2.x: add subjects for Single, Maybe and Completable (#4967)

* 2.x: add subjects for Single, Maybe and Completable

* Add CheckReturnValue, rename local test vars

Author: akarnokd

src/main/java/io/reactivex/subjects/CompletableSubject.java

@@ -0,0 +1,229 @@
+/**
+ * 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.subjects;
+
+import java.util.concurrent.atomic.*;
+
+import io.reactivex.*;
+import io.reactivex.annotations.*;
+import io.reactivex.disposables.Disposable;
+import io.reactivex.plugins.RxJavaPlugins;
+
+/**
+ * Represents a hot Completable-like source and consumer of events similar to Subjects.
+ * <p>
+ * All methods are thread safe. Calling onComplete multiple
+ * times has no effect. Calling onError multiple times relays the Throwable to
+ * the RxJavaPlugins' error handler.
+ * <p>
+ * The CompletableSubject doesn't store the Disposables coming through onSubscribe but
+ * disposes them once the other onXXX methods were called (terminal state reached).
+ * @since 2.0.5 - experimental
+ */
+@Experimental
+public final class CompletableSubject extends Completable implements CompletableObserver {
+
+    final AtomicReference<CompletableDisposable[]> observers;
+
+    static final CompletableDisposable[] EMPTY = new CompletableDisposable[0];
+
+    static final CompletableDisposable[] TERMINATED = new CompletableDisposable[0];
+
+    final AtomicBoolean once;
+    Throwable error;
+
+    /**
+     * Creates a fresh CompletableSubject.
+     * @return the new CompletableSubject instance
+     */
+    @CheckReturnValue
+    public static CompletableSubject create() {
+        return new CompletableSubject();
+    }
+
+    CompletableSubject() {
+        once = new AtomicBoolean();
+        observers = new AtomicReference<CompletableDisposable[]>(EMPTY);
+    }
+
+    @Override
+    public void onSubscribe(Disposable d) {
+        if (observers.get() == TERMINATED) {
+            d.dispose();
+        }
+    }
+
+    @Override
+    public void onError(Throwable e) {
+        if (e == null) {
+            e = new NullPointerException("Null errors are not allowed in 2.x");
+        }
+        if (once.compareAndSet(false, true)) {
+            this.error = e;
+            for (CompletableDisposable md : observers.getAndSet(TERMINATED)) {
+                md.actual.onError(e);
+            }
+        } else {
+            RxJavaPlugins.onError(e);
+        }
+    }
+
+    @Override
+    public void onComplete() {
+        if (once.compareAndSet(false, true)) {
+            for (CompletableDisposable md : observers.getAndSet(TERMINATED)) {
+                md.actual.onComplete();
+            }
+        }
+    }
+
+    @Override
+    protected void subscribeActual(CompletableObserver observer) {
+        CompletableDisposable md = new CompletableDisposable(observer, this);
+        observer.onSubscribe(md);
+        if (add(md)) {
+            if (md.isDisposed()) {
+                remove(md);
+            }
+        } else {
+            Throwable ex = error;
+            if (ex != null) {
+                observer.onError(ex);
+            } else {
+                observer.onComplete();
+            }
+        }
+    }
+
+    boolean add(CompletableDisposable inner) {
+        for (;;) {
+            CompletableDisposable[] a = observers.get();
+            if (a == TERMINATED) {
+                return false;
+            }
+
+            int n = a.length;
+
+            CompletableDisposable[] b = new CompletableDisposable[n + 1];
+            System.arraycopy(a, 0, b, 0, n);
+            b[n] = inner;
+            if (observers.compareAndSet(a, b)) {
+                return true;
+            }
+        }
+    }
+
+    void remove(CompletableDisposable inner) {
+        for (;;) {
+            CompletableDisposable[] a = observers.get();
+            int n = a.length;
+            if (n == 0) {
+                return;
+            }
+
+            int j = -1;
+
+            for (int i = 0; i < n; i++) {
+                if (a[i] == inner) {
+                    j = i;
+                    break;
+                }
+            }
+
+            if (j < 0) {
+                return;
+            }
+            CompletableDisposable[] b;
+            if (n == 1) {
+                b = EMPTY;
+            } else {
+                b = new CompletableDisposable[n - 1];
+                System.arraycopy(a, 0, b, 0, j);
+                System.arraycopy(a, j + 1, b, j, n - j - 1);
+            }
+
+            if (observers.compareAndSet(a, b)) {
+                return;
+            }
+        }
+    }
+
+    /**
+     * Returns the terminal error if this CompletableSubject has been terminated with an error, null otherwise.
+     * @return the terminal error or null if not terminated or not with an error
+     */
+    public Throwable getThrowable() {
+        if (observers.get() == TERMINATED) {
+            return error;
+        }
+        return null;
+    }
+
+    /**
+     * Returns true if this CompletableSubject has been terminated with an error.
+     * @return true if this CompletableSubject has been terminated with an error
+     */
+    public boolean hasThrowable() {
+        return observers.get() == TERMINATED && error != null;
+    }
+
+    /**
+     * Returns true if this CompletableSubject has been completed.
+     * @return true if this CompletableSubject has been completed
+     */
+    public boolean hasComplete() {
+        return observers.get() == TERMINATED && error == null;
+    }
+
+    /**
+     * Returns true if this CompletableSubject has observers.
+     * @return true if this CompletableSubject has observers
+     */
+    public boolean hasObservers() {
+        return observers.get().length != 0;
+    }
+
+    /**
+     * Returns the number of current observers.
+     * @return the number of current observers
+     */
+    /* test */ int observerCount() {
+        return observers.get().length;
+    }
+
+    static final class CompletableDisposable
+    extends AtomicReference<CompletableSubject> implements Disposable {
+        private static final long serialVersionUID = -7650903191002190468L;
+
+        final CompletableObserver actual;
+
+        CompletableDisposable(CompletableObserver actual, CompletableSubject parent) {
+            this.actual = actual;
+            lazySet(parent);
+        }
+
+        @Override
+        public void dispose() {
+            CompletableSubject parent = getAndSet(null);
+            if (parent != null) {
+                parent.remove(this);
+            }
+        }
+
+        @Override
+        public boolean isDisposed() {
+            return get() == null;
+        }
+    }
+}