Attempt to fix reference counting issues in ES client instrumentation

CHANGELOG.asciidoc

@@ -40,6 +40,7 @@ Use subheadings with the "=====" level for adding notes for unreleased changes:
 [float]
 ===== Bug fixes
 * Fixed SQS NoClassDefFoundError in AWS SDK instrumentation - {pull}3254[#3254]
+* Fixed reference counting issues in elasticsearch instrumentation - {pull}3256[#3256]
 
 [[release-notes-1.x]]
 === Java Agent version 1.x

apm-agent-plugins/apm-es-restclient-plugin/apm-es-restclient-plugin-common/src/main/java/co/elastic/apm/agent/esrestclient/ResponseListenerWrapper.java

@@ -53,15 +53,15 @@ ResponseListenerWrapper withClientSpan(ResponseListener delegate, Span<?> span)
         // Order is important due to visibility - write to span last on this (initiating) thread
         this.delegate = delegate;
         this.isClientSpan = true;
-        this.context = span;
+        setContext(span);
         return this;
     }
 
     ResponseListenerWrapper withContextPropagation(ResponseListener delegate, AbstractSpan<?> context) {
         // Order is important due to visibility - write to span last on this (initiating) thread
         this.delegate = delegate;
         this.isClientSpan = false;
-        this.context = context;
+        setContext(context);
         return this;
     }
 
@@ -149,10 +149,20 @@ private void finishClientSpan(@Nullable Response response, @Nullable Throwable t
         }
     }
 
+    private void setContext(@Nullable AbstractSpan<?> newContext) {
+        if (newContext != null) {
+            newContext.incrementReferences();
+        }
+        if (context != null) {
+            context.decrementReferences();
+        }
+        context = newContext;
+    }
+
     @Override
     public void resetState() {
         delegate = null;
-        context = null;
+        setContext(null);
         isClientSpan = false;
     }
 }