Clean up use of EmptyContext.INSTANCE

Author: mcculls

components/context/src/main/java/datadog/context/EmptyContextContinuation.java

@@ -0,0 +1,30 @@
+package datadog.context;
+
+/** {@link ContextContinuation} that has no effect on execution units. */
+final class NoopContextContinuation implements ContextContinuation {
+  static final ContextContinuation ROOT_CONTINUATION = new NoopContextContinuation(Context.root());
+
+  private final Context context;
+
+  private NoopContextContinuation(Context context) {
+    this.context = context;
+  }
+
+  @Override
+  public ContextContinuation hold() {
+    return this;
+  }
+
+  @Override
+  public Context context() {
+    return context;
+  }
+
+  @Override
+  public ContextScope resume() {
+    return NoopContextScope.create(context);
+  }
+
+  @Override
+  public void release() {}
+}

components/context/src/main/java/datadog/context/NoopContextContinuation.java

@@ -4,7 +4,7 @@
 
 /** {@link ContextScope} that has no effect on execution units. */
 final class NoopContextScope extends WeakReference<Context> implements ContextScope {
-  private static final ContextScope ROOT_SCOPE = new NoopContextScope(Context.root());
+  static final ContextScope ROOT_SCOPE = new NoopContextScope(Context.root());
 
   private static final int CACHE_SIZE = 32; // must be power of 2
   private static final int SLOT_MASK = CACHE_SIZE - 1;

components/context/src/main/java/datadog/context/NoopContextScope.java

@@ -9,7 +9,7 @@ final class ThreadLocalContextManager implements ContextManager {
   static final ThreadLocalContextManager INSTANCE = new ThreadLocalContextManager();
 
   private static final ThreadLocal<Context[]> CURRENT_HOLDER =
-      ThreadLocal.withInitial(() -> new Context[] {EmptyContext.INSTANCE});
+      ThreadLocal.withInitial(() -> new Context[] {Context.root()});
 
   private final Object listenersWriteLock = new Object();
   private volatile ContextListener[] listeners = {};
@@ -68,7 +68,7 @@ public Context swap(Context context) {
   @Override
   public ContextContinuation capture(Context context) {
     if (context == Context.root()) {
-      return EmptyContextContinuation.INSTANCE;
+      return NoopContextContinuation.ROOT_CONTINUATION;
     } else {
       return new ContextContinuationImpl(context);
     }

components/context/src/main/java/datadog/context/ThreadLocalContextManager.java

@@ -73,17 +73,7 @@ public Context current() {
 
           @Override
           public ContextScope attach(Context context) {
-            return new ContextScope() {
-              @Override
-              public Context context() {
-                return root();
-              }
-
-              @Override
-              public void close() {
-                // no-op
-              }
-            };
+            return NoopContextScope.ROOT_SCOPE;
           }
 
           @Override
@@ -93,7 +83,7 @@ public Context swap(Context context) {
 
           @Override
           public ContextContinuation capture(Context context) {
-            return EmptyContextContinuation.INSTANCE;
+            return NoopContextContinuation.ROOT_CONTINUATION;
           }
 
           @Override