Merge pull request #2990 from davidmoten/subscriber-readability

Improve Subscriber readability

Author: benjchristensen

src/main/java/rx/Subscriber.java

@@ -31,20 +31,23 @@
  *          the type of items the Subscriber expects to observe
  */
 public abstract class Subscriber<T> implements Observer<T>, Subscription {
+    
+    // represents requested not set yet
+    private static final Long NOT_SET = Long.MIN_VALUE;
 
-    private final SubscriptionList cs;
-    private final Subscriber<?> op;
+    private final SubscriptionList subscriptions;
+    private final Subscriber<?> subscriber;
     /* protected by `this` */
-    private Producer p;
+    private Producer producer;
     /* protected by `this` */
-    private long requested = Long.MIN_VALUE; // default to not set
+    private long requested = NOT_SET; // default to not set
 
     protected Subscriber() {
         this(null, false);
     }
 
-    protected Subscriber(Subscriber<?> op) {
-        this(op, true);
+    protected Subscriber(Subscriber<?> subscriber) {
+        this(subscriber, true);
     }
 
     /**
@@ -53,15 +56,15 @@ protected Subscriber(Subscriber<?> op) {
      * <p>
      * To retain the chaining of subscribers, add the created instance to {@code op} via {@link #add}.
      * 
-     * @param op
+     * @param subscriber
      *            the other Subscriber
      * @param shareSubscriptions
      *            {@code true} to share the subscription list in {@code op} with this instance
      * @since 1.0.6
      */
-    protected Subscriber(Subscriber<?> op, boolean shareSubscriptions) {
-        this.op = op;
-        this.cs = shareSubscriptions && op != null ? op.cs : new SubscriptionList();
+    protected Subscriber(Subscriber<?> subscriber, boolean shareSubscriptions) {
+        this.subscriber = subscriber;
+        this.subscriptions = shareSubscriptions && subscriber != null ? subscriber.subscriptions : new SubscriptionList();
     }
 
     /**
@@ -73,12 +76,12 @@ protected Subscriber(Subscriber<?> op, boolean shareSubscriptions) {
      *            the {@code Subscription} to add
      */
     public final void add(Subscription s) {
-        cs.add(s);
+        subscriptions.add(s);
     }
 
     @Override
     public final void unsubscribe() {
-        cs.unsubscribe();
+        subscriptions.unsubscribe();
     }
 
     /**
@@ -88,7 +91,7 @@ public final void unsubscribe() {
      */
     @Override
     public final boolean isUnsubscribed() {
-        return cs.isUnsubscribed();
+        return subscriptions.isUnsubscribed();
     }
 
     /**
@@ -124,57 +127,64 @@ protected final void request(long n) {
         if (n < 0) {
             throw new IllegalArgumentException("number requested cannot be negative: " + n);
         } 
-        Producer shouldRequest = null;
+        
+        // if producer is set then we will request from it
+        // otherwise we increase the requested count by n
+        Producer producerToRequestFrom = null;
         synchronized (this) {
-            if (p != null) {
-                shouldRequest = p;
-            } else if (requested == Long.MIN_VALUE) {
-                requested = n;
-            } else { 
-                final long total = requested + n;
-                // check if overflow occurred
-                if (total < 0) {
-                    requested = Long.MAX_VALUE;
-                } else {
-                    requested = total;
-                }
+            if (producer != null) {
+                producerToRequestFrom = producer;
+            } else {
+                addToRequested(n);
+                return;
             }
         }
-        // after releasing lock
-        if (shouldRequest != null) {
-            shouldRequest.request(n);
-        }
+        // after releasing lock (we should not make requests holding a lock)
+        producerToRequestFrom.request(n);
     }
 
+    private void addToRequested(long n) {
+        if (requested == NOT_SET) {
+            requested = n;
+        } else { 
+            final long total = requested + n;
+            // check if overflow occurred
+            if (total < 0) {
+                requested = Long.MAX_VALUE;
+            } else {
+                requested = total;
+            }
+        }
+    }
+    
     /**
      * @warn javadoc description missing
      * @warn param producer not described
-     * @param producer
+     * @param p
      */
-    public void setProducer(Producer producer) {
+    public void setProducer(Producer p) {
         long toRequest;
-        boolean setProducer = false;
+        boolean passToSubscriber = false;
         synchronized (this) {
             toRequest = requested;
-            p = producer;
-            if (op != null) {
+            producer = p;
+            if (subscriber != null) {
                 // middle operator ... we pass thru unless a request has been made
-                if (toRequest == Long.MIN_VALUE) {
+                if (toRequest == NOT_SET) {
                     // we pass-thru to the next producer as nothing has been requested
-                    setProducer = true;
+                    passToSubscriber = true;
                 }
-
             }
         }
         // do after releasing lock
-        if (setProducer) {
-            op.setProducer(p);
+        if (passToSubscriber) {
+            subscriber.setProducer(producer);
         } else {
             // we execute the request with whatever has been requested (or Long.MAX_VALUE)
-            if (toRequest == Long.MIN_VALUE) {
-                p.request(Long.MAX_VALUE);
+            if (toRequest == NOT_SET) {
+                producer.request(Long.MAX_VALUE);
             } else {
-                p.request(toRequest);
+                producer.request(toRequest);
             }
         }
     }