapacity the maximum capacity for each
+ * subscriber's buffer (the enforced capacity may be rounded up to
+ * the nearest power of two and/or bounded by the largest value
+ * supported by this implementation; method {@link #getMaxBufferCapacity}
+ * returns the actual value)
+ * @throws NullPointerException if executor is null
+ * @throws IllegalArgumentException if maxBufferCapacity not
+ * positive
+ */
+ public SubmissionPublisher(Executor executor, int maxBufferCapacity) {
+ this(executor, maxBufferCapacity, null);
+ }
+
+ /**
+ * Creates a new SubmissionPublisher using the {@link
+ * ForkJoinPool#commonPool()} for async delivery to subscribers
+ * (unless it does not support a parallelism level of at least two,
+ * in which case, a new Thread is created to run each task), with
+ * maximum buffer capacity of {@link Flow#defaultBufferSize}, and no
+ * handler for Subscriber exceptions in method {@link
+ * Flow.Subscriber#onNext(Object) onNext}.
+ */
+ public SubmissionPublisher() {
+ this(ASYNC_POOL, Flow.defaultBufferSize(), null);
+ }
+
+ /**
+ * Adds the given Subscriber unless already subscribed. If already
+ * subscribed, the Subscriber's {@link
+ * Flow.Subscriber#onError(Throwable) onError} method is invoked on
+ * the existing subscription with an {@link IllegalStateException}.
+ * Otherwise, upon success, the Subscriber's {@link
+ * Flow.Subscriber#onSubscribe onSubscribe} method is invoked
+ * asynchronously with a new {@link Flow.Subscription}. If {@link
+ * Flow.Subscriber#onSubscribe onSubscribe} throws an exception, the
+ * subscription is cancelled. Otherwise, if this SubmissionPublisher
+ * was closed exceptionally, then the subscriber's {@link
+ * Flow.Subscriber#onError onError} method is invoked with the
+ * corresponding exception, or if closed without exception, the
+ * subscriber's {@link Flow.Subscriber#onComplete() onComplete}
+ * method is invoked. Subscribers may enable receiving items by
+ * invoking the {@link Flow.Subscription#request(long) request}
+ * method of the new Subscription, and may unsubscribe by invoking
+ * its {@link Flow.Subscription#cancel() cancel} method.
+ *
+ * @param subscriber the subscriber
+ * @throws NullPointerException if subscriber is null
+ */
+ public void subscribe(Flow.Subscriber<? super T> subscriber) {
+ if (subscriber == null) throw new NullPointerException();
+ BufferedSubscription<T> subscription =
+ new BufferedSubscription<T>(subscriber, executor,
+ onNextHandler, maxBufferCapacity);
+ synchronized (this) {
+ for (BufferedSubscription<T> b = clients, pred = null;;) {
+ if (b == null) {
+ Throwable ex;
+ subscription.onSubscribe();
+ if ((ex = closedException) != null)
+ subscription.onError(ex);
+ else if (closed)
+ subscription.onComplete();
+ else if (pred == null)
+ clients = subscription;
+ else
+ pred.next = subscription;
+ break;
+ }
+ BufferedSubscription<T> next = b.next;
+ if (b.isDisabled()) { // remove
+ b.next = null; // detach
+ if (pred == null)
+ clients = next;
+ else
+ pred.next = next;
+ }
+ else if (subscriber.equals(b.subscriber)) {
+ b.onError(new IllegalStateException("Duplicate subscribe"));
+ break;
+ }
+ else
+ pred = b;
+ b = next;
+ }
+ }
+ }
+
+ /**
+ * Publishes the given item to each current subscriber by
+ * asynchronously invoking its {@link Flow.Subscriber#onNext(Object)
+ * onNext} method, blocking uninterruptibly while resources for any
+ * subscriber are unavailable. This method returns an estimate of
+ * the maximum lag (number of items submitted but not yet consumed)
+ * among all current subscribers. This value is at least one
+ * (accounting for this submitted item) if there are any
+ * subscribers, else zero.
+ *
+ * <p>If the Executor for this publisher throws a
+ * RejectedExecutionException (or any other RuntimeException or
+ * Error) when attempting to asynchronously notify subscribers,
+ * then this exception is rethrown, in which case not all
+ * subscribers will have been issued this item.
+ *
+ * @param item the (non-null) item to publish
+ * @return the estimated maximum lag among subscribers
+ * @throws IllegalStateException if closed
+ * @throws NullPointerException if item is null
+ * @throws RejectedExecutionException if thrown by Executor
+ */
+ public int submit(T item) {
+ if (item == null) throw new NullPointerException();
+ int lag = 0;
+ boolean complete;
+ synchronized (this) {
+ complete = closed;
+ BufferedSubscription<T> b = clients;
+ if (!complete) {
+ BufferedSubscription<T> pred = null, r = null, rtail = null;
+ while (b != null) {
+ BufferedSubscription<T> next = b.next;
+ int stat = b.offer(item);
+ if (stat < 0) { // disabled
+ b.next = null;
+ if (pred == null)
+ clients = next;
+ else
+ pred.next = next;
+ }
+ else {
+ if (stat > lag)
+ lag = stat;
+ else if (stat == 0) { // place on retry list
+ b.nextRetry = null;
+ if (rtail == null)
+ r = b;
+ else
+ rtail.nextRetry = b;
+ rtail = b;
+ }
+ pred = b;
+ }
+ b = next;
+ }
+ while (r != null) {
+ BufferedSubscription<T> nextRetry = r.nextRetry;
+ r.nextRetry = null;
+ int stat = r.submit(item);
+ if (stat > lag)
+ lag = stat;
+ else if (stat < 0 && clients == r)
+ clients = r.next; // postpone internal unsubscribes
+ r = nextRetry;
+ }
+ }
+ }
+ if (complete)
+ throw new IllegalStateException("Closed");
+ else
+ return lag;
+ }
+
+ /**
+ * Publishes the given item, if possible, to each current subscriber
+ * by asynchronously invoking its {@link
+ * Flow.Subscriber#onNext(Object) onNext} method. The item may be
+ * dropped by one or more subscribers if resource limits are
+ * exceeded, in which case the given handler (if non-null) is
+ * invoked, and if it returns true, retried once. Other calls to
+ * methods in this class by other threads are blocked while the
+ * handler is invoked. Unless recovery is assured, options are
+ * usually limited to logging the error and/or issuing an {@link
+ * Flow.Subscriber#onError(Throwable) onError} signal to the
+ * subscriber.
+ *
+ * <p>This method returns a status indicator: If negative, it
+ * represents the (negative) number of drops (failed attempts to
+ * issue the item to a subscriber). Otherwise it is an estimate of
+ * the maximum lag (number of items submitted but not yet
+ * consumed) among all current subscribers. This value is at least
+ * one (accounting for this submitted item) if there are any
+ * subscribers, else zero.
+ *
+ * <p>If the Executor for this publisher throws a
+ * RejectedExecutionException (or any other RuntimeException or
+ * Error) when attempting to asynchronously notify subscribers, or
+ * the drop handler throws an exception when processing a dropped
+ * item, then this exception is rethrown.
+ *
+ * @param item the (non-null) item to publish
+ * @param onDrop if non-null, the handler invoked upon a drop to a
+ * subscriber, with arguments of the subscriber and item; if it
+ * returns true, an offer is re-attempted (once)
+ * @return if negative, the (negative) number of drops; otherwise
+ * an estimate of maximum lag
+ * @throws IllegalStateException if closed
+ * @throws NullPointerException if item is null
+ * @throws RejectedExecutionException if thrown by Executor
+ */
+ public int offer(T item,
+ BiPredicate<Flow.Subscriber<? super T>, ? super T> onDrop) {
+ return doOffer(0L, item, onDrop);
+ }
+
+ /**
+ * Publishes the given item, if possible, to each current subscriber
+ * by asynchronously invoking its {@link
+ * Flow.Subscriber#onNext(Object) onNext} method, blocking while
+ * resources for any subscription are unavailable, up to the
+ * specified timeout or until the caller thread is interrupted, at
+ * which point the given handler (if non-null) is invoked, and if it
+ * returns true, retried once. (The drop handler may distinguish
+ * timeouts from interrupts by checking whether the current thread
+ * is interrupted.) Other calls to methods in this class by other
+ * threads are blocked while the handler is invoked. Unless
+ * recovery is assured, options are usually limited to logging the
+ * error and/or issuing an {@link Flow.Subscriber#onError(Throwable)
+ * onError} signal to the subscriber.
+ *
+ * <p>This method returns a status indicator: If negative, it
+ * represents the (negative) number of drops (failed attempts to
+ * issue the item to a subscriber). Otherwise it is an estimate of
+ * the maximum lag (number of items submitted but not yet
+ * consumed) among all current subscribers. This value is at least
+ * one (accounting for this submitted item) if there are any
+ * subscribers, else zero.
+ *
+ * <p>If the Executor for this publisher throws a
+ * RejectedExecutionException (or any other RuntimeException or
+ * Error) when attempting to asynchronously notify subscribers, or
+ * the drop handler throws an exception when processing a dropped
+ * item, then this exception is rethrown.
+ *
+ * @param item the (non-null) item to publish
+ * @param timeout how long to wait for resources for any subscriber
+ * before giving up, in units of {@code unit}
+ * @param unit a {@code TimeUnit} determining how to interpret the
+ * {@code timeout} parameter
+ * @param onDrop if non-null, the handler invoked upon a drop to a
+ * subscriber, with arguments of the subscriber and item; if it
+ * returns true, an offer is re-attempted (once)
+ * @return if negative, the (negative) number of drops; otherwise
+ * an estimate of maximum lag
+ * @throws IllegalStateException if closed
+ * @throws NullPointerException if item is null
+ * @throws RejectedExecutionException if thrown by Executor
+ */
+ public int offer(T item, long timeout, TimeUnit unit,
+ BiPredicate<Flow.Subscriber<? super T>, ? super T> onDrop) {
+ return doOffer(unit.toNanos(timeout), item, onDrop);
+ }
+
+ /** Common implementation for both forms of offer */
+ final int doOffer(long nanos, T item,
+ BiPredicate<Flow.Subscriber<? super T>, ? super T> onDrop) {
+ if (item == null) throw new NullPointerException();
+ int lag = 0, drops = 0;
+ boolean complete;
+ synchronized (this) {
+ complete = closed;
+ BufferedSubscription<T> b = clients;
+ if (!complete) {
+ BufferedSubscription<T> pred = null, r = null, rtail = null;
+ while (b != null) {
+ BufferedSubscription<T> next = b.next;
+ int stat = b.offer(item);
+ if (stat < 0) {
+ b.next = null;
+ if (pred == null)
+ clients = next;
+ else
+ pred.next = next;
+ }
+ else {
+ if (stat > lag)
+ lag = stat;
+ else if (stat == 0) {
+ b.nextRetry = null;
+ if (rtail == null)
+ r = b;
+ else
+ rtail.nextRetry = b;
+ rtail = b;
+ }
+ else if (stat > lag)
+ lag = stat;
+ pred = b;
+ }
+ b = next;
+ }
+ while (r != null) {
+ BufferedSubscription<T> nextRetry = r.nextRetry;
+ r.nextRetry = null;
+ int stat = (nanos > 0L) ? r.timedOffer(item, nanos) :
+ r.offer(item);
+ if (stat == 0 && onDrop != null &&
+ onDrop.test(r.subscriber, item))
+ stat = r.offer(item);
+ if (stat == 0)
+ ++drops;
+ else if (stat > lag)
+ lag = stat;
+ else if (stat < 0 && clients == r)
+ clients = r.next;
+ r = nextRetry;
+ }
+ }
+ }
+ if (complete)
+ throw new IllegalStateException("Closed");
+ else
+ return (drops > 0) ? -drops : lag;
+ }
+
+ /**
+ * Unless already closed, issues {@link
+ * Flow.Subscriber#onComplete() onComplete} signals to current
+ * subscribers, and disallows subsequent attempts to publish.
+ * Upon return, this method does <em>NOT</em> guarantee that all
+ * subscribers have yet completed.
+ */
+ public void close() {
+ if (!closed) {
+ BufferedSubscription<T> b;
+ synchronized (this) {
+ b = clients;
+ clients = null;
+ closed = true;
+ }
+ while (b != null) {
+ BufferedSubscription<T> next = b.next;
+ b.next = null;
+ b.onComplete();
+ b = next;
+ }
+ }
+ }
+
+ /**
+ * Unless already closed, issues {@link
+ * Flow.Subscriber#onError(Throwable) onError} signals to current
+ * subscribers with the given error, and disallows subsequent
+ * attempts to publish. Future subscribers also receive the given
+ * error. Upon return, this method does <em>NOT</em> guarantee
+ * that all subscribers have yet completed.
+ *
+ * @param error the {@code onError} argument sent to subscribers
+ * @throws NullPointerException if error is null
+ */
+ public void closeExceptionally(Throwable error) {
+ if (error == null)
+ throw new NullPointerException();
+ if (!closed) {
+ BufferedSubscription<T> b;
+ synchronized (this) {
+ b = clients;
+ clients = null;
+ closed = true;
+ closedException = error;
+ }
+ while (b != null) {
+ BufferedSubscription<T> next = b.next;
+ b.next = null;
+ b.onError(error);
+ b = next;
+ }
+ }
+ }
+
+ /**
+ * Returns true if this publisher is not accepting submissions.
+ *
+ * @return true if closed
+ */
+ public boolean isClosed() {
+ return closed;
+ }
+
+ /**
+ * Returns the exception associated with {@link
+ * #closeExceptionally(Throwable) closeExceptionally}, or null if
+ * not closed or if closed normally.
+ *
+ * @return the exception, or null if none
+ */
+ public Throwable getClosedException() {
+ return closedException;
+ }
+
+ /**
+ * Returns true if this publisher has any subscribers.
+ *
+ * @return true if this publisher has any subscribers
+ */
+ public boolean hasSubscribers() {
+ boolean nonEmpty = false;
+ if (!closed) {
+ synchronized (this) {
+ for (BufferedSubscription<T> b = clients; b != null;) {
+ BufferedSubscription<T> next = b.next;
+ if (b.isDisabled()) {
+ b.next = null;
+ b = clients = next;
+ }
+ else {
+ nonEmpty = true;
+ break;
+ }
+ }
+ }
+ }
+ return nonEmpty;
+ }
+
+ /**
+ * Returns the number of current subscribers.
+ *
+ * @return the number of current subscribers
+ */
+ public int getNumberOfSubscribers() {
+ int count = 0;
+ if (!closed) {
+ synchronized (this) {
+ BufferedSubscription<T> pred = null, next;
+ for (BufferedSubscription<T> b = clients; b != null; b = next) {
+ next = b.next;
+ if (b.isDisabled()) {
+ b.next = null;
+ if (pred == null)
+ clients = next;
+ else
+ pred.next = next;
+ }
+ else {
+ pred = b;
+ ++count;
+ }
+ }
+ }
+ }
+ return count;
+ }
+
+ /**
+ * Returns the Executor used for asynchronous delivery.
+ *
+ * @return the Executor used for asynchronous delivery
+ */
+ public Executor getExecutor() {
+ return executor;
+ }
+
+ /**
+ * Returns the maximum per-subscriber buffer capacity.
+ *
+ * @return the maximum per-subscriber buffer capacity
+ */
+ public int getMaxBufferCapacity() {
+ return maxBufferCapacity;
+ }
+
+ /**
+ * Returns a list of current subscribers for monitoring and
+ * tracking purposes, not for invoking {@link Flow.Subscriber}
+ * methods on the subscribers.
+ *
+ * @return list of current subscribers
+ */
+ public List<Flow.Subscriber<? super T>> getSubscribers() {
+ ArrayList<Flow.Subscriber<? super T>> subs = new ArrayList<>();
+ synchronized (this) {
+ BufferedSubscription<T> pred = null, next;
+ for (BufferedSubscription<T> b = clients; b != null; b = next) {
+ next = b.next;
+ if (b.isDisabled()) {
+ b.next = null;
+ if (pred == null)
+ clients = next;
+ else
+ pred.next = next;
+ }
+ else
+ subs.add(b.subscriber);
+ }
+ }
+ return subs;
+ }
+
+ /**
+ * Returns true if the given Subscriber is currently subscribed.
+ *
+ * @param subscriber the subscriber
+ * @return true if currently subscribed
+ * @throws NullPointerException if subscriber is null
+ */
+ public boolean isSubscribed(Flow.Subscriber<? super T> subscriber) {
+ if (subscriber == null) throw new NullPointerException();
+ if (!closed) {
+ synchronized (this) {
+ BufferedSubscription<T> pred = null, next;
+ for (BufferedSubscription<T> b = clients; b != null; b = next) {
+ next = b.next;
+ if (b.isDisabled()) {
+ b.next = null;
+ if (pred == null)
+ clients = next;
+ else
+ pred.next = next;
+ }
+ else if (subscriber.equals(b.subscriber))
+ return true;
+ else
+ pred = b;
+ }
+ }
+ }
+ return false;
+ }
+
+ /**
+ * Returns an estimate of the minimum number of items requested
+ * (via {@link Flow.Subscription#request(long) request}) but not
+ * yet produced, among all current subscribers.
+ *
+ * @return the estimate, or zero if no subscribers
+ */
+ public long estimateMinimumDemand() {
+ long min = Long.MAX_VALUE;
+ boolean nonEmpty = false;
+ synchronized (this) {
+ BufferedSubscription<T> pred = null, next;
+ for (BufferedSubscription<T> b = clients; b != null; b = next) {
+ int n; long d;
+ next = b.next;
+ if ((n = b.estimateLag()) < 0) {
+ b.next = null;
+ if (pred == null)
+ clients = next;
+ else
+ pred.next = next;
+ }
+ else {
+ if ((d = b.demand - n) < min)
+ min = d;
+ nonEmpty = true;
+ pred = b;
+ }
+ }
+ }
+ return nonEmpty ? min : 0;
+ }
+
+ /**
+ * Returns an estimate of the maximum number of items produced but
+ * not yet consumed among all current subscribers.
+ *
+ * @return the estimate
+ */
+ public int estimateMaximumLag() {
+ int max = 0;
+ synchronized (this) {
+ BufferedSubscription<T> pred = null, next;
+ for (BufferedSubscription<T> b = clients; b != null; b = next) {
+ int n;
+ next = b.next;
+ if ((n = b.estimateLag()) < 0) {
+ b.next = null;
+ if (pred == null)
+ clients = next;
+ else
+ pred.next = next;
+ }
+ else {
+ if (n > max)
+ max = n;
+ pred = b;
+ }
+ }
+ }
+ return max;
+ }
+
+ /**
+ * Processes all published items using the given Consumer function.
+ * Returns a CompletableFuture that is completed normally when this
+ * publisher signals {@link Flow.Subscriber#onComplete()
+ * onComplete}, or completed exceptionally upon any error, or an
+ * exception is thrown by the Consumer, or the returned
+ * CompletableFuture is cancelled, in which case no further items
+ * are processed.
+ *
+ * @param consumer the function applied to each onNext item
+ * @return a CompletableFuture that is completed normally
+ * when the publisher signals onComplete, and exceptionally
+ * upon any error or cancellation
+ * @throws NullPointerException if consumer is null
+ */
+ public CompletableFuture<Void> consume(Consumer<? super T> consumer) {
+ if (consumer == null)
+ throw new NullPointerException();
+ CompletableFuture<Void> status = new CompletableFuture<>();
+ subscribe(new ConsumerSubscriber<T>(status, consumer));
+ return status;
+ }
+
+ /** Subscriber for method consume */
+ private static final class ConsumerSubscriber<T>
+ implements Flow.Subscriber<T> {
+ final CompletableFuture<Void> status;
+ final Consumer<? super T> consumer;
+ Flow.Subscription subscription;
+ ConsumerSubscriber(CompletableFuture<Void> status,
+ Consumer<? super T> consumer) {
+ this.status = status; this.consumer = consumer;
+ }
+ public final void onSubscribe(Flow.Subscription subscription) {
+ this.subscription = subscription;
+ status.whenComplete((v, e) -> subscription.cancel());
+ if (!status.isDone())
+ subscription.request(Long.MAX_VALUE);
+ }
+ public final void onError(Throwable ex) {
+ status.completeExceptionally(ex);
+ }
+ public final void onComplete() {
+ status.complete(null);
+ }
+ public final void onNext(T item) {
+ try {
+ consumer.accept(item);
+ } catch (Throwable ex) {
+ subscription.cancel();
+ status.completeExceptionally(ex);
+ }
+ }
+ }
+
+ /**
+ * A task for consuming buffer items and signals, created and
+ * executed whenever they become available. A task consumes as
+ * many items/signals as possible before terminating, at which
+ * point another task is created when needed. The dual Runnable
+ * and ForkJoinTask declaration saves overhead when executed by
+ * ForkJoinPools, without impacting other kinds of Executors.
+ */
+ @SuppressWarnings("serial")
+ static final class ConsumerTask<T> extends ForkJoinTask<Void>
+ implements Runnable {
+ final BufferedSubscription<T> consumer;
+ ConsumerTask(BufferedSubscription<T> consumer) {
+ this.consumer = consumer;
+ }
+ public final Void getRawResult() { return null; }
+ public final void setRawResult(Void v) {}
+ public final boolean exec() { consumer.consume(); return false; }
+ public final void run() { consumer.consume(); }
+ }
+
+ /**
+ * A bounded (ring) buffer with integrated control to start a
+ * consumer task whenever items are available. The buffer
+ * algorithm is similar to one used inside ForkJoinPool (see its
+ * internal documentation for details) specialized for the case of
+ * at most one concurrent producer and consumer, and power of two
+ * buffer sizes. This allows methods to operate without locks even
+ * while supporting resizing, blocking, task-triggering, and
+ * garbage-free buffers (nulling out elements when consumed),
+ * although supporting these does impose a bit of overhead
+ * compared to plain fixed-size ring buffers.
+ *
+ * The publisher guarantees a single producer via its lock. We
+ * ensure in this class that there is at most one consumer. The
+ * request and cancel methods must be fully thread-safe but are
+ * coded to exploit the most common case in which they are only
+ * called by consumers (usually within onNext).
+ *
+ * Execution control is managed using the ACTIVE ctl bit. We
+ * ensure that a task is active when consumable items (and
+ * usually, SUBSCRIBE, ERROR or COMPLETE signals) are present and
+ * there is demand (unfilled requests). This is complicated on
+ * the creation side by the possibility of exceptions when trying
+ * to execute tasks. These eventually force DISABLED state, but
+ * sometimes not directly. On the task side, termination (clearing
+ * ACTIVE) that would otherwise race with producers or request()
+ * calls uses the CONSUME keep-alive bit to force a recheck.
+ *
+ * The ctl field also manages run state. When DISABLED, no further
+ * updates are possible. Disabling may be preceded by setting
+ * ERROR or COMPLETE (or both -- ERROR has precedence), in which
+ * case the associated Subscriber methods are invoked, possibly
+ * synchronously if there is no active consumer task (including
+ * cases where execute() failed). The cancel() method is supported
+ * by treating as ERROR but suppressing onError signal.
+ *
+ * Support for blocking also exploits the fact that there is only
+ * one possible waiter. ManagedBlocker-compatible control fields
+ * are placed in this class itself rather than in wait-nodes.
+ * Blocking control relies on the "waiter" field. Producers set
+ * the field before trying to block, but must then recheck (via
+ * offer) before parking. Signalling then just unparks and clears
+ * waiter field. If the producer and consumer are both in the same
+ * ForkJoinPool, or consumers are running in commonPool, the
+ * producer attempts to help run consumer tasks that it forked
+ * before blocking. To avoid potential cycles, only one level of
+ * helping is currently supported.
+ *
+ * This class uses @Contended and heuristic field declaration
+ * ordering to reduce false-sharing-based memory contention among
+ * instances of BufferedSubscription, but it does not currently
+ * attempt to avoid memory contention among buffers. This field
+ * and element packing can hurt performance especially when each
+ * publisher has only one client operating at a high rate.
+ * Addressing this may require allocating substantially more space
+ * than users expect.
+ */
+ @SuppressWarnings("serial")
+ @sun.misc.Contended
+ private static final class BufferedSubscription<T>
+ implements Flow.Subscription, ForkJoinPool.ManagedBlocker {
+ // Order-sensitive field declarations
+ long timeout; // > 0 if timed wait
+ volatile long demand; // # unfilled requests
+ int maxCapacity; // reduced on OOME
+ int putStat; // offer result for ManagedBlocker
+ int helpDepth; // nested helping depth (at most 1)
+ volatile int ctl; // atomic run state flags
+ volatile int head; // next position to take
+ int tail; // next position to put
+ Object[] array; // buffer: null if disabled
+ Flow.Subscriber<? super T> subscriber; // null if disabled
+ Executor executor; // null if disabled
+ BiConsumer<? super Flow.Subscriber<? super T>, ? super Throwable> onNextHandler;
+ volatile Throwable pendingError; // holds until onError issued
+ volatile Thread waiter; // blocked producer thread
+ T putItem; // for offer within ManagedBlocker
+ BufferedSubscription<T> next; // used only by publisher
+ BufferedSubscription<T> nextRetry; // used only by publisher
+
+ // ctl values
+ static final int ACTIVE = 0x01; // consumer task active
+ static final int CONSUME = 0x02; // keep-alive for consumer task
+ static final int DISABLED = 0x04; // final state
+ static final int ERROR = 0x08; // signal onError then disable
+ static final int SUBSCRIBE = 0x10; // signal onSubscribe
+ static final int COMPLETE = 0x20; // signal onComplete when done
+
+ static final long INTERRUPTED = -1L; // timeout vs interrupt sentinel
+
+ /**
+ * Initial buffer capacity used when maxBufferCapacity is
+ * greater. Must be a power of two.
+ */
+ static final int DEFAULT_INITIAL_CAP = 32;
+
+ BufferedSubscription(Flow.Subscriber<? super T> subscriber,
+ Executor executor,
+ BiConsumer<? super Flow.Subscriber<? super T>,
+ ? super Throwable> onNextHandler,
+ int maxBufferCapacity) {
+ this.subscriber = subscriber;
+ this.executor = executor;
+ this.onNextHandler = onNextHandler;
+ this.maxCapacity = maxBufferCapacity;
+ this.array = new Object[maxBufferCapacity < DEFAULT_INITIAL_CAP ?
+ (maxBufferCapacity < 2 ? // at least 2 slots
+ 2 : maxBufferCapacity) :
+ DEFAULT_INITIAL_CAP];
+ }
+
+ final boolean isDisabled() {
+ return ctl == DISABLED;
+ }
+
+ /**
+ * Returns estimated number of buffered items, or -1 if
+ * disabled.
+ */
+ final int estimateLag() {
+ int n;
+ return (ctl == DISABLED) ? -1 : ((n = tail - head) > 0) ? n : 0;
+ }
+
+ /**
+ * Tries to add item and start consumer task if necessary.
+ * @return -1 if disabled, 0 if dropped, else estimated lag
+ */
+ final int offer(T item) {
+ int h = head, t = tail, cap, size, stat;
+ Object[] a = array;
+ if (a != null && (cap = a.length) > 0 && cap >= (size = t + 1 - h)) {
+ a[(cap - 1) & t] = item; // relaxed writes OK
+ tail = t + 1;
+ stat = size;
+ }
+ else
+ stat = growAndAdd(a, item);
+ return (stat > 0 &&
+ (ctl & (ACTIVE | CONSUME)) != (ACTIVE | CONSUME)) ?
+ startOnOffer(stat) : stat;
+ }
+
+ /**
+ * Tries to create or expand buffer, then adds item if possible.
+ */
+ private int growAndAdd(Object[] a, T item) {
+ boolean alloc;
+ int cap, stat;
+ if ((ctl & (ERROR | DISABLED)) != 0) {
+ cap = 0;
+ stat = -1;
+ alloc = false;
+ }
+ else if (a == null || (cap = a.length) <= 0) {
+ cap = 0;
+ stat = 1;
+ alloc = true;
+ }
+ else {
+ U.fullFence(); // recheck
+ int h = head, t = tail, size = t + 1 - h;
+ if (cap >= size) {
+ a[(cap - 1) & t] = item;
+ tail = t + 1;
+ stat = size;
+ alloc = false;
+ }
+ else if (cap >= maxCapacity) {
+ stat = 0; // cannot grow
+ alloc = false;
+ }
+ else {
+ stat = cap + 1;
+ alloc = true;
+ }
+ }
+ if (alloc) {
+ int newCap = (cap > 0) ? cap << 1 : 1;
+ if (newCap <= cap)
+ stat = 0;
+ else {
+ Object[] newArray = null;
+ try {
+ newArray = new Object[newCap];
+ } catch (Throwable ex) { // try to cope with OOME
+ }
+ if (newArray == null) {
+ if (cap > 0)
+ maxCapacity = cap; // avoid continuous failure
+ stat = 0;
+ }
+ else {
+ array = newArray;
+ int t = tail;
+ int newMask = newCap - 1;
+ if (a != null && cap > 0) {
+ int mask = cap - 1;
+ for (int j = head; j != t; ++j) {
+ long k = ((long)(j & mask) << ASHIFT) + ABASE;
+ Object x = U.getObjectVolatile(a, k);
+ if (x != null && // races with consumer
+ U.compareAndSwapObject(a, k, x, null))
+ newArray[j & newMask] = x;
+ }
+ }
+ newArray[t & newMask] = item;
+ tail = t + 1;
+ }
+ }
+ }
+ return stat;
+ }
+
+ /**
+ * Spins/helps/blocks while offer returns 0. Called only if
+ * initial offer return 0.
+ */
+ final int submit(T item) {
+ int stat; Executor e; ForkJoinWorkerThread w;
+ if ((stat = offer(item)) == 0 && helpDepth == 0 &&
+ ((e = executor) instanceof ForkJoinPool)) {
+ helpDepth = 1;
+ Thread thread = Thread.currentThread();
+ if ((thread instanceof ForkJoinWorkerThread) &&
+ ((w = (ForkJoinWorkerThread)thread)).getPool() == e)
+ stat = internalHelpConsume(w.workQueue, item);
+ else if (e == ForkJoinPool.commonPool())
+ stat = externalHelpConsume
+ (ForkJoinPool.commonSubmitterQueue(), item);
+ helpDepth = 0;
+ }
+ if (stat == 0 && (stat = offer(item)) == 0) {
+ putItem = item;
+ timeout = 0L;
+ try {
+ ForkJoinPool.managedBlock(this);
+ } catch (InterruptedException ie) {
+ timeout = INTERRUPTED;
+ }
+ stat = putStat;
+ if (timeout < 0L)
+ Thread.currentThread().interrupt();
+ }
+ return stat;
+ }
+
+ /**
+ * Tries helping for FJ submitter.
+ */
+ private int internalHelpConsume(ForkJoinPool.WorkQueue w, T item) {
+ int stat = 0;
+ if (w != null) {
+ ForkJoinTask<?> t;
+ while ((t = w.peek()) != null && (t instanceof ConsumerTask)) {
+ if ((stat = offer(item)) != 0 || !w.tryUnpush(t))
+ break;
+ ((ConsumerTask<?>)t).consumer.consume();
+ }
+ }
+ return stat;
+ }
+
+ /**
+ * Tries helping for non-FJ submitter.
+ */
+ private int externalHelpConsume(ForkJoinPool.WorkQueue w, T item) {
+ int stat = 0;
+ if (w != null) {
+ ForkJoinTask<?> t;
+ while ((t = w.peek()) != null && (t instanceof ConsumerTask)) {
+ if ((stat = offer(item)) != 0 || !w.trySharedUnpush(t))
+ break;
+ ((ConsumerTask<?>)t).consumer.consume();
+ }
+ }
+ return stat;
+ }
+
+ /**
+ * Timeout version; similar to submit.
+ */
+ final int timedOffer(T item, long nanos) {
+ int stat; Executor e;
+ if ((stat = offer(item)) == 0 && helpDepth == 0 &&
+ ((e = executor) instanceof ForkJoinPool)) {
+ Thread thread = Thread.currentThread();
+ if (((thread instanceof ForkJoinWorkerThread) &&
+ ((ForkJoinWorkerThread)thread).getPool() == e) ||
+ e == ForkJoinPool.commonPool()) {
+ helpDepth = 1;
+ ForkJoinTask<?> t;
+ long deadline = System.nanoTime() + nanos;
+ while ((t = ForkJoinTask.peekNextLocalTask()) != null &&
+ (t instanceof ConsumerTask)) {
+ if ((stat = offer(item)) != 0 ||
+ (nanos = deadline - System.nanoTime()) <= 0L ||
+ !t.tryUnfork())
+ break;
+ ((ConsumerTask<?>)t).consumer.consume();
+ }
+ helpDepth = 0;
+ }
+ }
+ if (stat == 0 && (stat = offer(item)) == 0 &&
+ (timeout = nanos) > 0L) {
+ putItem = item;
+ try {
+ ForkJoinPool.managedBlock(this);
+ } catch (InterruptedException ie) {
+ timeout = INTERRUPTED;
+ }
+ stat = putStat;
+ if (timeout < 0L)
+ Thread.currentThread().interrupt();
+ }
+ return stat;
+ }
+
+ /**
+ * Tries to start consumer task after offer.
+ * @return -1 if now disabled, else argument
+ */
+ private int startOnOffer(int stat) {
+ for (;;) {
+ Executor e; int c;
+ if ((c = ctl) == DISABLED || (e = executor) == null) {
+ stat = -1;
+ break;
+ }
+ else if ((c & ACTIVE) != 0) { // ensure keep-alive
+ if ((c & CONSUME) != 0 ||
+ U.compareAndSwapInt(this, CTL, c,
+ c | CONSUME))
+ break;
+ }
+ else if (demand == 0L || tail == head)
+ break;
+ else if (U.compareAndSwapInt(this, CTL, c,
+ c | (ACTIVE | CONSUME))) {
+ try {
+ e.execute(new ConsumerTask<T>(this));
+ break;
+ } catch (RuntimeException | Error ex) { // back out
+ do {} while (((c = ctl) & DISABLED) == 0 &&
+ (c & ACTIVE) != 0 &&
+ !U.compareAndSwapInt(this, CTL, c,
+ c & ~ACTIVE));
+ throw ex;
+ }
+ }
+ }
+ return stat;
+ }
+
+ private void signalWaiter(Thread w) {
+ waiter = null;
+ LockSupport.unpark(w); // release producer
+ }
+
+ /**
+ * Nulls out most fields, mainly to avoid garbage retention
+ * until publisher unsubscribes, but also to help cleanly stop
+ * upon error by nulling required components.
+ */
+ private void detach() {
+ Thread w = waiter;
+ executor = null;
+ subscriber = null;
+ pendingError = null;
+ signalWaiter(w);
+ }
+
+ /**
+ * Issues error signal, asynchronously if a task is running,
+ * else synchronously.
+ */
+ final void onError(Throwable ex) {
+ for (int c;;) {
+ if (((c = ctl) & (ERROR | DISABLED)) != 0)
+ break;
+ else if ((c & ACTIVE) != 0) {
+ pendingError = ex;
+ if (U.compareAndSwapInt(this, CTL, c, c | ERROR))
+ break; // cause consumer task to exit
+ }
+ else if (U.compareAndSwapInt(this, CTL, c, DISABLED)) {
+ Flow.Subscriber<? super T> s = subscriber;
+ if (s != null && ex != null) {
+ try {
+ s.onError(ex);
+ } catch (Throwable ignore) {
+ }
+ }
+ detach();
+ break;
+ }
+ }
+ }
+
+ /**
+ * Tries to start consumer task upon a signal or request;
+ * disables on failure.
+ */
+ private void startOrDisable() {
+ Executor e;
+ if ((e = executor) != null) { // skip if already disabled
+ try {
+ e.execute(new ConsumerTask<T>(this));
+ } catch (Throwable ex) { // back out and force signal
+ for (int c;;) {
+ if ((c = ctl) == DISABLED || (c & ACTIVE) == 0)
+ break;
+ if (U.compareAndSwapInt(this, CTL, c, c & ~ACTIVE)) {
+ onError(ex);
+ break;
+ }
+ }
+ }
+ }
+ }
+
+ final void onComplete() {
+ for (int c;;) {
+ if ((c = ctl) == DISABLED)
+ break;
+ if (U.compareAndSwapInt(this, CTL, c,
+ c | (ACTIVE | CONSUME | COMPLETE))) {
+ if ((c & ACTIVE) == 0)
+ startOrDisable();
+ break;
+ }
+ }
+ }
+
+ final void onSubscribe() {
+ for (int c;;) {
+ if ((c = ctl) == DISABLED)
+ break;
+ if (U.compareAndSwapInt(this, CTL, c,
+ c | (ACTIVE | CONSUME | SUBSCRIBE))) {
+ if ((c & ACTIVE) == 0)
+ startOrDisable();
+ break;
+ }
+ }
+ }
+
+ /**
+ * Causes consumer task to exit if active (without reporting
+ * onError unless there is already a pending error), and
+ * disables.
+ */
+ public void cancel() {
+ for (int c;;) {
+ if ((c = ctl) == DISABLED)
+ break;
+ else if ((c & ACTIVE) != 0) {
+ if (U.compareAndSwapInt(this, CTL, c,
+ c | (CONSUME | ERROR)))
+ break;
+ }
+ else if (U.compareAndSwapInt(this, CTL, c, DISABLED)) {
+ detach();
+ break;
+ }
+ }
+ }
+
+ /**
+ * Adds to demand and possibly starts task.
+ */
+ public void request(long n) {
+ if (n > 0L) {
+ for (;;) {
+ long prev = demand, d;
+ if ((d = prev + n) < prev) // saturate
+ d = Long.MAX_VALUE;
+ if (U.compareAndSwapLong(this, DEMAND, prev, d)) {
+ for (int c, h;;) {
+ if ((c = ctl) == DISABLED)
+ break;
+ else if ((c & ACTIVE) != 0) {
+ if ((c & CONSUME) != 0 ||
+ U.compareAndSwapInt(this, CTL, c,
+ c | CONSUME))
+ break;
+ }
+ else if ((h = head) != tail) {
+ if (U.compareAndSwapInt(this, CTL, c,
+ c | (ACTIVE|CONSUME))) {
+ startOrDisable();
+ break;
+ }
+ }
+ else if (head == h && tail == h)
+ break; // else stale
+ if (demand == 0L)
+ break;
+ }
+ break;
+ }
+ }
+ }
+ else if (n < 0L)
+ onError(new IllegalArgumentException(
+ "negative subscription request"));
+ }
+
+ public final boolean isReleasable() { // for ManagedBlocker
+ T item = putItem;
+ if (item != null) {
+ if ((putStat = offer(item)) == 0)
+ return false;
+ putItem = null;
+ }
+ return true;
+ }
+
+ public final boolean block() { // for ManagedBlocker
+ T item = putItem;
+ if (item != null) {
+ putItem = null;
+ long nanos = timeout;
+ long deadline = (nanos > 0L) ? System.nanoTime() + nanos : 0L;
+ while ((putStat = offer(item)) == 0) {
+ if (Thread.interrupted()) {
+ timeout = INTERRUPTED;
+ if (nanos > 0L)
+ break;
+ }
+ else if (nanos > 0L &&
+ (nanos = deadline - System.nanoTime()) <= 0L)
+ break;
+ else if (waiter == null)
+ waiter = Thread.currentThread();
+ else {
+ if (nanos > 0L)
+ LockSupport.parkNanos(this, nanos);
+ else
+ LockSupport.park(this);
+ waiter = null;
+ }
+ }
+ }
+ waiter = null;
+ return true;
+ }
+
+ /**
+ * Consumer loop, called from ConsumerTask, or indirectly
+ * when helping during submit.
+ */
+ final void consume() {
+ Flow.Subscriber<? super T> s;
+ int h = head;
+ if ((s = subscriber) != null) { // else disabled
+ for (;;) {
+ long d = demand;
+ int c; Object[] a; int n; long i; Object x; Thread w;
+ if (((c = ctl) & (ERROR | SUBSCRIBE | DISABLED)) != 0) {
+ if (!checkControl(s, c))
+ break;
+ }
+ else if ((a = array) == null || h == tail ||
+ (n = a.length) == 0 ||
+ (x = U.getObjectVolatile
+ (a, (i = ((long)((n - 1) & h) << ASHIFT) + ABASE)))
+ == null) {
+ if (!checkEmpty(s, c))
+ break;
+ }
+ else if (d == 0L) {
+ if (!checkDemand(c))
+ break;
+ }
+ else if (((c & CONSUME) != 0 ||
+ U.compareAndSwapInt(this, CTL, c, c | CONSUME)) &&
+ U.compareAndSwapObject(a, i, x, null)) {
+ U.putOrderedInt(this, HEAD, ++h);
+ U.getAndAddLong(this, DEMAND, -1L);
+ if ((w = waiter) != null)
+ signalWaiter(w);
+ try {
+ @SuppressWarnings("unchecked") T y = (T) x;
+ s.onNext(y);
+ } catch (Throwable ex) {
+ handleOnNext(s, ex);
+ }
+ }
+ }
+ }
+ }
+
+ /**
+ * Responds to control events in consume().
+ */
+ private boolean checkControl(Flow.Subscriber<? super T> s, int c) {
+ boolean stat = true;
+ if ((c & ERROR) != 0) {
+ Throwable ex = pendingError;
+ ctl = DISABLED; // no need for CAS
+ if (ex != null) { // null if errorless cancel
+ try {
+ if (s != null)
+ s.onError(ex);
+ } catch (Throwable ignore) {
+ }
+ }
+ }
+ else if ((c & SUBSCRIBE) != 0) {
+ if (U.compareAndSwapInt(this, CTL, c, c & ~SUBSCRIBE)) {
+ try {
+ if (s != null)
+ s.onSubscribe(this);
+ } catch (Throwable ex) {
+ onError(ex);
+ }
+ }
+ }
+ else {
+ detach();
+ stat = false;
+ }
+ return stat;
+ }
+
+ /**
+ * Responds to apparent emptiness in consume().
+ */
+ private boolean checkEmpty(Flow.Subscriber<? super T> s, int c) {
+ boolean stat = true;
+ if (head == tail) {
+ if ((c & CONSUME) != 0)
+ U.compareAndSwapInt(this, CTL, c, c & ~CONSUME);
+ else if ((c & COMPLETE) != 0) {
+ if (U.compareAndSwapInt(this, CTL, c, DISABLED)) {
+ try {
+ if (s != null)
+ s.onComplete();
+ } catch (Throwable ignore) {
+ }
+ }
+ }
+ else if (U.compareAndSwapInt(this, CTL, c, c & ~ACTIVE))
+ stat = false;
+ }
+ return stat;
+ }
+
+ /**
+ * Responds to apparent zero demand in consume().
+ */
+ private boolean checkDemand(int c) {
+ boolean stat = true;
+ if (demand == 0L) {
+ if ((c & CONSUME) != 0)
+ U.compareAndSwapInt(this, CTL, c, c & ~CONSUME);
+ else if (U.compareAndSwapInt(this, CTL, c, c & ~ACTIVE))
+ stat = false;
+ }
+ return stat;
+ }
+
+ /**
+ * Processes exception in Subscriber.onNext.
+ */
+ private void handleOnNext(Flow.Subscriber<? super T> s, Throwable ex) {
+ BiConsumer<? super Flow.Subscriber<? super T>, ? super Throwable> h;
+ if ((h = onNextHandler) != null) {
+ try {
+ h.accept(s, ex);
+ } catch (Throwable ignore) {
+ }
+ }
+ onError(ex);
+ }
+
+ // Unsafe mechanics
+ private static final sun.misc.Unsafe U = sun.misc.Unsafe.getUnsafe();
+ private static final long CTL;
+ private static final long TAIL;
+ private static final long HEAD;
+ private static final long DEMAND;
+ private static final int ABASE;
+ private static final int ASHIFT;
+
+ static {
+ try {
+ CTL = U.objectFieldOffset
+ (BufferedSubscription.class.getDeclaredField("ctl"));
+ TAIL = U.objectFieldOffset
+ (BufferedSubscription.class.getDeclaredField("tail"));
+ HEAD = U.objectFieldOffset
+ (BufferedSubscription.class.getDeclaredField("head"));
+ DEMAND = U.objectFieldOffset
+ (BufferedSubscription.class.getDeclaredField("demand"));
+
+ ABASE = U.arrayBaseOffset(Object[].class);
+ int scale = U.arrayIndexScale(Object[].class);
+ if ((scale & (scale - 1)) != 0)
+ throw new Error("data type scale not a power of two");
+ ASHIFT = 31 - Integer.numberOfLeadingZeros(scale);
+ } catch (ReflectiveOperationException e) {
+ throw new Error(e);
+ }
+
+ // Reduce the risk of rare disastrous classloading in first call to
+ // LockSupport.park: https://bugs.openjdk.java.net/browse/JDK-8074773
+ Class<?> ensureLoaded = LockSupport.class;
+ }
+ }
+}