1.x: fix and deprecate evicting groupBy and add new overload

build.gradle

@@ -26,7 +26,7 @@ dependencies {
 
     testCompile 'junit:junit:4.12'
     testCompile 'org.mockito:mockito-core:1.10.19'
-    testCompile 'com.google.guava:guava:19.0'
+    testCompile 'com.google.guava:guava:24.0-jre'
     testCompile 'com.pushtorefresh.java-private-constructor-checker:checker:1.2.0'
 
     perfCompile 'org.openjdk.jmh:jmh-core:1.11.3'

src/main/java/rx/Observable.java

@@ -7275,7 +7275,7 @@ public final void forEach(final Action1<? super T> onNext, final Action1<Throwab
      * @see <a href="http://reactivex.io/documentation/operators/groupby.html">ReactiveX operators documentation: GroupBy</a>
      */
     public final <K, R> Observable<GroupedObservable<K, R>> groupBy(final Func1<? super T, ? extends K> keySelector, final Func1<? super T, ? extends R> elementSelector) {
-        return lift(new OperatorGroupBy<T, K, R>(keySelector, elementSelector));
+        return lift(new OperatorGroupByEvicting<T, K, R>(keySelector, elementSelector));
     }
 
     /**
@@ -7334,7 +7334,12 @@ public final <K, R> Observable<GroupedObservable<K, R>> groupBy(final Func1<? su
      *             if {@code evictingMapFactory} is null
      * @see <a href="http://reactivex.io/documentation/operators/groupby.html">ReactiveX operators documentation: GroupBy</a>
      * @since 1.3
+     * @deprecated since 1.3.7, use {@link #groupBy(Func1, Func1, int, boolean, Func1)} 
+     *             instead which uses much less memory. Please take note of the 
+     *             usage difference involving the evicting action which now expects
+     *             the value from the map instead of the key.
      */
+    @Deprecated
     public final <K, R> Observable<GroupedObservable<K, R>> groupBy(final Func1<? super T, ? extends K> keySelector,
             final Func1<? super T, ? extends R> elementSelector, final Func1<Action1<K>, Map<K, Object>> evictingMapFactory) {
         if (evictingMapFactory == null) {
@@ -7369,6 +7374,72 @@ public final <K, R> Observable<GroupedObservable<K, R>> groupBy(final Func1<? su
      *
      * @param keySelector
      *            a function that extracts the key for each item
+     * @param elementSelector
+     *            a function that extracts the return element for each item
+     * @param bufferSize 
+     *            the size of the buffer ({@link RxRingBuffer.SIZE} may be suitable).
+     * @param delayError
+     *            if and only if false then onError emissions can shortcut onNext emissions (emissions may be buffered)
+     * @param evictingMapFactory
+     *            a function that given an eviction action returns a {@link Map} instance that will be used to assign 
+     *            items to the appropriate {@code GroupedObservable}s. The {@code Map} instance must be thread-safe 
+     *            and any eviction must trigger a call to the supplied action (synchronously or asynchronously). 
+     *            This can be used to limit the size of the map by evicting entries by map maximum size or access time for 
+     *            instance. Here's an example using Guava's {@code CacheBuilder} from v24.0:
+     *            <pre>
+     *            {@code
+     *            Func1<Action1<Object>, Map<K, Object>> mapFactory 
+     *              = action -> CacheBuilder.newBuilder()
+     *                  .maximumSize(1000)
+     *                  .expireAfterAccess(12, TimeUnit.HOURS)
+     *                  .removalListener(entry -> action.call(entry.getValue()))
+     *                  .<K, Object> build().asMap();
+     *            }
+     *            </pre>
+     *            
+     * @param <K>
+     *            the key type
+     * @param <R>
+     *            the element type
+     * @return an {@code Observable} that emits {@link GroupedObservable}s, each of which corresponds to a
+     *         unique key value and each of which emits those items from the source Observable that share that
+     *         key value
+     * @throws NullPointerException
+     *             if {@code evictingMapFactory} is null
+     * @see <a href="http://reactivex.io/documentation/operators/groupby.html">ReactiveX operators documentation: GroupBy</a>
+     * @since 1.3.7
+     */
+    @Experimental
+    public final <K, R> Observable<GroupedObservable<K, R>> groupBy(final Func1<? super T, ? extends K> keySelector, 
+            final Func1<? super T, ? extends R> elementSelector, int bufferSize, boolean delayError, 
+            final Func1<Action1<Object>, Map<K, Object>> evictingMapFactory) {
+        if (evictingMapFactory == null) {
+            throw new NullPointerException("evictingMapFactory cannot be null");
+        }
+        return lift(new OperatorGroupByEvicting<T, K, R>(
+                keySelector, elementSelector, bufferSize, delayError, evictingMapFactory));
+    }
+
+    /**
+     * Groups the items emitted by an {@code Observable} according to a specified criterion, and emits these
+     * grouped items as {@link GroupedObservable}s. The emitted {@code GroupedObservable} allows only a single 
+     * {@link Subscriber} during its lifetime and if this {@code Subscriber} unsubscribes before the 
+     * source terminates, the next emission by the source having the same key will trigger a new 
+     * {@code GroupedObservable} emission.
+     * <p>
+     * <img width="640" height="360" src="https://raw.github.com/wiki/ReactiveX/RxJava/images/rx-operators/groupBy.png" alt="">
+     * <p>
+     * <em>Note:</em> A {@link GroupedObservable} will cache the items it is to emit until such time as it
+     * is subscribed to. For this reason, in order to avoid memory leaks, you should not simply ignore those
+     * {@code GroupedObservable}s that do not concern you. Instead, you can signal to them that they may
+     * discard their buffers by applying an operator like {@link #ignoreElements} to them.
+     * <dl>
+     *  <dt><b>Scheduler:</b></dt>
+     *  <dd>{@code groupBy} does not operate by default on a particular {@link Scheduler}.</dd>
+     * </dl>
+     * 
+     * @param keySelector
+     *            a function that extracts the key for each item
      * @param <K>
      *            the key type
      * @return an {@code Observable} that emits {@link GroupedObservable}s, each of which corresponds to a
@@ -7377,7 +7448,7 @@ public final <K, R> Observable<GroupedObservable<K, R>> groupBy(final Func1<? su
      * @see <a href="http://reactivex.io/documentation/operators/groupby.html">ReactiveX operators documentation: GroupBy</a>
      */
     public final <K> Observable<GroupedObservable<K, T>> groupBy(final Func1<? super T, ? extends K> keySelector) {
-        return lift(new OperatorGroupBy<T, K, T>(keySelector));
+        return lift(new OperatorGroupByEvicting<T, K, T>(keySelector));
     }
 
     /**

src/main/java/rx/internal/operators/OperatorGroupBy.java

@@ -42,13 +42,16 @@
  *            the source and group value type
  * @param <V>
  *            the value type of the groups
+ * @deprecated 
+ *            since 1.3.7, use {@link OperatorGroupByEvicting} instead
  */
+@Deprecated
 public final class OperatorGroupBy<T, K, V> implements Operator<GroupedObservable<K, V>, T> {
     final Func1<? super T, ? extends K> keySelector;
     final Func1<? super T, ? extends V> valueSelector;
     final int bufferSize;
     final boolean delayError;
-    final Func1<Action1<K>, Map<K, Object>> mapFactory;
+    final Func1<Action1<K>, Map<K, Object>> mapFactory; //nullable
 
     @SuppressWarnings({ "unchecked", "rawtypes" })
     public OperatorGroupBy(Func1<? super T, ? extends K> keySelector) {
@@ -116,6 +119,10 @@ public static final class GroupBySubscriber<T, K, V>
         final int bufferSize;
         final boolean delayError;
         final Map<Object, GroupedUnicast<K, V>> groups;
+
+        // double store the groups to workaround the bug in the 
+        // signature of groupBy with evicting map factory
+        final Map<Object, GroupedUnicast<K, V>> groupsCopy;
         final Queue<GroupedObservable<K, V>> queue;
         final GroupByProducer producer;
         final Queue<K> evictedKeys;
@@ -134,7 +141,7 @@ public static final class GroupBySubscriber<T, K, V>
         volatile boolean done;
 
         final AtomicInteger wip;
-
+        
         public GroupBySubscriber(Subscriber<? super GroupedObservable<K, V>> actual, Func1<? super T, ? extends K> keySelector,
                 Func1<? super T, ? extends V> valueSelector, int bufferSize, boolean delayError,
                 Func1<Action1<K>, Map<K, Object>> mapFactory) {
@@ -158,6 +165,7 @@ public GroupBySubscriber(Subscriber<? super GroupedObservable<K, V>> actual, Fun
                 this.evictedKeys = new ConcurrentLinkedQueue<K>();
                 this.groups = createMap(mapFactory, new EvictionAction<K>(evictedKeys));
             }
+            this.groupsCopy = new ConcurrentHashMap<Object, GroupedUnicast<K, V>>();
         }
 
         static class EvictionAction<K> implements Action1<K> {
@@ -211,6 +219,9 @@ public void onNext(T t) {
                 if (!cancelled.get()) {
                     group = GroupedUnicast.createWith(key, bufferSize, this, delayError);
                     groups.put(mapKey, group);
+                    if (evictedKeys != null) {
+                        groupsCopy.put(mapKey, group);
+                    }
 
                     groupCount.getAndIncrement();
 
@@ -234,7 +245,9 @@ public void onNext(T t) {
             if (evictedKeys != null) {
                 K evictedKey;
                 while ((evictedKey = evictedKeys.poll()) != null) {
-                    GroupedUnicast<K, V> g = groups.get(evictedKey);
+                    GroupedUnicast<K, V> g = groupsCopy.remove(evictedKey);
+                    // do a null check on g because cancel(K) could have cleared
+                    // the map
                     if (g != null) {
                         g.onComplete();
                     }
@@ -270,6 +283,7 @@ public void onCompleted() {
             }
             groups.clear();
             if (evictedKeys != null) {
+                groupsCopy.clear();
                 evictedKeys.clear();
             }
 
@@ -304,6 +318,9 @@ public void cancel(K key) {
                     unsubscribe();
                 }
             }
+            if (evictedKeys != null) {
+                groupsCopy.remove(mapKey);
+            }
         }
 
         void drain() {
@@ -364,6 +381,7 @@ void errorAll(Subscriber<? super GroupedObservable<K, V>> a, Queue<?> q, Throwab
             List<GroupedUnicast<K, V>> list = new ArrayList<GroupedUnicast<K, V>>(groups.values());
             groups.clear();
             if (evictedKeys != null) {
+                groupsCopy.clear();
                 evictedKeys.clear();
             }