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A bundle project producing JAX-RS RI bundles. The primary artifact is an "all-in-one" OSGi-fied JAX-RS RI bundle (jaxrs-ri.jar). Attached to that are two compressed JAX-RS RI archives. The first archive (jaxrs-ri.zip) consists of binary RI bits and contains the API jar (under "api" directory), RI libraries (under "lib" directory) as well as all external RI dependencies (under "ext" directory). The secondary archive (jaxrs-ri-src.zip) contains buildable JAX-RS RI source bundle and contains the API jar (under "api" directory), RI sources (under "src" directory) as well as all external RI dependencies (under "ext" directory). The second archive also contains "build.xml" ANT script that builds the RI sources. To build the JAX-RS RI simply unzip the archive, cd to the created jaxrs-ri directory and invoke "ant" from the command line.

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/*
 * Copyright (c) 2017, 2019 Oracle and/or its affiliates. All rights reserved.
 *
 * This program and the accompanying materials are made available under the
 * terms of the Eclipse Public License v. 2.0, which is available at
 * http://www.eclipse.org/legal/epl-2.0.
 *
 * This Source Code may also be made available under the following Secondary
 * Licenses when the conditions for such availability set forth in the
 * Eclipse Public License v. 2.0 are satisfied: GNU General Public License,
 * version 2 with the GNU Classpath Exception, which is available at
 * https://www.gnu.org/software/classpath/license.html.
 *
 * SPDX-License-Identifier: EPL-2.0 OR GPL-2.0 WITH Classpath-exception-2.0
 */

package org.glassfish.jersey.internal.util.collection;

import java.util.concurrent.Callable;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.Future;
import java.util.concurrent.FutureTask;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.TimeoutException;
import java.util.function.Function;

/**
 * Cache implementation that relies on FutureTask.
 * Desired value will only be computed once and computed value stored in the cache.
 * The implementation is based on an example from the "Java Concurrency in Practice" book
 * authored by Brian Goetz and company.
 *
 * @param  The type of the key of the cache
 * @param  The type of the values in the cache
 * @author Jakub Podlesak
 */
public class Cache implements Function {

    private static final CycleHandler EMPTY_HANDLER = key -> { };
    private final CycleHandler cycleHandler;
    private final ConcurrentHashMap cache = new ConcurrentHashMap<>();
    private final Function computable;

    /**
     * Create new cache with given computable to compute values.
     * Detected cycles will be ignored as there is a no-op cycle handler registered by default.
     *
     * @param computable function generated the new value.
     */
    @SuppressWarnings("unchecked")
    public Cache(Function computable) {
        this(computable, (CycleHandler) EMPTY_HANDLER);
    }

    /**
     * Create new cache with given computable and cycle handler.
     *
     * @param computable   function generated the new value.
     * @param cycleHandler handler used if the thread cycle is met.
     */
    public Cache(Function computable, CycleHandler cycleHandler) {
        this.computable = computable;
        this.cycleHandler = cycleHandler;
    }

    @Override
    public V apply(final K key) {
        while (true) {
            OriginThreadAwareFuture f = cache.get(key);
            if (f == null) {
                OriginThreadAwareFuture ft = new OriginThreadAwareFuture(key);

                f = cache.putIfAbsent(key, ft);
                if (f == null) {
                    f = ft;
                    ft.run();
                }
            } else {
                final long tid = f.threadId;
                if ((tid != -1) && (Thread.currentThread().getId() == f.threadId)) {
                    cycleHandler.handleCycle(key);
                }
            }
            try {
                return f.get();
            } catch (InterruptedException ex) {
                throw new RuntimeException(ex);
            } catch (ExecutionException ex) {
                cache.remove(key);  // otherwise the exception would be remembered
                Throwable cause = ex.getCause();
                if (cause == null) {
                    throw new RuntimeException(ex);
                }
                if (cause instanceof RuntimeException) {
                    throw (RuntimeException) cause;
                }
                throw new RuntimeException(cause);
            }
        }
    }

    /**
     * Empty cache.
     */
    public void clear() {
        cache.clear();
    }

    /**
     * Returns true if the key has already been cached.
     *
     * @param key item key.
     * @return true if given key is present in the cache.
     */
    public boolean containsKey(final K key) {
        return cache.containsKey(key);
    }

    /**
     * Remove item from the cache.
     *
     * @param key item key.
     */
    public void remove(final K key) {
        cache.remove(key);
    }

    /**
     * Returns the size of the cache
     *
     * @return The number of elements in the cache
     */
    public int size() {
        return cache.size();
    }

    /**
     * Should a cycle be detected during computation of a value
     * for given key, this interface allows client code to register
     * a callback that would get invoked in such a case.
     *
     * @param  Key type.
     */
    public interface CycleHandler {

        /**
         * Handle cycle that was detected while computing a cache value
         * for given key. This method would typically just throw a runtime exception.
         *
         * @param key instance that caused the cycle.
         */
        void handleCycle(K key);
    }

    /**
     * Helper class, that remembers the future task origin thread, so that cycles could be detected.
     * If any thread starts computation for given key and the same thread requests the computed value
     * before the computation stops, a cycle is detected and registered cycle handler is called.
     */
    private class OriginThreadAwareFuture implements Future {
        private final FutureTask future;
        private volatile long threadId;

        OriginThreadAwareFuture(K key) {
            this.threadId = Thread.currentThread().getId();
            Callable eval = () -> {
                try {
                    return computable.apply(key);
                } finally {
                    threadId = -1;
                }
            };
            this.future = new FutureTask<>(eval);
        }

        @Override
        public int hashCode() {
            return future.hashCode();
        }

        @SuppressWarnings("unchecked")
        @Override
        public boolean equals(Object obj) {
            if (obj == null) {
                return false;
            }
            if (getClass() != obj.getClass()) {
                return false;
            }

            final OriginThreadAwareFuture other = (OriginThreadAwareFuture) obj;
            if (this.future != other.future && (this.future == null || !this.future.equals(other.future))) {
                return false;
            }
            return true;
        }

        @Override
        public boolean cancel(boolean mayInterruptIfRunning) {
            return future.cancel(mayInterruptIfRunning);
        }

        @Override
        public boolean isCancelled() {
            return future.isCancelled();
        }

        @Override
        public boolean isDone() {
            return future.isDone();
        }

        @Override
        public V get() throws InterruptedException, ExecutionException {
            return future.get();
        }

        @Override
        public V get(long timeout, TimeUnit unit) throws InterruptedException, ExecutionException, TimeoutException {
            return future.get(timeout, unit);
        }

        public void run() {
            future.run();
        }
    }
}
 















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