Reduce Subscription Object Allocation

- significant reduction in object allocations
- details on research available at ReactiveX#1204

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

@@ -15,6 +15,7 @@
  */
 package rx;
 
+import rx.subscriptions.SubscriptionList;
 import rx.subscriptions.CompositeSubscription;
 
 /**
@@ -30,17 +31,23 @@
  */
 public abstract class Subscriber<T> implements Observer<T>, Subscription {
 
-    private final CompositeSubscription cs;
+    private final SubscriptionList cs;
 
-    protected Subscriber(CompositeSubscription cs) {
+    protected Subscriber(SubscriptionList cs) {
         if (cs == null) {
             throw new IllegalArgumentException("The CompositeSubscription can not be null");
         }
         this.cs = cs;
     }
+
+    @Deprecated
+    protected Subscriber(CompositeSubscription cs) {
+        this(new SubscriptionList());
+        add(cs);
+    }
 
     protected Subscriber() {
-        this(new CompositeSubscription());
+        this(new SubscriptionList());
     }
 
     protected Subscriber(Subscriber<?> op) {

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

@@ -27,7 +27,6 @@
 import rx.functions.Action0;
 import rx.functions.Func1;
 import rx.observables.GroupedObservable;
-import rx.subscriptions.CompositeSubscription;
 import rx.subscriptions.Subscriptions;
 
 /**
@@ -46,9 +45,9 @@ public OperatorGroupBy(final Func1<? super T, ? extends K> keySelector) {
 
     @Override
     public Subscriber<? super T> call(final Subscriber<? super GroupedObservable<K, T>> childObserver) {
-        // a new CompositeSubscription to decouple the subscription as the inner subscriptions need a separate lifecycle
+        // a new SubscriptionList to decouple the subscription as the inner subscriptions need a separate lifecycle
         // and will unsubscribe on this parent if they are all unsubscribed
-        return new Subscriber<T>(new CompositeSubscription()) {
+        return new Subscriber<T>() {
             private final Map<K, BufferUntilSubscriber<T>> groups = new HashMap<K, BufferUntilSubscriber<T>>();
             private final AtomicInteger completionCounter = new AtomicInteger(0);
             private final AtomicBoolean completionEmitted = new AtomicBoolean(false);

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

@@ -28,15 +28,15 @@
 import rx.Subscriber;
 import rx.functions.Action0;
 import rx.observables.GroupedObservable;
-import rx.subscriptions.CompositeSubscription;
+import rx.subscriptions.SubscriptionList;
 import rx.subscriptions.Subscriptions;
 
 public class OperatorPivot<K1, K2, T> implements Operator<GroupedObservable<K2, GroupedObservable<K1, T>>, GroupedObservable<K1, GroupedObservable<K2, T>>> {
 
     @Override
     public Subscriber<? super GroupedObservable<K1, GroupedObservable<K2, T>>> call(final Subscriber<? super GroupedObservable<K2, GroupedObservable<K1, T>>> child) {
         final AtomicReference<State> state = new AtomicReference<State>(State.create());
-        final OperatorPivot<K1, K2, T>.PivotSubscriber pivotSubscriber = new PivotSubscriber(new CompositeSubscription(), child, state);
+        final OperatorPivot<K1, K2, T>.PivotSubscriber pivotSubscriber = new PivotSubscriber(new SubscriptionList(), child, state);
         child.add(Subscriptions.create(new Action0() {
 
             @Override
@@ -65,12 +65,12 @@ private final class PivotSubscriber extends Subscriber<GroupedObservable<K1, Gro
          * needs to decouple the subscription as the inner subscriptions need a separate lifecycle
          * and will unsubscribe on this parent if they are all unsubscribed
          */
-        private final CompositeSubscription parentSubscription;
+        private final SubscriptionList parentSubscription;
         private final Subscriber<? super GroupedObservable<K2, GroupedObservable<K1, T>>> child;
         private final AtomicReference<State> state;
         private final GroupState<K1, K2, T> groups;
 
-        private PivotSubscriber(CompositeSubscription parentSubscription, Subscriber<? super GroupedObservable<K2, GroupedObservable<K1, T>>> child, AtomicReference<State> state) {
+        private PivotSubscriber(SubscriptionList parentSubscription, Subscriber<? super GroupedObservable<K2, GroupedObservable<K1, T>>> child, AtomicReference<State> state) {
             super(parentSubscription);
             this.parentSubscription = parentSubscription;
             this.child = child;
@@ -159,10 +159,10 @@ private static class GroupState<K1, K2, T> {
         private final ConcurrentHashMap<KeyPair<K1, K2>, Inner<K1, K2, T>> innerSubjects = new ConcurrentHashMap<KeyPair<K1, K2>, Inner<K1, K2, T>>();
         private final ConcurrentHashMap<K2, Outer<K1, K2, T>> outerSubjects = new ConcurrentHashMap<K2, Outer<K1, K2, T>>();
         private final AtomicBoolean completeEmitted = new AtomicBoolean();
-        private final CompositeSubscription parentSubscription;
+        private final SubscriptionList parentSubscription;
         private final Subscriber<? super GroupedObservable<K2, GroupedObservable<K1, T>>> child;
 
-        public GroupState(CompositeSubscription parentSubscription, Subscriber<? super GroupedObservable<K2, GroupedObservable<K1, T>>> child) {
+        public GroupState(SubscriptionList parentSubscription, Subscriber<? super GroupedObservable<K2, GroupedObservable<K1, T>>> child) {
             this.parentSubscription = parentSubscription;
             this.child = child;
         }

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

@@ -17,7 +17,7 @@
 
 import rx.Observable.Operator;
 import rx.Subscriber;
-import rx.subscriptions.CompositeSubscription;
+import rx.subscriptions.SubscriptionList;
 
 /**
  * Returns an Observable that emits the first <code>num</code> items emitted by the source
@@ -40,7 +40,7 @@ public OperatorTake(int limit) {
 
     @Override
     public Subscriber<? super T> call(final Subscriber<? super T> child) {
-        final CompositeSubscription parent = new CompositeSubscription();
+        final SubscriptionList parent = new SubscriptionList();
         if (limit == 0) {
             child.onCompleted();
             parent.unsubscribe();

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

@@ -19,7 +19,7 @@
 import rx.Scheduler;
 import rx.Subscriber;
 import rx.functions.Action0;
-import rx.subscriptions.CompositeSubscription;
+import rx.subscriptions.SubscriptionList;
 import rx.subscriptions.Subscriptions;
 
 /**
@@ -36,7 +36,7 @@ public OperatorUnsubscribeOn(Scheduler scheduler) {
 
     @Override
     public Subscriber<? super T> call(final Subscriber<? super T> subscriber) {
-        final CompositeSubscription parentSubscription = new CompositeSubscription();
+        final SubscriptionList parentSubscription = new SubscriptionList();
         subscriber.add(Subscriptions.create(new Action0() {
 
             @Override

rxjava-core/src/main/java/rx/subscriptions/CompositeSubscription.java

@@ -16,8 +16,11 @@
 package rx.subscriptions;
 
 import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.Collection;
+import java.util.HashSet;
 import java.util.List;
-import java.util.concurrent.atomic.AtomicReference;
+import java.util.Set;
 
 import rx.Subscription;
 import rx.exceptions.CompositeException;
@@ -30,154 +33,94 @@
  */
 public final class CompositeSubscription implements Subscription {
 
-    private final AtomicReference<State> state = new AtomicReference<State>();
-
-    /** Empty initial state. */
-    private static final State CLEAR_STATE;
-    /** Unsubscribed empty state. */
-    private static final State CLEAR_STATE_UNSUBSCRIBED;
-    static {
-        Subscription[] s0 = new Subscription[0];
-        CLEAR_STATE = new State(false, s0);
-        CLEAR_STATE_UNSUBSCRIBED = new State(true, s0);
-    }
-
-    private static final class State {
-        final boolean isUnsubscribed;
-        final Subscription[] subscriptions;
-
-        State(boolean u, Subscription[] s) {
-            this.isUnsubscribed = u;
-            this.subscriptions = s;
-        }
-
-        State unsubscribe() {
-            return CLEAR_STATE_UNSUBSCRIBED;
-        }
-
-        State add(Subscription s) {
-            int idx = subscriptions.length;
-            Subscription[] newSubscriptions = new Subscription[idx + 1];
-            System.arraycopy(subscriptions, 0, newSubscriptions, 0, idx);
-            newSubscriptions[idx] = s;
-            return new State(isUnsubscribed, newSubscriptions);
-        }
-
-        State remove(Subscription s) {
-            if ((subscriptions.length == 1 && subscriptions[0].equals(s)) || subscriptions.length == 0) {
-                return clear();
-            }
-            Subscription[] newSubscriptions = new Subscription[subscriptions.length - 1];
-            int idx = 0;
-            for (Subscription _s : subscriptions) {
-                if (!_s.equals(s)) {
-                    // was not in this composite
-                    if (idx == newSubscriptions.length) {
-                        return this;
-                    }
-                    newSubscriptions[idx] = _s;
-                    idx++;
-                }
-            }
-            if (idx == 0) {
-                return clear();
-            }
-            // subscription appeared more than once
-            if (idx < newSubscriptions.length) {
-                Subscription[] newSub2 = new Subscription[idx];
-                System.arraycopy(newSubscriptions, 0, newSub2, 0, idx);
-                return new State(isUnsubscribed, newSub2);
-            }
-            return new State(isUnsubscribed, newSubscriptions);
-        }
-
-        State clear() {
-            return isUnsubscribed ? CLEAR_STATE_UNSUBSCRIBED : CLEAR_STATE;
-        }
-    }
+    private Set<Subscription> subscriptions;
+    private boolean unsubscribed = false;
 
     public CompositeSubscription() {
-        state.set(CLEAR_STATE);
     }
 
     public CompositeSubscription(final Subscription... subscriptions) {
-        state.set(new State(false, subscriptions));
+        this.subscriptions = new HashSet<Subscription>(Arrays.asList(subscriptions));
     }
 
     @Override
-    public boolean isUnsubscribed() {
-        return state.get().isUnsubscribed;
+    public synchronized boolean isUnsubscribed() {
+        return unsubscribed;
     }
 
     public void add(final Subscription s) {
-        State oldState;
-        State newState;
-        do {
-            oldState = state.get();
-            if (oldState.isUnsubscribed) {
-                s.unsubscribe();
-                return;
+        Subscription unsubscribe = null;
+        synchronized (this) {
+            if (unsubscribed) {
+                unsubscribe = s;
             } else {
-                newState = oldState.add(s);
+                if (subscriptions == null) {
+                    subscriptions = new HashSet<Subscription>(4);
+                }
+                subscriptions.add(s);
             }
-        } while (!state.compareAndSet(oldState, newState));
+        }
+        if (unsubscribe != null) {
+            // call after leaving the synchronized block so we're not holding a lock while executing this
+            unsubscribe.unsubscribe();
+        }
     }
 
     public void remove(final Subscription s) {
-        State oldState;
-        State newState;
-        do {
-            oldState = state.get();
-            if (oldState.isUnsubscribed) {
+        boolean unsubscribe = false;
+        synchronized (this) {
+            if (unsubscribed || subscriptions == null) {
                 return;
-            } else {
-                newState = oldState.remove(s);
             }
-        } while (!state.compareAndSet(oldState, newState));
-        // if we removed successfully we then need to call unsubscribe on it
-        s.unsubscribe();
+            unsubscribe = subscriptions.remove(s);
+        }
+        if (unsubscribe) {
+            // if we removed successfully we then need to call unsubscribe on it (outside of the lock)
+            s.unsubscribe();
+        }
     }
 
     public void clear() {
-        State oldState;
-        State newState;
-        do {
-            oldState = state.get();
-            if (oldState.isUnsubscribed) {
+        Collection<Subscription> unsubscribe = null;
+        synchronized (this) {
+            if (unsubscribed || subscriptions == null) {
                 return;
             } else {
-                newState = oldState.clear();
+                unsubscribe = subscriptions;
+                subscriptions = null;
             }
-        } while (!state.compareAndSet(oldState, newState));
-        // if we cleared successfully we then need to call unsubscribe on all previous
-        unsubscribeFromAll(oldState.subscriptions);
+        }
+        unsubscribeFromAll(unsubscribe);
     }
 
     @Override
     public void unsubscribe() {
-        State oldState;
-        State newState;
-        do {
-            oldState = state.get();
-            if (oldState.isUnsubscribed) {
+        synchronized (this) {
+            if (unsubscribed) {
                 return;
-            } else {
-                newState = oldState.unsubscribe();
             }
-        } while (!state.compareAndSet(oldState, newState));
-        unsubscribeFromAll(oldState.subscriptions);
+            unsubscribed = true;
+        }
+        // we will only get here once
+        unsubscribeFromAll(subscriptions);
     }
 
-    private static void unsubscribeFromAll(Subscription[] subscriptions) {
-        final List<Throwable> es = new ArrayList<Throwable>();
+    private static void unsubscribeFromAll(Collection<Subscription> subscriptions) {
+        if (subscriptions == null) {
+            return;
+        }
+        List<Throwable> es = null;
         for (Subscription s : subscriptions) {
             try {
                 s.unsubscribe();
             } catch (Throwable e) {
+                if (es == null) {
+                    es = new ArrayList<Throwable>();
+                }
                 es.add(e);
             }
         }
-        if (!es.isEmpty()) {
+        if (es != null) {
             if (es.size() == 1) {
                 Throwable t = es.get(0);
                 if (t instanceof RuntimeException) {