Use AtomicReference

Author: ZacSweers

src/main/java/rx/schedulers/Schedulers.java

@@ -25,6 +25,7 @@
 import rx.plugins.RxJavaSchedulersHook;
 
 import java.util.concurrent.Executor;
+import java.util.concurrent.atomic.AtomicReference;
 
 /**
  * Static factory methods for creating Schedulers.
@@ -35,13 +36,21 @@ public final class Schedulers {
     private final Scheduler ioScheduler;
     private final Scheduler newThreadScheduler;
 
-    private static Schedulers INSTANCE;
+    private static final AtomicReference<Schedulers> INSTANCE = new AtomicReference<Schedulers>();
 
-    private static synchronized Schedulers getInstance() {
-        if (INSTANCE == null) {
-            INSTANCE = new Schedulers();
+    private static Schedulers getInstance() {
+        for (;;) {
+            Schedulers current = INSTANCE.get();
+            if (current != null) {
+                return current;
+            }
+            current = new Schedulers();
+            if (INSTANCE.compareAndSet(null, current)) {
+                return current;
+            } else {
+                shutdown();
+            }
         }
-        return INSTANCE;
     }
 
     private Schedulers() {
@@ -163,7 +172,7 @@ public static Scheduler from(Executor executor) {
     @Experimental
     public static void reset() {
         shutdown();
-        INSTANCE = null;
+        INSTANCE.set(null);
     }
 
     /**
@@ -205,11 +214,11 @@ public static void shutdown() {
             if (s.newThreadScheduler instanceof SchedulerLifecycle) {
                 ((SchedulerLifecycle) s.newThreadScheduler).shutdown();
             }
-            
+
             GenericScheduledExecutorService.INSTANCE.shutdown();
-            
+
             RxRingBuffer.SPSC_POOL.shutdown();
-            
+
             RxRingBuffer.SPMC_POOL.shutdown();
         }
     }