8210971: Add exception handling methods to CompletionStage and CompletableFuture

Reviewed-by: martin, chegar

src/java.base/share/classes/java/util/concurrent/CompletableFuture.java

@@ -957,17 +957,17 @@ public class CompletableFuture<T> implements Future<T>, CompletionStage<T> {
     @SuppressWarnings("serial")
     static final class UniExceptionally<T> extends UniCompletion<T,T> {
         Function<? super Throwable, ? extends T> fn;
-        UniExceptionally(CompletableFuture<T> dep, CompletableFuture<T> src,
+        UniExceptionally(Executor executor,
+                         CompletableFuture<T> dep, CompletableFuture<T> src,
                          Function<? super Throwable, ? extends T> fn) {
-            super(null, dep, src); this.fn = fn;
+            super(executor, dep, src); this.fn = fn;
         }
-        final CompletableFuture<T> tryFire(int mode) { // never ASYNC
-            // assert mode != ASYNC;
+        final CompletableFuture<T> tryFire(int mode) {
             CompletableFuture<T> d; CompletableFuture<T> a;
             Object r; Function<? super Throwable, ? extends T> f;
             if ((d = dep) == null || (f = fn) == null
                 || (a = src) == null || (r = a.result) == null
-                || !d.uniExceptionally(r, f, this))
+                || !d.uniExceptionally(r, f, mode > 0 ? null : this))
                 return null;
             dep = null; src = null; fn = null;
             return d.postFire(a, mode);
@@ -980,11 +980,11 @@ public class CompletableFuture<T> implements Future<T>, CompletionStage<T> {
         Throwable x;
         if (result == null) {
             try {
-                if (r instanceof AltResult && (x = ((AltResult)r).ex) != null) {
-                    if (c != null && !c.claim())
-                        return false;
+                if (c != null && !c.claim())
+                    return false;
+                if (r instanceof AltResult && (x = ((AltResult)r).ex) != null)
                     completeValue(f.apply(x));
-                } else
+                else
                     internalComplete(r);
             } catch (Throwable ex) {
                 completeThrowable(ex);
@@ -994,14 +994,88 @@ public class CompletableFuture<T> implements Future<T>, CompletionStage<T> {
     }
 
     private CompletableFuture<T> uniExceptionallyStage(
-        Function<Throwable, ? extends T> f) {
+        Executor e, Function<Throwable, ? extends T> f) {
         if (f == null) throw new NullPointerException();
         CompletableFuture<T> d = newIncompleteFuture();
         Object r;
         if ((r = result) == null)
-            unipush(new UniExceptionally<T>(d, this, f));
-        else
+            unipush(new UniExceptionally<T>(e, d, this, f));
+        else if (e == null)
             d.uniExceptionally(r, f, null);
+        else {
+            try {
+                e.execute(new UniExceptionally<T>(null, d, this, f));
+            } catch (Throwable ex) {
+                d.result = encodeThrowable(ex);
+            }
+        }
+        return d;
+    }
+
+    @SuppressWarnings("serial")
+    static final class UniComposeExceptionally<T> extends UniCompletion<T,T> {
+        Function<Throwable, ? extends CompletionStage<T>> fn;
+        UniComposeExceptionally(Executor executor, CompletableFuture<T> dep,
+                                CompletableFuture<T> src,
+                                Function<Throwable, ? extends CompletionStage<T>> fn) {
+            super(executor, dep, src); this.fn = fn;
+        }
+        final CompletableFuture<T> tryFire(int mode) {
+            CompletableFuture<T> d; CompletableFuture<T> a;
+            Function<Throwable, ? extends CompletionStage<T>> f;
+            Object r; Throwable x;
+            if ((d = dep) == null || (f = fn) == null
+                || (a = src) == null || (r = a.result) == null)
+                return null;
+            if (d.result == null) {
+                if ((r instanceof AltResult) &&
+                    (x = ((AltResult)r).ex) != null) {
+                    try {
+                        if (mode <= 0 && !claim())
+                            return null;
+                        CompletableFuture<T> g = f.apply(x).toCompletableFuture();
+                        if ((r = g.result) != null)
+                            d.completeRelay(r);
+                        else {
+                            g.unipush(new UniRelay<T,T>(d, g));
+                            if (d.result == null)
+                                return null;
+                        }
+                    } catch (Throwable ex) {
+                        d.completeThrowable(ex);
+                    }
+                }
+                else
+                    d.internalComplete(r);
+            }
+            dep = null; src = null; fn = null;
+            return d.postFire(a, mode);
+        }
+    }
+
+    private CompletableFuture<T> uniComposeExceptionallyStage(
+        Executor e, Function<Throwable, ? extends CompletionStage<T>> f) {
+        if (f == null) throw new NullPointerException();
+        CompletableFuture<T> d = newIncompleteFuture();
+        Object r, s; Throwable x;
+        if ((r = result) == null)
+            unipush(new UniComposeExceptionally<T>(e, d, this, f));
+        else if (!(r instanceof AltResult) || (x = ((AltResult)r).ex) == null)
+            d.internalComplete(r);
+        else
+            try {
+                if (e != null)
+                    e.execute(new UniComposeExceptionally<T>(null, d, this, f));
+                else {
+                    CompletableFuture<T> g = f.apply(x).toCompletableFuture();
+                    if ((s = g.result) != null)
+                        d.result = encodeRelay(s);
+                    else
+                        g.unipush(new UniRelay<T,T>(d, g));
+                }
+            } catch (Throwable ex) {
+                d.result = encodeThrowable(ex);
+            }
         return d;
     }
 
@@ -1093,7 +1167,7 @@ public class CompletableFuture<T> implements Future<T>, CompletionStage<T> {
         Object r, s; Throwable x;
         if ((r = result) == null)
             unipush(new UniCompose<T,V>(e, d, this, f));
-        else if (e == null) {
+        else {
             if (r instanceof AltResult) {
                 if ((x = ((AltResult)r).ex) != null) {
                     d.result = encodeThrowable(x, r);
@@ -1102,23 +1176,20 @@ public class CompletableFuture<T> implements Future<T>, CompletionStage<T> {
                 r = null;
             }
             try {
-                @SuppressWarnings("unchecked") T t = (T) r;
-                CompletableFuture<V> g = f.apply(t).toCompletableFuture();
-                if ((s = g.result) != null)
-                    d.result = encodeRelay(s);
+                if (e != null)
+                    e.execute(new UniCompose<T,V>(null, d, this, f));
                 else {
-                    g.unipush(new UniRelay<V,V>(d, g));
+                    @SuppressWarnings("unchecked") T t = (T) r;
+                    CompletableFuture<V> g = f.apply(t).toCompletableFuture();
+                    if ((s = g.result) != null)
+                        d.result = encodeRelay(s);
+                    else
+                        g.unipush(new UniRelay<V,V>(d, g));
                 }
             } catch (Throwable ex) {
                 d.result = encodeThrowable(ex);
             }
         }
-        else
-            try {
-                e.execute(new UniCompose<T,V>(null, d, this, f));
-            } catch (Throwable ex) {
-                d.result = encodeThrowable(ex);
-            }
         return d;
     }
 
@@ -1898,7 +1969,7 @@ public class CompletableFuture<T> implements Future<T>, CompletionStage<T> {
      * Creates a new complete CompletableFuture with given encoded result.
      */
     CompletableFuture(Object r) {
-        this.result = r;
+        RESULT.setRelease(this, r);
     }
 
     /**
@@ -2285,28 +2356,36 @@ public class CompletableFuture<T> implements Future<T>, CompletionStage<T> {
         return this;
     }
 
-    // not in interface CompletionStage
-
-    /**
-     * Returns a new CompletableFuture that is completed when this
-     * CompletableFuture completes, with the result of the given
-     * function of the exception triggering this CompletableFuture's
-     * completion when it completes exceptionally; otherwise, if this
-     * CompletableFuture completes normally, then the returned
-     * CompletableFuture also completes normally with the same value.
-     * Note: More flexible versions of this functionality are
-     * available using methods {@code whenComplete} and {@code handle}.
-     *
-     * @param fn the function to use to compute the value of the
-     * returned CompletableFuture if this CompletableFuture completed
-     * exceptionally
-     * @return the new CompletableFuture
-     */
     public CompletableFuture<T> exceptionally(
         Function<Throwable, ? extends T> fn) {
-        return uniExceptionallyStage(fn);
+        return uniExceptionallyStage(null, fn);
     }
 
+    public CompletableFuture<T> exceptionallyAsync(
+        Function<Throwable, ? extends T> fn) {
+        return uniExceptionallyStage(defaultExecutor(), fn);
+    }
+
+    public CompletableFuture<T> exceptionallyAsync(
+        Function<Throwable, ? extends T> fn, Executor executor) {
+        return uniExceptionallyStage(screenExecutor(executor), fn);
+    }
+
+    public CompletableFuture<T> exceptionallyCompose(
+        Function<Throwable, ? extends CompletionStage<T>> fn) {
+        return uniComposeExceptionallyStage(null, fn);
+    }
+
+    public CompletableFuture<T> exceptionallyComposeAsync(
+        Function<Throwable, ? extends CompletionStage<T>> fn) {
+        return uniComposeExceptionallyStage(defaultExecutor(), fn);
+    }
+
+    public CompletableFuture<T> exceptionallyComposeAsync(
+        Function<Throwable, ? extends CompletionStage<T>> fn,
+        Executor executor) {
+        return uniComposeExceptionallyStage(screenExecutor(executor), fn);
+    }
 
     /* ------------- Arbitrary-arity constructions -------------- */
 

src/java.base/share/classes/java/util/concurrent/CompletionStage.java

@@ -850,6 +850,130 @@ public interface CompletionStage<T> {
     public CompletionStage<T> exceptionally
         (Function<Throwable, ? extends T> fn);
 
+    /**
+     * Returns a new CompletionStage that, when this stage completes
+     * exceptionally, is executed with this stage's exception as the
+     * argument to the supplied function, using this stage's default
+     * asynchronous execution facility.  Otherwise, if this stage
+     * completes normally, then the returned stage also completes
+     * normally with the same value.
+     *
+     * @implSpec The default implementation invokes {@link #handle},
+     * relaying to {@link #handleAsync} on exception, then {@link
+     * #thenCompose} for result.
+     *
+     * @param fn the function to use to compute the value of the
+     * returned CompletionStage if this CompletionStage completed
+     * exceptionally
+     * @return the new CompletionStage
+     * @since 12
+     */
+    public default CompletionStage<T> exceptionallyAsync
+        (Function<Throwable, ? extends T> fn) {
+        return handle((r, ex) -> (ex == null)
+                      ? this
+                      : this.<T>handleAsync((r1, ex1) -> fn.apply(ex1)))
+            .thenCompose(Function.identity());
+    }
+
+    /**
+     * Returns a new CompletionStage that, when this stage completes
+     * exceptionally, is executed with this stage's exception as the
+     * argument to the supplied function, using the supplied Executor.
+     * Otherwise, if this stage completes normally, then the returned
+     * stage also completes normally with the same value.
+     *
+     * @implSpec The default implementation invokes {@link #handle},
+     * relaying to {@link #handleAsync} on exception, then {@link
+     * #thenCompose} for result.
+     *
+     * @param fn the function to use to compute the value of the
+     * returned CompletionStage if this CompletionStage completed
+     * exceptionally
+     * @param executor the executor to use for asynchronous execution
+     * @return the new CompletionStage
+     * @since 12
+     */
+    public default CompletionStage<T> exceptionallyAsync
+        (Function<Throwable, ? extends T> fn, Executor executor) {
+        return handle((r, ex) -> (ex == null)
+                      ? this
+                      : this.<T>handleAsync((r1, ex1) -> fn.apply(ex1), executor))
+            .thenCompose(Function.identity());
+    }
+
+    /**
+     * Returns a new CompletionStage that, when this stage completes
+     * exceptionally, is composed using the results of the supplied
+     * function applied to this stage's exception.
+     *
+     * @implSpec The default implementation invokes {@link #handle},
+     * invoking the given function on exception, then {@link
+     * #thenCompose} for result.
+     *
+     * @param fn the function to use to compute the returned
+     * CompletionStage if this CompletionStage completed exceptionally
+     * @return the new CompletionStage
+     * @since 12
+     */
+    public default CompletionStage<T> exceptionallyCompose
+        (Function<Throwable, ? extends CompletionStage<T>> fn) {
+        return handle((r, ex) -> (ex == null)
+                      ? this
+                      : fn.apply(ex))
+            .thenCompose(Function.identity());
+    }
+
+    /**
+     * Returns a new CompletionStage that, when this stage completes
+     * exceptionally, is composed using the results of the supplied
+     * function applied to this stage's exception, using this stage's
+     * default asynchronous execution facility.
+     *
+     * @implSpec The default implementation invokes {@link #handle},
+     * relaying to {@link #handleAsync} on exception, then {@link
+     * #thenCompose} for result.
+     *
+     * @param fn the function to use to compute the returned
+     * CompletionStage if this CompletionStage completed exceptionally
+     * @return the new CompletionStage
+     * @since 12
+     */
+    public default CompletionStage<T> exceptionallyComposeAsync
+        (Function<Throwable, ? extends CompletionStage<T>> fn) {
+        return handle((r, ex) -> (ex == null)
+                      ? this
+                      : this.handleAsync((r1, ex1) -> fn.apply(ex1))
+                        .thenCompose(Function.identity()))
+            .thenCompose(Function.identity());
+    }
+
+    /**
+     * Returns a new CompletionStage that, when this stage completes
+     * exceptionally, is composed using the results of the supplied
+     * function applied to this stage's exception, using the
+     * supplied Executor.
+     *
+     * @implSpec The default implementation invokes {@link #handle},
+     * relaying to {@link #handleAsync} on exception, then {@link
+     * #thenCompose} for result.
+     *
+     * @param fn the function to use to compute the returned
+     * CompletionStage if this CompletionStage completed exceptionally
+     * @param executor the executor to use for asynchronous execution
+     * @return the new CompletionStage
+     * @since 12
+     */
+    public default CompletionStage<T> exceptionallyComposeAsync
+        (Function<Throwable, ? extends CompletionStage<T>> fn,
+         Executor executor) {
+        return handle((r, ex) -> (ex == null)
+                      ? this
+                      : this.handleAsync((r1, ex1) -> fn.apply(ex1), executor)
+                        .thenCompose(Function.identity()))
+            .thenCompose(Function.identity());
+    }
+
     /**
      * Returns a {@link CompletableFuture} maintaining the same
      * completion properties as this stage. If this stage is already a