Merge pull request #1276 from mattrjacobs/lazy-observable-collapser-t…

…o-observable

Moved all work performed in HystrixObservableCommand.toObservable inside an Observable.defer to make it lazy

hystrix-core/src/main/java/com/netflix/hystrix/HystrixObservableCollapser.java

@@ -34,6 +34,7 @@
 import rx.Subscription;
 import rx.functions.Action0;
 import rx.functions.Action1;
+import rx.functions.Func0;
 import rx.functions.Func1;
 import rx.schedulers.Schedulers;
 import rx.subjects.ReplaySubject;
@@ -439,39 +440,44 @@ public Observable<ResponseType> toObservable() {
      */
     public Observable<ResponseType> toObservable(Scheduler observeOn) {
 
-        final boolean isRequestCacheEnabled = getProperties().requestCacheEnabled().get();
-
-        /* try from cache first */
-        if (isRequestCacheEnabled) {
-            HystrixCachedObservable<ResponseType> fromCache = requestCache.get(getCacheKey());
-            if (fromCache != null) {
-                metrics.markResponseFromCache();
-                return fromCache.toObservable();
-            }
-        }
+        return Observable.defer(new Func0<Observable<ResponseType>>() {
+            @Override
+            public Observable<ResponseType> call() {
+                final boolean isRequestCacheEnabled = getProperties().requestCacheEnabled().get();
+
+                /* try from cache first */
+                if (isRequestCacheEnabled) {
+                    HystrixCachedObservable<ResponseType> fromCache = requestCache.get(getCacheKey());
+                    if (fromCache != null) {
+                        metrics.markResponseFromCache();
+                        return fromCache.toObservable();
+                    }
+                }
 
-        RequestCollapser<BatchReturnType, ResponseType, RequestArgumentType> requestCollapser = collapserFactory.getRequestCollapser(collapserInstanceWrapper);
-        Observable<ResponseType> response = requestCollapser.submitRequest(getRequestArgument());
-        metrics.markRequestBatched();
-        if (isRequestCacheEnabled) {
-            /*
-             * A race can occur here with multiple threads queuing but only one will be cached.
-             * This means we can have some duplication of requests in a thread-race but we're okay
-             * with having some inefficiency in duplicate requests in the same batch
-             * and then subsequent requests will retrieve a previously cached Observable.
-             * 
-             * If this is an issue we can make a lazy-future that gets set in the cache
-             * then only the winning 'put' will be invoked to actually call 'submitRequest'
-             */
-            HystrixCachedObservable<ResponseType> toCache = HystrixCachedObservable.from(response);
-            HystrixCachedObservable<ResponseType> fromCache = requestCache.putIfAbsent(getCacheKey(), toCache);
-            if (fromCache == null) {
-                return toCache.toObservable();
-            } else {
-                return fromCache.toObservable();
+                RequestCollapser<BatchReturnType, ResponseType, RequestArgumentType> requestCollapser = collapserFactory.getRequestCollapser(collapserInstanceWrapper);
+                Observable<ResponseType> response = requestCollapser.submitRequest(getRequestArgument());
+                metrics.markRequestBatched();
+                if (isRequestCacheEnabled) {
+                    /*
+                     * A race can occur here with multiple threads queuing but only one will be cached.
+                     * This means we can have some duplication of requests in a thread-race but we're okay
+                     * with having some inefficiency in duplicate requests in the same batch
+                     * and then subsequent requests will retrieve a previously cached Observable.
+                     *
+                     * If this is an issue we can make a lazy-future that gets set in the cache
+                     * then only the winning 'put' will be invoked to actually call 'submitRequest'
+                     */
+                    HystrixCachedObservable<ResponseType> toCache = HystrixCachedObservable.from(response);
+                    HystrixCachedObservable<ResponseType> fromCache = requestCache.putIfAbsent(getCacheKey(), toCache);
+                    if (fromCache == null) {
+                        return toCache.toObservable();
+                    } else {
+                        return fromCache.toObservable();
+                    }
+                }
+                return response;
             }
-        }
-        return response;
+        });
     }
 
     /**