feat(context): Introduce compositor extractor carrier cache

components/context/src/main/java/datadog/context/propagation/CompositePropagator.java

@@ -1,6 +1,9 @@
 package datadog.context.propagation;
 
 import datadog.context.Context;
+import java.util.ArrayList;
+import java.util.List;
+import java.util.function.BiConsumer;
 
 class CompositePropagator implements Propagator {
   private final Propagator[] propagators;
@@ -18,9 +21,35 @@ public <C> void inject(Context context, C carrier, CarrierSetter<C> setter) {
 
   @Override
   public <C> Context extract(Context context, C carrier, CarrierVisitor<C> visitor) {
+    // Extract and cache carrier key/value pairs
+    CarrierCache carrierCache = new CarrierCache();
+    visitor.forEachKeyValue(carrier, carrierCache);
+    // Run the multiple extractions on cache
     for (Propagator propagator : this.propagators) {
-      context = propagator.extract(context, carrier, visitor);
+      context = propagator.extract(context, carrierCache, carrierCache);
     }
     return context;
   }
+
+  static class CarrierCache implements BiConsumer<String, String>, CarrierVisitor<CarrierCache> {
+    /** Cached key/values from carrier (even indexes are keys, odd indexes are values). */
+    private final List<String> keysAndValues;
+
+    public CarrierCache() {
+      this.keysAndValues = new ArrayList<>(32);
+    }
+
+    @Override
+    public void accept(String key, String value) {
+      this.keysAndValues.add(key);
+      this.keysAndValues.add(value);
+    }
+
+    @Override
+    public void forEachKeyValue(CarrierCache carrier, BiConsumer<String, String> visitor) {
+      for (int i = 0; i < carrier.keysAndValues.size() - 1; i += 2) {
+        visitor.accept(carrier.keysAndValues.get(i), carrier.keysAndValues.get(i + 1));
+      }
+    }
+  }
 }