| 1 | /** |
| 2 | * Licensed to jclouds, Inc. (jclouds) under one or more |
| 3 | * contributor license agreements. See the NOTICE file |
| 4 | * distributed with this work for additional information |
| 5 | * regarding copyright ownership. jclouds licenses this file |
| 6 | * to you under the Apache License, Version 2.0 (the |
| 7 | * "License"); you may not use this file except in compliance |
| 8 | * with the License. You may obtain a copy of the License at |
| 9 | * |
| 10 | * http://www.apache.org/licenses/LICENSE-2.0 |
| 11 | * |
| 12 | * Unless required by applicable law or agreed to in writing, |
| 13 | * software distributed under the License is distributed on an |
| 14 | * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY |
| 15 | * KIND, either express or implied. See the License for the |
| 16 | * specific language governing permissions and limitations |
| 17 | * under the License. |
| 18 | */ |
| 19 | package org.jclouds.concurrent; |
| 20 | |
| 21 | import static com.google.common.base.Preconditions.checkNotNull; |
| 22 | |
| 23 | import java.util.concurrent.ExecutionException; |
| 24 | import java.util.concurrent.Executor; |
| 25 | import java.util.concurrent.ExecutorService; |
| 26 | import java.util.concurrent.Future; |
| 27 | import java.util.concurrent.TimeUnit; |
| 28 | import java.util.concurrent.TimeoutException; |
| 29 | import java.util.concurrent.atomic.AtomicBoolean; |
| 30 | |
| 31 | import com.google.common.annotations.Beta; |
| 32 | import com.google.common.annotations.VisibleForTesting; |
| 33 | import com.google.common.base.Function; |
| 34 | import com.google.common.collect.ForwardingObject; |
| 35 | import com.google.common.util.concurrent.ExecutionList; |
| 36 | import com.google.common.util.concurrent.ForwardingFuture; |
| 37 | import com.google.common.util.concurrent.ListenableFuture; |
| 38 | |
| 39 | /** |
| 40 | * functions related to or replacing those in {@link com.google.common.util.concurrent.Futures} |
| 41 | * |
| 42 | * @author Adrian Cole |
| 43 | */ |
| 44 | @Beta |
| 45 | public class Futures { |
| 46 | @VisibleForTesting |
| 47 | static class CallGetAndRunExecutionList<T> implements Runnable { |
| 48 | private final Future<T> delegate; |
| 49 | private final ExecutionList executionList; |
| 50 | |
| 51 | public CallGetAndRunExecutionList(Future<T> delegate, ExecutionList executionList) { |
| 52 | this.delegate = checkNotNull(delegate, "delegate"); |
| 53 | this.executionList = checkNotNull(executionList, "executionList"); |
| 54 | } |
| 55 | |
| 56 | @Override |
| 57 | public void run() { |
| 58 | try { |
| 59 | delegate.get(); |
| 60 | } catch (InterruptedException e) { |
| 61 | // This thread was interrupted. This should never happen, so we |
| 62 | // throw an IllegalStateException. |
| 63 | Thread.currentThread().interrupt(); |
| 64 | // TODO we cannot inspect the executionList at the moment to make a reasonable |
| 65 | // toString() |
| 66 | throw new IllegalStateException(String.format( |
| 67 | "interrupted calling get() on [%s], so could not run listeners", delegate), e); |
| 68 | } catch (Throwable e) { |
| 69 | // ExecutionException / CancellationException / RuntimeException |
| 70 | // The task is done, run the listeners. |
| 71 | } |
| 72 | executionList.execute(); |
| 73 | } |
| 74 | |
| 75 | @Override |
| 76 | public String toString() { |
| 77 | return "[delegate=" + delegate + ", executionList=" + executionList + "]"; |
| 78 | } |
| 79 | } |
| 80 | |
| 81 | // Adapted from Guava |
| 82 | // |
| 83 | // * to allow us to enforce supply of an adapterExecutor |
| 84 | // note that this is done so that we can operate in Google AppEngine which |
| 85 | // restricts thread creation |
| 86 | // * to allow us to print debug info about what the delegate was doing |
| 87 | public static class FutureListener<T> { |
| 88 | |
| 89 | final ExecutorService adapterExecutor; |
| 90 | |
| 91 | // The execution list to hold our listeners. |
| 92 | private final ExecutionList executionList = new ExecutionList(); |
| 93 | |
| 94 | // This allows us to only start up a thread waiting on the delegate future |
| 95 | // when the first listener is added. |
| 96 | private final AtomicBoolean hasListeners = new AtomicBoolean(false); |
| 97 | |
| 98 | // The delegate future. |
| 99 | private final Future<T> delegate; |
| 100 | |
| 101 | static <T> FutureListener<T> create(Future<T> delegate, ExecutorService adapterExecutor) { |
| 102 | return new FutureListener<T>(delegate, adapterExecutor); |
| 103 | } |
| 104 | |
| 105 | private FutureListener(Future<T> delegate, ExecutorService adapterExecutor) { |
| 106 | this.delegate = checkNotNull(delegate, "delegate"); |
| 107 | this.adapterExecutor = checkNotNull(adapterExecutor, "adapterExecutor"); |
| 108 | } |
| 109 | |
| 110 | public void addListener(Runnable listener, Executor exec) { |
| 111 | executionList.add(listener, exec); |
| 112 | |
| 113 | // When a listener is first added, we run a task that will wait for |
| 114 | // the delegate to finish, and when it is done will run the listeners. |
| 115 | if (hasListeners.compareAndSet(false, true)) { |
| 116 | if (delegate.isDone()) { |
| 117 | // If the delegate is already done, run the execution list |
| 118 | // immediately on the current thread. |
| 119 | executionList.execute(); |
| 120 | return; |
| 121 | } |
| 122 | adapterExecutor.execute(new CallGetAndRunExecutionList<T>(delegate, executionList)); |
| 123 | } |
| 124 | } |
| 125 | |
| 126 | Future<T> getFuture() { |
| 127 | return delegate; |
| 128 | } |
| 129 | |
| 130 | ExecutorService getExecutor() { |
| 131 | return adapterExecutor; |
| 132 | } |
| 133 | } |
| 134 | |
| 135 | public static class ListenableFutureAdapter<T> extends ForwardingFuture<T> implements ListenableFuture<T> { |
| 136 | final FutureListener<T> futureListener; |
| 137 | |
| 138 | static <T> ListenableFutureAdapter<T> create(Future<T> future, ExecutorService executor) { |
| 139 | return new ListenableFutureAdapter<T>(future, executor); |
| 140 | } |
| 141 | |
| 142 | private ListenableFutureAdapter(Future<T> future, ExecutorService executor) { |
| 143 | this.futureListener = FutureListener.create(future, executor); |
| 144 | } |
| 145 | |
| 146 | @Override |
| 147 | protected Future<T> delegate() { |
| 148 | return futureListener.getFuture(); |
| 149 | } |
| 150 | |
| 151 | @Override |
| 152 | public void addListener(Runnable listener, Executor exec) { |
| 153 | futureListener.addListener(listener, exec); |
| 154 | } |
| 155 | |
| 156 | } |
| 157 | |
| 158 | public static class LazyListenableFutureFunctionAdapter<I, O> extends ForwardingObject implements |
| 159 | ListenableFuture<O> { |
| 160 | private final FutureListener<I> futureListener; |
| 161 | private final Function<? super I, ? extends O> function; |
| 162 | |
| 163 | static <I, O> LazyListenableFutureFunctionAdapter<I, O> create(Future<I> future, |
| 164 | Function<? super I, ? extends O> function, ExecutorService executor) { |
| 165 | return new LazyListenableFutureFunctionAdapter<I, O>(future, function, executor); |
| 166 | } |
| 167 | |
| 168 | static <I, O> LazyListenableFutureFunctionAdapter<I, O> create(FutureListener<I> futureListener, |
| 169 | Function<? super I, ? extends O> function) { |
| 170 | return new LazyListenableFutureFunctionAdapter<I, O>(futureListener, function); |
| 171 | } |
| 172 | |
| 173 | private LazyListenableFutureFunctionAdapter(Future<I> future, Function<? super I, ? extends O> function, |
| 174 | ExecutorService executor) { |
| 175 | this(FutureListener.create(future, executor), function); |
| 176 | } |
| 177 | |
| 178 | private LazyListenableFutureFunctionAdapter(FutureListener<I> futureListener, |
| 179 | Function<? super I, ? extends O> function) { |
| 180 | this.futureListener = checkNotNull(futureListener, "futureListener"); |
| 181 | this.function = checkNotNull(function, "function"); |
| 182 | } |
| 183 | |
| 184 | /* |
| 185 | * Concurrency detail: |
| 186 | * |
| 187 | * <p>To preserve the idempotency of calls to this.get(*) calls to the function are only |
| 188 | * applied once. A lock is required to prevent multiple applications of the function. The |
| 189 | * calls to future.get(*) are performed outside the lock, as is required to prevent calls to |
| 190 | * get(long, TimeUnit) to persist beyond their timeout. |
| 191 | * |
| 192 | * <p>Calls to future.get(*) on every call to this.get(*) also provide the cancellation |
| 193 | * behavior for this. |
| 194 | * |
| 195 | * <p>(Consider: in thread A, call get(), in thread B call get(long, TimeUnit). Thread B may |
| 196 | * have to wait for Thread A to finish, which would be unacceptable.) |
| 197 | * |
| 198 | * <p>Note that each call to Future<O>.get(*) results in a call to Future<I>.get(*), but the |
| 199 | * function is only applied once, so Future<I>.get(*) is assumed to be idempotent. |
| 200 | */ |
| 201 | |
| 202 | private final Object lock = new Object(); |
| 203 | private boolean set = false; |
| 204 | private O value = null; |
| 205 | |
| 206 | @Override |
| 207 | public O get() throws InterruptedException, ExecutionException { |
| 208 | return apply(futureListener.getFuture().get()); |
| 209 | } |
| 210 | |
| 211 | @Override |
| 212 | public O get(long timeout, TimeUnit unit) throws InterruptedException, ExecutionException, TimeoutException { |
| 213 | return apply(futureListener.getFuture().get(timeout, unit)); |
| 214 | } |
| 215 | |
| 216 | private O apply(I raw) { |
| 217 | synchronized (lock) { |
| 218 | if (!set) { |
| 219 | value = function.apply(raw); |
| 220 | set = true; |
| 221 | } |
| 222 | return value; |
| 223 | } |
| 224 | } |
| 225 | |
| 226 | @Override |
| 227 | public boolean cancel(boolean mayInterruptIfRunning) { |
| 228 | return futureListener.getFuture().cancel(mayInterruptIfRunning); |
| 229 | } |
| 230 | |
| 231 | @Override |
| 232 | public boolean isCancelled() { |
| 233 | return futureListener.getFuture().isCancelled(); |
| 234 | } |
| 235 | |
| 236 | @Override |
| 237 | public boolean isDone() { |
| 238 | return futureListener.getFuture().isDone(); |
| 239 | } |
| 240 | |
| 241 | @Override |
| 242 | public void addListener(Runnable listener, Executor exec) { |
| 243 | futureListener.addListener(listener, exec); |
| 244 | } |
| 245 | |
| 246 | @Override |
| 247 | protected Object delegate() { |
| 248 | return futureListener.getFuture(); |
| 249 | } |
| 250 | |
| 251 | } |
| 252 | |
| 253 | /** |
| 254 | * Just like {@code Futures#compose} except that we check the type of the executorService before |
| 255 | * creating the Future. If we are single threaded, invoke the function lazy as opposed to |
| 256 | * chaining, so that we don't invoke get() early. |
| 257 | */ |
| 258 | public static <I, O> ListenableFuture<O> compose(Future<I> future, final Function<? super I, ? extends O> function, |
| 259 | ExecutorService executorService) { |
| 260 | if (future instanceof Futures.ListenableFutureAdapter<?>) { |
| 261 | Futures.ListenableFutureAdapter<I> lf = (ListenableFutureAdapter<I>) future; |
| 262 | if (lf.futureListener.adapterExecutor.getClass().isAnnotationPresent(SingleThreaded.class)) |
| 263 | return Futures.LazyListenableFutureFunctionAdapter.create( |
| 264 | ((org.jclouds.concurrent.Futures.ListenableFutureAdapter<I>) future).futureListener, function); |
| 265 | else |
| 266 | return com.google.common.util.concurrent.Futures.transform(lf, function, executorService); |
| 267 | } else if (executorService.getClass().isAnnotationPresent(SingleThreaded.class)) { |
| 268 | return Futures.LazyListenableFutureFunctionAdapter.create(future, function, executorService); |
| 269 | } else { |
| 270 | return com.google.common.util.concurrent.Futures.transform(Futures.makeListenable(future, executorService), |
| 271 | function, executorService); |
| 272 | } |
| 273 | } |
| 274 | |
| 275 | /** |
| 276 | * Just like {@code Futures#makeListenable} except that we pass in an executorService. |
| 277 | * <p/> |
| 278 | * Temporary hack until http://code.google.com/p/guava-libraries/issues/detail?id=317 is fixed. |
| 279 | */ |
| 280 | public static <T> ListenableFuture<T> makeListenable(Future<T> future, ExecutorService executorService) { |
| 281 | if (future instanceof ListenableFuture<?>) { |
| 282 | return (ListenableFuture<T>) future; |
| 283 | } |
| 284 | return ListenableFutureAdapter.create(future, executorService); |
| 285 | } |
| 286 | |
| 287 | } |