Delay with subscription and item delaying observables.

Author: akarnokd

rxjava-core/src/main/java/rx/Observable.java

@@ -2167,6 +2167,50 @@ public static Observable<Long> timer(long initialDelay, long period, TimeUnit un
         return create(new OperationTimer.TimerPeriodically(initialDelay, period, unit, scheduler));
     }
 
+    /**
+     * Create an Observable which delays the events via another Observable on a per item-basis.
+     * <p>
+     * Note: onError or onCompleted events are immediately propagated.
+     * <p>
+     * Note: if the Observable returned by the {@code itemDelay} just completes, that
+     * particular source item is not emitted.
+     * 
+     * @param <U> the item delay value type (ignored)
+     * @param itemDelay function that returns an Observable for each source item which is
+     *                  then used for delaying that particular item until the Observable
+     *                  fires its first onNext event.
+     * @return an Observable which delays the events via another Observable on a per item-basis.
+     */
+    public <U> Observable<T> delay(Func1<? super T, ? extends Observable<U>> itemDelay) {
+        return create(OperationDelay.delay(this, itemDelay));
+    }
+    /**
+     * Create an Observable which delays the subscription and events via another Observables on a per item-basis.
+     * <p>
+     * Note: onError or onCompleted events are immediately propagated.
+     * <p>
+     * Note: if the Observable returned by the {@code itemDelay} just completes, that
+     * particular source item is not emitted.
+     * <p>
+     * Note: if the {@code subscriptionDelay}'s Observable just completes, the created
+     * observable will just complete as well.
+     * 
+     * @param <U> the subscription delay value type (ignored)
+     * @param <V> the item delay value type (ignored)
+     * @param subscriptionDelay function that returns an Observable which will trigger
+     *                          the subscription to the source observable once it fires an
+     *                          onNext event.
+     * @param itemDelay function that returns an Observable for each source item which is
+     *                  then used for delaying that particular item until the Observable
+     *                  fires its first onNext event.
+     * @return an Observable which delays the events via another Observable on a per item-basis.
+     */
+    public <U, V> Observable<T> delay(
+            Func0<? extends Observable<U>> subscriptionDelay,
+            Func1<? super T, ? extends Observable<V>> itemDelay) {
+        return create(OperationDelay.delay(this, subscriptionDelay, itemDelay));
+    }
+    
     /**
      * Returns an Observable that emits the items emitted by the source
      * Observable shifted forward in time by a specified delay. Error

rxjava-core/src/main/java/rx/operators/OperationDelay.java

@@ -23,8 +23,11 @@
 import rx.Scheduler;
 import rx.Subscription;
 import rx.observables.ConnectableObservable;
+import rx.subscriptions.CompositeSubscription;
 import rx.subscriptions.SerialSubscription;
+import rx.subscriptions.Subscriptions;
 import rx.util.functions.Action0;
+import rx.util.functions.Func0;
 import rx.util.functions.Func1;
 
 public final class OperationDelay {
@@ -82,4 +85,196 @@ public void call() {
             return ssub;
         }
     }
+    /**
+     * Delay the emission of the source items by a per-item observable that fires its first element.
+     */
+    public static <T, U> OnSubscribeFunc<T> delay(Observable<? extends T> source, 
+            Func1<? super T, ? extends Observable<U>> itemDelay) {
+        return new DelayViaObservable<T, Object, U>(source, null, itemDelay);
+    }
+    /**
+     * Delay the subscription and emission of the source items by a per-item observable that fires its first element.
+     */
+    public static <T, U, V> OnSubscribeFunc<T> delay(Observable<? extends T> source, 
+            Func0<? extends Observable<U>> subscriptionDelay,
+            Func1<? super T, ? extends Observable<V>> itemDelay) {
+        return new DelayViaObservable<T, U, V>(source, subscriptionDelay, itemDelay);
+    }
+    /**
+     * Delay the emission of the source items by a per-item observable that fires its first element.
+     */
+    private static final class DelayViaObservable<T, U, V> implements OnSubscribeFunc<T> {
+        final Observable<? extends T> source;
+        final Func0<? extends Observable<U>> subscriptionDelay;
+        final Func1<? super T, ? extends Observable<V>> itemDelay;
+
+        public DelayViaObservable(Observable<? extends T> source, 
+                Func0<? extends Observable<U>> subscriptionDelay,
+                Func1<? super T, ? extends Observable<V>> itemDelay) {
+            this.source = source;
+            this.subscriptionDelay = subscriptionDelay;
+            this.itemDelay = itemDelay;
+        }
+
+        @Override
+        public Subscription onSubscribe(Observer<? super T> t1) {
+            CompositeSubscription csub = new CompositeSubscription();
+            
+            if (subscriptionDelay == null) {
+                csub.add(source.subscribe(new SourceObserver<T, V>(t1, itemDelay, csub)));
+            } else {
+                Observable<U> subscriptionSource;
+                try {
+                    subscriptionSource = subscriptionDelay.call();
+                } catch (Throwable t) {
+                    t1.onError(t);
+                    return Subscriptions.empty();
+                }
+                SerialSubscription ssub = new SerialSubscription();
+                csub.add(ssub);
+                ssub.set(subscriptionSource.subscribe(new SubscribeDelay<T, U, V>(source, t1, itemDelay, csub, ssub)));
+            }
+            
+            return csub;
+        }
+        private static final class SubscribeDelay<T, U, V> implements Observer<U> {
+            final Observable<? extends T> source;
+            final Observer<? super T> observer;
+            final Func1<? super T, ? extends Observable<V>> itemDelay;
+            final CompositeSubscription csub;
+            final Subscription self;
+            /** Prevent any onError and onCompleted once the first item was delivered. */
+            boolean subscribed;
+
+            public SubscribeDelay(Observable<? extends T> source, Observer<? super T> observer, Func1<? super T, ? extends Observable<V>> itemDelay, 
+                    CompositeSubscription csub, Subscription self) {
+                this.source = source;
+                this.observer = observer;
+                this.itemDelay = itemDelay;
+                this.csub = csub;
+                this.self = self;
+            }
+
+            @Override
+            public void onNext(U args) {
+                subscribed = true;
+                csub.remove(self);
+                csub.add(source.subscribe(new SourceObserver<T, V>(observer, itemDelay, csub)));
+            }
+
+            @Override
+            public void onError(Throwable e) {
+                if (!subscribed) {
+                    observer.onError(e);
+                    csub.unsubscribe();
+                }
+            }
+
+            @Override
+            public void onCompleted() {
+                if (!subscribed) {
+                    observer.onCompleted();
+                    csub.unsubscribe();
+                }
+            }
+        }
+        /** The source observer. */
+        private static final class SourceObserver<T, U> implements Observer<T> {
+            final Observer<? super T> observer;
+            final Func1<? super T, ? extends Observable<U>> itemDelay;
+            final CompositeSubscription csub;
+            /** Guard to avoid overlapping events from the various sources. */
+            final Object guard;
+            boolean done;
+
+            public SourceObserver(Observer<? super T> observer, Func1<? super T, ? extends Observable<U>> itemDelay, CompositeSubscription csub) {
+                this.observer = observer;
+                this.itemDelay = itemDelay;
+                this.csub = csub;
+                this.guard = new Object();
+            }
+
+            @Override
+            public void onNext(T args) {
+                Observable<U> delayer;
+                try {
+                    delayer = itemDelay.call(args);
+                } catch (Throwable t) {
+                    onError(t);
+                    return;
+                }
+                SerialSubscription ssub = new SerialSubscription();
+                csub.add(ssub);
+                
+                ssub.set(delayer.subscribe(new DelayObserver<T, U>(args, this, ssub)));
+            }
+
+            @Override
+            public void onError(Throwable e) {
+                synchronized (guard) {
+                    if (done) {
+                        return;
+                    }
+                    done = true;
+                    observer.onError(e);
+                }
+                csub.unsubscribe();
+            }
+
+            @Override
+            public void onCompleted() {
+                synchronized (guard) {
+                    if (done) {
+                        return;
+                    }
+                    done = true;
+                    observer.onCompleted();
+                }
+                csub.unsubscribe();
+            }
+            
+            public void emit(T value, Subscription token) {
+                synchronized (guard) {
+                    if (done) {
+                        return;
+                    }
+                    observer.onNext(value);
+                }
+                remove(token);
+            }
+            public void remove(Subscription token) {
+                csub.remove(token);
+            }
+        }
+        /**
+         * Delay observer.
+         */
+        private static final class DelayObserver<T, U> implements Observer<U> {
+            final T value;
+            final SourceObserver<T, U> parent;
+            final Subscription token;
+
+            public DelayObserver(T value, SourceObserver<T, U> parent, Subscription token) {
+                this.value = value;
+                this.parent = parent;
+                this.token = token;
+            }
+
+            @Override
+            public void onNext(U args) {
+                parent.emit(value, token);
+            }
+
+            @Override
+            public void onError(Throwable e) {
+                parent.onError(e);
+            }
+
+            @Override
+            public void onCompleted() {
+                parent.remove(token);
+            }
+            
+        }
+    }
 }