2.x: Add Observable switchMapX and concatMapX operators (#5875)

* 2.x: Add Observable switchMapX and concatMapX operators

* Rename local variables to match their datatype better.

src/main/java/io/reactivex/internal/operators/mixed/FlowableConcatMapSingle.java

@@ -255,10 +255,10 @@ void drain() {
                             consumed = c;
                         }
 
-                        SingleSource<? extends R> ms;
+                        SingleSource<? extends R> ss;
 
                         try {
-                            ms = ObjectHelper.requireNonNull(mapper.apply(v), "The mapper returned a null SingleSource");
+                            ss = ObjectHelper.requireNonNull(mapper.apply(v), "The mapper returned a null SingleSource");
                         } catch (Throwable ex) {
                             Exceptions.throwIfFatal(ex);
                             upstream.cancel();
@@ -270,7 +270,7 @@ void drain() {
                         }
 
                         state = STATE_ACTIVE;
-                        ms.subscribe(inner);
+                        ss.subscribe(inner);
                         break;
                     } else if (s == STATE_RESULT_VALUE) {
                         long e = emitted;

src/main/java/io/reactivex/internal/operators/mixed/FlowableSwitchMapSingle.java

@@ -115,10 +115,10 @@ public void onNext(T t) {
                 current.dispose();
             }
 
-            SingleSource<? extends R> ms;
+            SingleSource<? extends R> ss;
 
             try {
-                ms = ObjectHelper.requireNonNull(mapper.apply(t), "The mapper returned a null SingleSource");
+                ss = ObjectHelper.requireNonNull(mapper.apply(t), "The mapper returned a null SingleSource");
             } catch (Throwable ex) {
                 Exceptions.throwIfFatal(ex);
                 upstream.cancel();
@@ -135,7 +135,7 @@ public void onNext(T t) {
                     break;
                 }
                 if (inner.compareAndSet(current, observer)) {
-                    ms.subscribe(observer);
+                    ss.subscribe(observer);
                     break;
                 }
             }

src/main/java/io/reactivex/internal/operators/mixed/ObservableConcatMapCompletable.java

@@ -0,0 +1,277 @@
+/**
+ * Copyright (c) 2016-present, RxJava Contributors.
+ *
+ * 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.mixed;
+
+import java.util.concurrent.atomic.*;
+
+import io.reactivex.*;
+import io.reactivex.annotations.Experimental;
+import io.reactivex.disposables.Disposable;
+import io.reactivex.exceptions.*;
+import io.reactivex.functions.Function;
+import io.reactivex.internal.disposables.DisposableHelper;
+import io.reactivex.internal.functions.ObjectHelper;
+import io.reactivex.internal.fuseable.SimplePlainQueue;
+import io.reactivex.internal.queue.SpscLinkedArrayQueue;
+import io.reactivex.internal.util.*;
+import io.reactivex.plugins.RxJavaPlugins;
+
+/**
+ * Maps the upstream intems into {@link CompletableSource}s and subscribes to them one after the
+ * other completes or terminates (in error-delaying mode).
+ * @param <T> the upstream value type
+ * @since 2.1.11 - experimental
+ */
+@Experimental
+public final class ObservableConcatMapCompletable<T> extends Completable {
+
+    final Observable<T> source;
+
+    final Function<? super T, ? extends CompletableSource> mapper;
+
+    final ErrorMode errorMode;
+
+    final int prefetch;
+
+    public ObservableConcatMapCompletable(Observable<T> source,
+            Function<? super T, ? extends CompletableSource> mapper,
+            ErrorMode errorMode,
+            int prefetch) {
+        this.source = source;
+        this.mapper = mapper;
+        this.errorMode = errorMode;
+        this.prefetch = prefetch;
+    }
+
+    @Override
+    protected void subscribeActual(CompletableObserver s) {
+        source.subscribe(new ConcatMapCompletableObserver<T>(s, mapper, errorMode, prefetch));
+    }
+
+    static final class ConcatMapCompletableObserver<T>
+    extends AtomicInteger
+    implements Observer<T>, Disposable {
+
+        private static final long serialVersionUID = 3610901111000061034L;
+
+        final CompletableObserver downstream;
+
+        final Function<? super T, ? extends CompletableSource> mapper;
+
+        final ErrorMode errorMode;
+
+        final AtomicThrowable errors;
+
+        final ConcatMapInnerObserver inner;
+
+        final int prefetch;
+
+        final SimplePlainQueue<T> queue;
+
+        Disposable upstream;
+
+        volatile boolean active;
+
+        volatile boolean done;
+
+        volatile boolean disposed;
+
+        ConcatMapCompletableObserver(CompletableObserver downstream,
+                Function<? super T, ? extends CompletableSource> mapper,
+                ErrorMode errorMode, int prefetch) {
+            this.downstream = downstream;
+            this.mapper = mapper;
+            this.errorMode = errorMode;
+            this.prefetch = prefetch;
+            this.errors = new AtomicThrowable();
+            this.inner = new ConcatMapInnerObserver(this);
+            this.queue = new SpscLinkedArrayQueue<T>(prefetch);
+        }
+
+        @Override
+        public void onSubscribe(Disposable s) {
+            if (DisposableHelper.validate(upstream, s)) {
+                this.upstream = s;
+                downstream.onSubscribe(this);
+            }
+        }
+
+        @Override
+        public void onNext(T t) {
+            queue.offer(t);
+            drain();
+        }
+
+        @Override
+        public void onError(Throwable t) {
+            if (errors.addThrowable(t)) {
+                if (errorMode == ErrorMode.IMMEDIATE) {
+                    disposed = true;
+                    inner.dispose();
+                    t = errors.terminate();
+                    if (t != ExceptionHelper.TERMINATED) {
+                        downstream.onError(t);
+                    }
+                    if (getAndIncrement() == 0) {
+                        queue.clear();
+                    }
+                } else {
+                    done = true;
+                    drain();
+                }
+            } else {
+                RxJavaPlugins.onError(t);
+            }
+        }
+
+        @Override
+        public void onComplete() {
+            done = true;
+            drain();
+        }
+
+        @Override
+        public void dispose() {
+            disposed = true;
+            upstream.dispose();
+            inner.dispose();
+            if (getAndIncrement() == 0) {
+                queue.clear();
+            }
+        }
+
+        @Override
+        public boolean isDisposed() {
+            return disposed;
+        }
+
+        void innerError(Throwable ex) {
+            if (errors.addThrowable(ex)) {
+                if (errorMode == ErrorMode.IMMEDIATE) {
+                    disposed = true;
+                    upstream.dispose();
+                    ex = errors.terminate();
+                    if (ex != ExceptionHelper.TERMINATED) {
+                        downstream.onError(ex);
+                    }
+                    if (getAndIncrement() == 0) {
+                        queue.clear();
+                    }
+                } else {
+                    active = false;
+                    drain();
+                }
+            } else {
+                RxJavaPlugins.onError(ex);
+            }
+        }
+
+        void innerComplete() {
+            active = false;
+            drain();
+        }
+
+        void drain() {
+            if (getAndIncrement() != 0) {
+                return;
+            }
+
+            do {
+                if (disposed) {
+                    queue.clear();
+                    return;
+                }
+
+                if (!active) {
+
+                    if (errorMode == ErrorMode.BOUNDARY) {
+                        if (errors.get() != null) {
+                            disposed = true;
+                            queue.clear();
+                            Throwable ex = errors.terminate();
+                            downstream.onError(ex);
+                            return;
+                        }
+                    }
+
+                    boolean d = done;
+                    T v = queue.poll();
+                    boolean empty = v == null;
+
+                    if (d && empty) {
+                        disposed = true;
+                        Throwable ex = errors.terminate();
+                        if (ex != null) {
+                            downstream.onError(ex);
+                        } else {
+                            downstream.onComplete();
+                        }
+                        return;
+                    }
+
+                    if (!empty) {
+
+                        CompletableSource cs;
+
+                        try {
+                            cs = ObjectHelper.requireNonNull(mapper.apply(v), "The mapper returned a null CompletableSource");
+                        } catch (Throwable ex) {
+                            Exceptions.throwIfFatal(ex);
+                            disposed = true;
+                            queue.clear();
+                            upstream.dispose();
+                            errors.addThrowable(ex);
+                            ex = errors.terminate();
+                            downstream.onError(ex);
+                            return;
+                        }
+                        active = true;
+                        cs.subscribe(inner);
+                    }
+                }
+            } while (decrementAndGet() != 0);
+        }
+
+        static final class ConcatMapInnerObserver extends AtomicReference<Disposable>
+        implements CompletableObserver {
+
+            private static final long serialVersionUID = 5638352172918776687L;
+
+            final ConcatMapCompletableObserver<?> parent;
+
+            ConcatMapInnerObserver(ConcatMapCompletableObserver<?> parent) {
+                this.parent = parent;
+            }
+
+            @Override
+            public void onSubscribe(Disposable d) {
+                DisposableHelper.replace(this, d);
+            }
+
+            @Override
+            public void onError(Throwable e) {
+                parent.innerError(e);
+            }
+
+            @Override
+            public void onComplete() {
+                parent.innerComplete();
+            }
+
+            void dispose() {
+                DisposableHelper.dispose(this);
+            }
+        }
+    }
+}