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| 1 | +package scala.concurrent.java8 |
| 2 | + |
| 3 | +import scala.concurrent.{ Future, Promise, ExecutionContext, ExecutionContextExecutorService, ExecutionContextExecutor, impl } |
| 4 | +import java.util.concurrent.{ CompletionStage, Executor, ExecutorService, CompletableFuture } |
| 5 | +import scala.util.{ Try, Success, Failure } |
| 6 | +import java.util.function.{ BiConsumer, Function ⇒ JF, Consumer, BiFunction } |
| 7 | + |
| 8 | +/** |
| 9 | + * This class contains static methods which convert between Java CompletionStage |
| 10 | + * and Scala Future. This is useful when mediating between Scala and Java |
| 11 | + * libraries with asynchronous APIs. |
| 12 | + * |
| 13 | + * Note that the bridge is implemented at the read-only side of asynchronous |
| 14 | + * handles, namely scala.concurrent.Future instead of scala.concurrent.Promise |
| 15 | + * and CompletionStage instead of CompletableFuture. This is intentional, as |
| 16 | + * the semantics of bridging the write-handles would be prone to race |
| 17 | + * conditions; if both ends (CompletableFuture and Promise) are completed |
| 18 | + * independently at the same time, they may contain different values afterwards. |
| 19 | + * For this reason, <code>toCompletableFuture()</code> is not supported on the |
| 20 | + * created CompletionStages. |
| 21 | + * |
| 22 | + * Example usage: |
| 23 | + * |
| 24 | + * {{{ |
| 25 | + * import java.util.concurrent.CompletionStage; |
| 26 | + * import scala.concurrent.Future; |
| 27 | + * import static scala.concurrent.java8.FutureConverter.*; |
| 28 | + * |
| 29 | + * final CompletionStage<String> cs = ... // from an async Java API |
| 30 | + * final Future<String> f = toScala(cs); |
| 31 | + * ... |
| 32 | + * final Future<Integer> f2 = ... // from an async Scala API |
| 33 | + * final CompletionStage<Integer> cs2 = toJava(f2); |
| 34 | + * }}} |
| 35 | + */ |
| 36 | +object FutureConverter { |
| 37 | + |
| 38 | + private class CF[T] extends CompletableFuture[T] with (Try[T] => Unit) { |
| 39 | + override def apply(t: Try[T]): Unit = t match { |
| 40 | + case Success(v) ⇒ complete(v) |
| 41 | + case Failure(e) ⇒ completeExceptionally(e) |
| 42 | + } |
| 43 | + |
| 44 | + /* |
| 45 | + * Ensure that completions of this future cannot hold the Scala Future’s completer hostage. |
| 46 | + */ |
| 47 | + override def thenApply[U](fn: JF[_ >: T, _ <: U]): CompletableFuture[U] = thenApplyAsync(fn) |
| 48 | + override def thenAccept(fn: Consumer[_ >: T]): CompletableFuture[Void] = thenAcceptAsync(fn) |
| 49 | + override def thenRun(fn: Runnable): CompletableFuture[Void] = thenRunAsync(fn) |
| 50 | + override def thenCombine[U, V](cs: CompletionStage[_ <: U], fn: BiFunction[_ >: T, _ >: U, _ <: V]): CompletableFuture[V] = thenCombineAsync(cs, fn) |
| 51 | + override def thenAcceptBoth[U](cs: CompletionStage[_ <: U], fn: BiConsumer[_ >: T, _ >: U]): CompletableFuture[Void] = thenAcceptBothAsync(cs, fn) |
| 52 | + override def runAfterBoth(cs: CompletionStage[_], fn: Runnable): CompletableFuture[Void] = runAfterBothAsync(cs, fn) |
| 53 | + override def applyToEither[U](cs: CompletionStage[_ <: T], fn: JF[_ >: T, U]): CompletableFuture[U] = applyToEitherAsync(cs, fn) |
| 54 | + override def acceptEither(cs: CompletionStage[_ <: T], fn: Consumer[_ >: T]): CompletableFuture[Void] = acceptEitherAsync(cs, fn) |
| 55 | + override def runAfterEither(cs: CompletionStage[_], fn: Runnable): CompletableFuture[Void] = runAfterEitherAsync(cs, fn) |
| 56 | + override def thenCompose[U](fn: JF[_ >: T, _ <: CompletionStage[U]]): CompletableFuture[U] = thenComposeAsync(fn) |
| 57 | + override def whenComplete(fn: BiConsumer[_ >: T, _ >: Throwable]): CompletableFuture[T] = whenCompleteAsync(fn) |
| 58 | + override def handle[U](fn: BiFunction[_ >: T, Throwable, _ <: U]): CompletableFuture[U] = handleAsync(fn) |
| 59 | + override def exceptionally(fn: JF[Throwable, _ <: T]): CompletableFuture[T] = { |
| 60 | + val cf = new CompletableFuture[T] |
| 61 | + whenCompleteAsync(new BiConsumer[T, Throwable] { |
| 62 | + override def accept(t: T, e: Throwable): Unit = { |
| 63 | + if (e == null) cf.complete(t) |
| 64 | + else { |
| 65 | + val n: AnyRef = |
| 66 | + try { |
| 67 | + fn(e).asInstanceOf[AnyRef] |
| 68 | + } catch { |
| 69 | + case thr: Throwable ⇒ cf.completeExceptionally(thr); this |
| 70 | + } |
| 71 | + if (n ne this) cf.complete(n.asInstanceOf[T]) |
| 72 | + } |
| 73 | + } |
| 74 | + }) |
| 75 | + cf |
| 76 | + } |
| 77 | + |
| 78 | + override def toCompletableFuture(): CompletableFuture[T] = |
| 79 | + throw new UnsupportedOperationException("this CompletionStage represents a read-only Scala Future") |
| 80 | + |
| 81 | + override def toString: String = super[CompletableFuture].toString |
| 82 | + } |
| 83 | + |
| 84 | + /** |
| 85 | + * Returns a CompletionStage that will be completed with the same value or |
| 86 | + * exception as the given Scala Future when that completes. Since the Future is a read-only |
| 87 | + * representation, this CompletionStage does not support the |
| 88 | + * <code>toCompletableFuture</code> method. The semantics of Scala Future |
| 89 | + * demand that all callbacks are invoked asynchronously by default, therefore |
| 90 | + * the returned CompletionStage routes all calls to synchronous |
| 91 | + * transformations to their asynchronous counterparts, i.e. |
| 92 | + * <code>thenRun</code> will internally call <code>thenRunAsync</code>. |
| 93 | + * |
| 94 | + * @param f The Scala Future which may eventually supply the completion for |
| 95 | + * the returned CompletionStage |
| 96 | + * @return a CompletionStage that runs all callbacks asynchronously and does |
| 97 | + * not support the CompletableFuture interface |
| 98 | + */ |
| 99 | + def toJava[T](f: Future[T]): CompletionStage[T] = { |
| 100 | + val cf = new CF[T] |
| 101 | + implicit val ec = Future.InternalCallbackExecutor |
| 102 | + f onComplete cf |
| 103 | + cf |
| 104 | + } |
| 105 | + |
| 106 | + private class P[T] extends impl.Promise.DefaultPromise[T] with BiConsumer[T, Throwable] { |
| 107 | + override def accept(v: T, e: Throwable): Unit = { |
| 108 | + if (e == null) complete(Success(v)) |
| 109 | + else complete(Failure(e)) |
| 110 | + } |
| 111 | + } |
| 112 | + |
| 113 | + /** |
| 114 | + * Returns a Scala Future that will be completed with the same value or |
| 115 | + * exception as the given CompletionStage when that completes. Transformations |
| 116 | + * of the returned Future are executed asynchronously as specified by the |
| 117 | + * ExecutionContext that is given to the combinator methods. |
| 118 | + * |
| 119 | + * @param cs The CompletionStage which may eventually supply the completion |
| 120 | + * for the returned Scala Future |
| 121 | + * @return a Scala Future that represents the CompletionStage's completion |
| 122 | + */ |
| 123 | + def toScala[T](cs: CompletionStage[T]): Future[T] = { |
| 124 | + val p = new P[T] |
| 125 | + cs whenComplete p |
| 126 | + p.future |
| 127 | + } |
| 128 | + |
| 129 | + /** |
| 130 | + * Creates an ExecutionContext from a given ExecutorService, using the given |
| 131 | + * Consumer for reporting errors. The latter can be created as in the |
| 132 | + * following example: |
| 133 | + * |
| 134 | + * {{{ |
| 135 | + * final ExecutionContext ec = Converter.fromExecutorService(es, thr -> thr.printStackTrace()); |
| 136 | + * }}} |
| 137 | + * |
| 138 | + * @param e an ExecutorService |
| 139 | + * @param reporter a Consumer for reporting errors during execution |
| 140 | + * @return an ExecutionContext backed by the given ExecutorService |
| 141 | + */ |
| 142 | + def fromExecutorService(e: ExecutorService, reporter: Consumer[Throwable]): ExecutionContextExecutorService = |
| 143 | + ExecutionContext.fromExecutorService(e, reporter.accept) |
| 144 | + |
| 145 | + /** |
| 146 | + * Creates an ExecutionContext from a given ExecutorService, using the |
| 147 | + * default reporter for uncaught exceptions which will just call |
| 148 | + * <code>.printStackTrace()</code>. |
| 149 | + * |
| 150 | + * @param e an ExecutorService |
| 151 | + * @return an ExecutionContext backed by the given ExecutorService |
| 152 | + */ |
| 153 | + def fromExecutorService(e: ExecutorService): ExecutionContextExecutorService = |
| 154 | + ExecutionContext.fromExecutorService(e, ExecutionContext.defaultReporter) |
| 155 | + |
| 156 | + /** |
| 157 | + * Creates an ExecutionContext from a given Executor, using the given |
| 158 | + * Consumer for reporting errors. The latter can be created as in the |
| 159 | + * following example: |
| 160 | + * |
| 161 | + * {{{ |
| 162 | + * final ExecutionContext ec = Converter.fromExecutor(es, thr -> thr.printStackTrace()); |
| 163 | + * }}} |
| 164 | + * |
| 165 | + * @param e an Executor |
| 166 | + * @param reporter a Consumer for reporting errors during execution |
| 167 | + * @return an ExecutionContext backed by the given Executor |
| 168 | + */ |
| 169 | + def fromExecutor(e: Executor, reporter: Consumer[Throwable]): ExecutionContextExecutor = |
| 170 | + ExecutionContext.fromExecutor(e, reporter.accept) |
| 171 | + |
| 172 | + /** |
| 173 | + * Creates an ExecutionContext from a given Executor, using the |
| 174 | + * default reporter for uncaught exceptions which will just call |
| 175 | + * <code>.printStackTrace()</code>. |
| 176 | + * |
| 177 | + * @param e an Executor |
| 178 | + * @return an ExecutionContext backed by the given Executor |
| 179 | + */ |
| 180 | + def fromExecutor(e: Executor): ExecutionContextExecutor = |
| 181 | + ExecutionContext.fromExecutor(e, ExecutionContext.defaultReporter) |
| 182 | + |
| 183 | + /** |
| 184 | + * Return the global ExecutionContext for Scala Futures. |
| 185 | + * |
| 186 | + * @return the ExecutionContext |
| 187 | + */ |
| 188 | + def globalExecutionContext: ExecutionContext = ExecutionContext.global |
| 189 | + |
| 190 | + /** |
| 191 | + * Construct an empty <code>scala.concurrent.Promise</code>. |
| 192 | + * |
| 193 | + * @return a Promise which is not yet completed |
| 194 | + */ |
| 195 | + def promise[T](): Promise[T] = Promise() |
| 196 | + |
| 197 | + /** |
| 198 | + * Construct an already fulfilled <code>scala.concurrent.Promise</code> which holds the given value. |
| 199 | + * |
| 200 | + * @return the fulfilled Promise |
| 201 | + */ |
| 202 | + def keptPromise[T](v: T): Promise[T] = Promise.successful(v) |
| 203 | + |
| 204 | + /** |
| 205 | + * Construct an already fulfilled <code>scala.concurrent.Promise</code> which holds the given failure. |
| 206 | + * |
| 207 | + * @return the fulfilled Promise |
| 208 | + */ |
| 209 | + def failedPromise[T](ex: Throwable): Promise[T] = Promise.failed(ex) |
| 210 | + |
| 211 | +} |
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