2.x: Add Completable.fromRunnable() (#4629)

src/main/java/io/reactivex/Completable.java

@@ -339,6 +339,23 @@ public static Completable fromFuture(final Future<?> future) {
         return fromAction(Functions.futureAction(future));
     }
 
+    /**
+     * Returns a Completable instance that runs the given Runnable for each subscriber and
+     * emits either its exception or simply completes.
+     * <dl>
+     *  <dt><b>Scheduler:</b></dt>
+     *  <dd>{@code fromRunnable} does not operate by default on a particular {@link Scheduler}.</dd>
+     * </dl>
+     * @param run the runnable to run for each subscriber
+     * @return the new Completable instance
+     * @throws NullPointerException if run is null
+     */
+    @SchedulerSupport(SchedulerSupport.NONE)
+    public static Completable fromRunnable(final Runnable run) {
+        ObjectHelper.requireNonNull(run, "run is null");
+        return RxJavaPlugins.onAssembly(new CompletableFromRunnable(run));
+    }
+
     /**
      * Returns a Completable instance that subscribes to the given Observable, ignores all values and
      * emits only the terminal event.

src/main/java/io/reactivex/internal/operators/completable/CompletableFromRunnable.java

@@ -0,0 +1,47 @@
+/**
+ * Copyright 2016 Netflix, Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in
+ * compliance with the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software distributed under the License is
+ * distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See
+ * the License for the specific language governing permissions and limitations under the License.
+ */
+
+package io.reactivex.internal.operators.completable;
+
+import io.reactivex.Completable;
+import io.reactivex.CompletableObserver;
+import io.reactivex.disposables.Disposable;
+import io.reactivex.disposables.Disposables;
+import io.reactivex.exceptions.Exceptions;
+
+public final class CompletableFromRunnable extends Completable {
+
+    final Runnable runnable;
+
+    public CompletableFromRunnable(Runnable runnable) {
+        this.runnable = runnable;
+    }
+
+    @Override
+    protected void subscribeActual(CompletableObserver s) {
+        Disposable d = Disposables.empty();
+        s.onSubscribe(d);
+        try {
+            runnable.run();
+        } catch (Throwable e) {
+            Exceptions.throwIfFatal(e);
+            if (!d.isDisposed()) {
+                s.onError(e);
+            }
+            return;
+        }
+        if (!d.isDisposed()) {
+            s.onComplete();
+        }
+    }
+}

src/test/java/io/reactivex/completable/CompletableTest.java

@@ -4473,6 +4473,37 @@ public void run() {
         }
     }
 
+    @Test(expected = NullPointerException.class)
+    public void fromRunnableNull() {
+        Completable.fromRunnable(null);
+    }
+
+    @Test(timeout = 1000)
+    public void fromRunnableNormal() {
+        final AtomicInteger calls = new AtomicInteger();
+
+        Completable c = Completable.fromRunnable(new Runnable() {
+            @Override
+            public void run() {
+                calls.getAndIncrement();
+            }
+        });
+
+        c.blockingAwait();
+
+        Assert.assertEquals(1, calls.get());
+    }
+
+    @Test(timeout = 1000, expected = TestException.class)
+    public void fromRunnableThrows() {
+        Completable c = Completable.fromRunnable(new Runnable() {
+            @Override
+            public void run() { throw new TestException(); }
+        });
+
+        c.blockingAwait();
+    }
+
     @Test(expected = NullPointerException.class)
     public void doOnErrorNullValue() {
         Completable.complete().doOnError(null);