Merge pull request #1755 from benjchristensen/issue1688

OnSubscribeRefCount with Synchronous Support

Author: benjchristensen

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

@@ -15,195 +15,123 @@
  */
 package rx.internal.operators;
 
-import java.util.ArrayList;
-import java.util.List;
-import java.util.Map;
-import java.util.WeakHashMap;
+import java.util.concurrent.atomic.AtomicBoolean;
+import java.util.concurrent.atomic.AtomicInteger;
+import java.util.concurrent.locks.ReentrantLock;
+
 import rx.Observable.OnSubscribe;
 import rx.Subscriber;
 import rx.Subscription;
 import rx.functions.Action0;
+import rx.functions.Action1;
 import rx.observables.ConnectableObservable;
+import rx.subscriptions.CompositeSubscription;
 import rx.subscriptions.Subscriptions;
 
 /**
- * Returns an observable sequence that stays connected to the source as long
- * as there is at least one subscription to the observable sequence.
- * @param <T> the value type
+ * Returns an observable sequence that stays connected to the source as long as
+ * there is at least one subscription to the observable sequence.
+ * 
+ * @param <T>
+ *            the value type
  */
 public final class OnSubscribeRefCount<T> implements OnSubscribe<T> {
-    final ConnectableObservable<? extends T> source;
-    final Object guard;
-    /** Guarded by guard. */
-    int index;
-    /** Guarded by guard. */
-    boolean emitting;
-    /** Guarded by guard. If true, indicates a connection request, false indicates a disconnect request. */
-    List<Token> queue;
-    /** Manipulated while in the serialized section. */
-    int count;
-    /** Manipulated while in the serialized section. */
-    Subscription connection;
-    /** Manipulated while in the serialized section. */
-    final Map<Token, Object> connectionStatus;
-    /** Occupied indicator. */
-    private static final Object OCCUPIED = new Object();
+
+    private final ConnectableObservable<? extends T> source;
+    private volatile CompositeSubscription baseSubscription = new CompositeSubscription();
+    private final AtomicInteger subscriptionCount = new AtomicInteger(0);
+
+    /**
+     * Use this lock for every subscription and disconnect action.
+     */
+    private final ReentrantLock lock = new ReentrantLock();
+
+    /**
+     * Constructor.
+     * 
+     * @param source
+     *            observable to apply ref count to
+     */
     public OnSubscribeRefCount(ConnectableObservable<? extends T> source) {
         this.source = source;
-        this.guard = new Object();
-        this.connectionStatus = new WeakHashMap<Token, Object>();
     }
 
     @Override
-    public void call(Subscriber<? super T> t1) {
-        int id;
-        synchronized (guard) {
-            id = ++index;
-        }
-        final Token t = new Token(id);
-        t1.add(Subscriptions.create(new Action0() {
-            @Override
-            public void call() {
-                disconnect(t);
-            }
-        }));
-        source.unsafeSubscribe(t1);
-        connect(t);
-    }
-    private void connect(Token id) {
-        List<Token> localQueue;
-        synchronized (guard) {
-            if (emitting) {
-                if (queue == null) {
-                    queue = new ArrayList<Token>();
-                }
-                queue.add(id);
-                return;
-            }
-            
-            localQueue = queue;
-            queue = null;
-            emitting = true;
-        }
-        boolean once = true;
-        do {
-            drain(localQueue);
-            if (once) {
-                once = false;
-                doConnect(id);
-            }
-            synchronized (guard) {
-                localQueue = queue;
-                queue = null;
-                if (localQueue == null) {
-                    emitting = false;
-                    return;
-                }
-            }
-        } while (true);
-    }
-    private void disconnect(Token id) {
-        List<Token> localQueue;
-        synchronized (guard) {
-            if (emitting) {
-                if (queue == null) {
-                    queue = new ArrayList<Token>();
-                }
-                queue.add(id.toDisconnect()); // negative value indicates disconnect
-                return;
-            }
-            
-            localQueue = queue;
-            queue = null;
-            emitting = true;
-        }
-        boolean once = true;
-        do {
-            drain(localQueue);
-            if (once) {
-                once = false;
-                doDisconnect(id);
-            }
-            synchronized (guard) {
-                localQueue = queue;
-                queue = null;
-                if (localQueue == null) {
-                    emitting = false;
-                    return;
+    public void call(final Subscriber<? super T> subscriber) {
+
+        lock.lock();
+        if (subscriptionCount.incrementAndGet() == 1) {
+
+            final AtomicBoolean writeLocked = new AtomicBoolean(true);
+
+            try {
+                // need to use this overload of connect to ensure that
+                // baseSubscription is set in the case that source is a
+                // synchronous Observable
+                source.connect(onSubscribe(subscriber, writeLocked));
+            } finally {
+                // need to cover the case where the source is subscribed to
+                // outside of this class thus preventing the above Action1
+                // being called
+                if (writeLocked.get()) {
+                    // Action1 was not called
+                    lock.unlock();
                 }
             }
-        } while (true);
-    }
-    private void drain(List<Token> localQueue) {
-        if (localQueue == null) {
-            return;
-        }
-        int n = localQueue.size();
-        for (int i = 0; i < n; i++) {
-            Token id = localQueue.get(i);
-            if (id.isDisconnect()) {
-                doDisconnect(id);
-            } else {
-                doConnect(id);
-            }
-        }
-    }
-    private void doConnect(Token id) {
-        // this method is called only once per id
-        // if add succeeds, id was not yet disconnected
-        if (connectionStatus.put(id, OCCUPIED) == null) {
-            if (count++ == 0) {
-                connection = source.connect();
-            }
         } else {
-            // connection exists due to disconnect, just remove
-            connectionStatus.remove(id);
-        }
-    }
-    private void doDisconnect(Token id) {
-        // this method is called only once per id
-        // if remove succeeds, id was connected
-        if (connectionStatus.remove(id) != null) {
-            if (--count == 0) {
-                connection.unsubscribe();
-                connection = null;
+            try {
+                // handle unsubscribing from the base subscription
+                subscriber.add(disconnect());
+
+                // ready to subscribe to source so do it
+                source.unsafeSubscribe(subscriber);
+            } finally {
+                // release the read lock
+                lock.unlock();
             }
-        } else {
-            // mark id as if connected
-            connectionStatus.put(id, OCCUPIED);
         }
+
     }
-    /** Token that represens a connection request or a disconnection request. */
-    private static final class Token {
-        final int id;
-        public Token(int id) {
-            this.id = id;
-        }
 
-        @Override
-        public boolean equals(Object obj) {
-            if (obj == null) {
-                return false;
-            }
-            if (obj.getClass() != getClass()) {
-                return false;
+    private Action1<Subscription> onSubscribe(final Subscriber<? super T> subscriber,
+            final AtomicBoolean writeLocked) {
+        return new Action1<Subscription>() {
+            @Override
+            public void call(Subscription subscription) {
+
+                try {
+                    baseSubscription.add(subscription);
+
+                    // handle unsubscribing from the base subscription
+                    subscriber.add(disconnect());
+
+                    // ready to subscribe to source so do it
+                    source.unsafeSubscribe(subscriber);
+                } finally {
+                    // release the write lock
+                    lock.unlock();
+                    writeLocked.set(false);
+                }
             }
-            int other = ((Token)obj).id;
-            return id == other || -id == other;
-        }
+        };
+    }
 
-        @Override
-        public int hashCode() {
-            return id < 0 ? -id : id;
-        }
-        public boolean isDisconnect() {
-            return id < 0;
-        }
-        public Token toDisconnect() {
-            if (id < 0) {
-                return this;
+    private Subscription disconnect() {
+        return Subscriptions.create(new Action0() {
+            @Override
+            public void call() {
+                lock.lock();
+                try {
+                    if (subscriptionCount.decrementAndGet() == 0) {
+                        baseSubscription.unsubscribe();
+                        // need a new baseSubscription because once
+                        // unsubscribed stays that way
+                        baseSubscription = new CompositeSubscription();
+                    }
+                } finally {
+                    lock.unlock();
+                }
             }
-            return new Token(-id);
-        }
+        });
     }
-}
+}

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

@@ -137,7 +137,13 @@ public void call() {
             }));
 
             // now that everything is hooked up let's subscribe
-            source.unsafeSubscribe(subscription);
+            // as long as the subscription is not null (which can happen if already unsubscribed)
+            boolean subscriptionIsNull;
+            synchronized(guard) {
+                subscriptionIsNull = subscription == null;
+            }
+            if (!subscriptionIsNull)
+                source.unsafeSubscribe(subscription);
         }
     }
-}
+}