6323 resource creation deadlock (#6324)

* make map reads concurrent

* change log

hapi-fhir-base/src/main/java/ca/uhn/fhir/context/BaseRuntimeElementDefinition.java

@@ -33,14 +33,15 @@
 import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
+import java.util.concurrent.ConcurrentHashMap;
 
 public abstract class BaseRuntimeElementDefinition<T extends IBase> {
 
 	private static final Class<Void> VOID_CLASS = Void.class;
 	private final Class<? extends T> myImplementingClass;
 	private final String myName;
 	private final boolean myStandardType;
-	private Map<Class<?>, Constructor<T>> myConstructors = Collections.synchronizedMap(new HashMap<>());
+	private final Map<Class<?>, Constructor<T>> myConstructors = new ConcurrentHashMap<>();
 	private List<RuntimeChildDeclaredExtensionDefinition> myExtensions = new ArrayList<>();
 	private List<RuntimeChildDeclaredExtensionDefinition> myExtensionsModifier = new ArrayList<>();
 	private List<RuntimeChildDeclaredExtensionDefinition> myExtensionsNonModifier = new ArrayList<>();
@@ -84,27 +85,24 @@ private Constructor<T> getConstructor(@Nullable Object theArgument) {
 			argumentType = theArgument.getClass();
 		}
 
-		Constructor<T> retVal = myConstructors.get(argumentType);
-		if (retVal == null) {
+		Constructor<T> retVal = myConstructors.computeIfAbsent(argumentType, type -> {
 			for (Constructor<?> next : getImplementingClass().getConstructors()) {
-				if (argumentType == VOID_CLASS) {
+				if (type == VOID_CLASS) {
 					if (next.getParameterTypes().length == 0) {
-						retVal = (Constructor<T>) next;
-						break;
-					}
-				} else if (next.getParameterTypes().length == 1) {
-					if (next.getParameterTypes()[0].isAssignableFrom(argumentType)) {
-						retVal = (Constructor<T>) next;
-						break;
+						return (Constructor<T>) next;
 					}
+				} else if (next.getParameterTypes().length == 1 && next.getParameterTypes()[0].isAssignableFrom(type)) {
+					return (Constructor<T>) next;
 				}
 			}
-			if (retVal == null) {
-				throw new ConfigurationException(Msg.code(1695) + "Class " + getImplementingClass()
-						+ " has no constructor with a single argument of type " + argumentType);
-			}
-			myConstructors.put(argumentType, retVal);
+			return null;
+		});
+
+		if (retVal == null) {
+			throw new ConfigurationException(Msg.code(1695) + "Class " + getImplementingClass()
+					+ " has no constructor with a single argument of type " + argumentType);
 		}
+
 		return retVal;
 	}
 

hapi-fhir-docs/src/main/resources/ca/uhn/hapi/fhir/changelog/7_6_0/6323-concurrent-constructor-access.yaml

@@ -0,0 +1,5 @@
+---
+type: perf
+issue: 6323
+title: "A synchronization choke point was removed from the model object initialization code, reducing the risk of
+multi-thread contention."