Backport some performance work for tracing

Author: andrebrait

main/api/src/main/java/org/elasticsoftware/elasticactors/tracing/TraceContext.java

@@ -26,31 +26,69 @@ public TraceContext(
         @Nonnull String traceId,
         @Nullable String parentId,
         @Nullable Map<String, String> baggage)
+    {
+        this(spanId, traceId, parentId, baggage, false);
+    }
+
+    /**
+     * Constructor that allows the user to inform if the provided baggage map is immutable,
+     * preventing unnecessary copies if so.
+     *
+     * This is provided for optimization purposes.
+     * Passing a map that is not mutable here and changing it afterwards may
+     * (and very likely will) corrupt the thread's MDC.
+     */
+    public TraceContext(
+        @Nonnull String spanId,
+        @Nonnull String traceId,
+        @Nullable String parentId,
+        @Nullable Map<String, String> baggage,
+        boolean immutableBaggageMap)
     {
         this.spanId = Objects.requireNonNull(spanId);
         this.traceId = Objects.requireNonNull(traceId);
         this.parentId = parentId;
-        this.baggage = baggage;
+        this.baggage = !immutableBaggageMap && baggage != null
+            ? Collections.unmodifiableMap(new HashMap<>(baggage))
+            : baggage;
     }
 
     public TraceContext(@Nullable TraceContext parent) {
-        this(parent, parent == null ? null : parent.baggage);
+        this(parent, parent == null ? null : parent.baggage, true);
     }
 
     public TraceContext(@Nullable Map<String, String> baggage) {
-        this(null, baggage);
+        this(null, baggage, false);
+    }
+
+    public TraceContext(@Nullable TraceContext parent, @Nullable Map<String, String> baggage) {
+        this(parent, baggage, false);
     }
 
-    private TraceContext(@Nullable TraceContext parent, @Nullable Map<String, String> baggage) {
+    /**
+     * Constructor that allows the user to inform if the provided baggage map is immutable,
+     * preventing unnecessary copies if so.
+     *
+     * This is provided for optimization purposes.
+     * Passing a map that is not mutable here and changing it afterwards may
+     * (and very likely will) corrupt the thread's MDC.
+     */
+    public TraceContext(
+        @Nullable TraceContext parent,
+        @Nullable Map<String, String> baggage,
+        boolean immutableBaggageMap)
+    {
         Random prng = ThreadLocalRandom.current();
         this.spanId = toHexString(prng.nextLong());
         this.traceId = parent == null || parent.getTraceId().isEmpty()
-                ? nextTraceIdHigh(prng) + this.spanId
-                : parent.getTraceId();
+            ? nextTraceIdHigh(prng) + this.spanId
+            : parent.getTraceId();
         this.parentId = parent == null || parent.getSpanId().isEmpty()
-                ? null
-                : parent.getSpanId();
-        this.baggage = baggage == null ? null : Collections.unmodifiableMap(new HashMap<>(baggage));
+            ? null
+            : parent.getSpanId();
+        this.baggage = !immutableBaggageMap && baggage != null
+            ? Collections.unmodifiableMap(new HashMap<>(baggage))
+            : baggage;
     }
 
     /**

main/messaging/src/main/java/org/elasticsoftware/elasticactors/serialization/internal/tracing/TraceContextDeserializer.java

@@ -18,7 +18,8 @@ public static TraceContext deserialize(Messaging.TraceContext traceContext) {
             traceContext.hasSpanId() ? traceContext.getSpanId() : "",
             traceContext.hasTraceId() ? traceContext.getTraceId() : "",
             traceContext.hasParentId() ? traceContext.getParentId() : null,
-            baggage != null && !baggage.isEmpty() ? baggage : null
+            baggage.isEmpty() ? null : baggage,
+            true
         );
         return deserialized.isEmpty() ? null : deserialized;
     }

main/tracing/src/main/java/org/elasticsoftware/elasticactors/tracing/service/TracingMessagingContextManager.java

@@ -326,31 +326,32 @@ private static void updateBaggage(TraceContext current, TraceContext next) {
         try {
             Map<String, String> oldBaggage = current != null ? current.getBaggage() : null;
             Map<String, String> nextBaggage = next != null ? next.getBaggage() : null;
-            if (oldBaggage != null) {
-                for (Map.Entry<String, String> oldEntry : oldBaggage.entrySet()) {
-                    String key = oldEntry.getKey();
-                    String value = oldEntry.getValue();
-                    String nextValue = nextBaggage != null ? nextBaggage.get(key) : null;
+            if (oldBaggage == nextBaggage) {
+                return;
+            }
+            if (oldBaggage == null) {
+                nextBaggage.forEach(TracingMessagingContextManager::putOnMDC);
+            } else if (nextBaggage == null) {
+                oldBaggage.keySet().forEach(key -> putOnMDC(key, null));
+            } else {
+                oldBaggage.forEach((key, value) -> {
+                    String nextValue = nextBaggage.get(key);
                     // Will set the new value if present, and remove it if absent
                     if (!Objects.equals(value, nextValue)) {
                         putOnMDC(key, nextValue);
                     }
-                }
-            }
-            if (nextBaggage != null) {
-                for (Map.Entry<String, String> nextEntry : nextBaggage.entrySet()) {
-                    String key = nextEntry.getKey();
-                    String value = nextEntry.getValue();
-                    String oldValue = oldBaggage != null ? oldBaggage.get(key) : null;
+                });
+                nextBaggage.forEach((key, value) -> {
+                    String oldValue = oldBaggage.get(key);
                     // Would have been processed when processing oldBaggage
                     if (oldValue != null) {
-                        continue;
+                        return;
                     }
                     // Only insert if the old value was null and the new one isn't
                     if (value != null) {
                         putOnMDC(key, value);
                     }
-                }
+                });
             }
         } catch (Exception e) {
             logger.error(