Merge pull request Netflix#1419 from mattrjacobs/never-let-maximum-si…

…ze-and-core-size-diverge-unless-user-opts-in

When user has not opted in to letting core/maximum threadpools diverge, ensure dynamic updates to coreSize apply to both

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

@@ -221,10 +221,16 @@ private void touchConfig() {
             boolean maxTooLow = false;
 
             if (allowSizesToDiverge && dynamicMaximumSize < dynamicCoreSize) {
+                //if user sets maximum < core (or defaults get us there), we need to maintain invariant of core <= maximum
                 dynamicMaximumSize = dynamicCoreSize;
                 maxTooLow = true;
             }
 
+            if (!allowSizesToDiverge) {
+                //if user has not opted in to allowing sizes to diverge, ensure maximum == core
+                dynamicMaximumSize = dynamicCoreSize;
+            }
+
             // In JDK 6, setCorePoolSize and setMaximumPoolSize will execute a lock operation. Avoid them if the pool size is not changed.
             if (threadPool.getCorePoolSize() != dynamicCoreSize || (allowSizesToDiverge && threadPool.getMaximumPoolSize() != dynamicMaximumSize)) {
                 if (maxTooLow) {