Refactoring: move creation of instance_fields_hierarchy to JavaClass

vm/src/heap/java_instance.rs

@@ -81,7 +81,7 @@ pub(crate) enum HeapValue {
     Arr(Array),
 }
 
-impl<'a> JavaInstance {
+impl JavaInstance {
     pub fn new(
         instance_name: String,
         fields: IndexMap<ClassName, IndexMap<FieldNameType, Field>>,

vm/src/method_area/java_class.rs

@@ -1,10 +1,12 @@
 use crate::execution_engine::executor::Executor;
-use crate::heap::java_instance::FieldNameType;
+use crate::heap::java_instance::{ClassName, FieldNameType};
 use crate::method_area::cpool_helper::CPoolHelper;
 use crate::method_area::field::Field;
 use crate::method_area::java_method::JavaMethod;
+use crate::method_area::method_area::with_method_area;
 use indexmap::IndexMap;
 use jdescriptor::TypeDescriptor;
+use once_cell::sync::OnceCell;
 use std::collections::{HashMap, HashSet};
 use std::sync::atomic::{AtomicBool, Ordering};
 use std::sync::Arc;
@@ -23,6 +25,8 @@ pub(crate) struct JavaClass {
     access_flags: u16,
 
     static_fields_initialized: AtomicBool,
+
+    instance_fields_hierarchy: OnceCell<IndexMap<ClassName, IndexMap<FieldNameType, Field>>>,
 }
 
 #[derive(Debug)]
@@ -73,6 +77,7 @@ impl JavaClass {
             interfaces,
             access_flags,
             static_fields_initialized: AtomicBool::new(false),
+            instance_fields_hierarchy: OnceCell::new(),
         }
     }
 
@@ -194,6 +199,22 @@ impl JavaClass {
             ))
         })
     }
+
+    pub fn instance_fields_hierarchy(
+        &self,
+    ) -> crate::error::Result<&IndexMap<ClassName, IndexMap<FieldNameType, Field>>> {
+        Ok(&self.instance_fields_hierarchy.get_or_init(|| {
+            let mut instance_fields_hierarchy = IndexMap::new();
+            with_method_area(|area| {
+                area.lookup_and_fill_instance_fields_hierarchy(
+                    &self.this_class_name,
+                    &mut instance_fields_hierarchy,
+                )
+            }).expect("error getting instance fields hierarchy");
+
+            instance_fields_hierarchy
+        }))
+    }
 }
 
 impl Methods {

vm/src/method_area/method_area.rs

@@ -374,19 +374,14 @@ impl MethodArea {
         &self,
         class_name: &str,
     ) -> crate::error::Result<JavaInstance> {
-        let mut instance_fields_hierarchy = IndexMap::new();
-        self.lookup_and_fill_instance_fields_hierarchy(
-            class_name,
-            &mut instance_fields_hierarchy,
-        )?;
-
+        let jc = with_method_area(|area| area.get(class_name))?;
         Ok(JavaInstance::new(
             class_name.to_string(),
-            instance_fields_hierarchy,
+            jc.instance_fields_hierarchy()?.clone(),
         ))
     }
 
-    fn lookup_and_fill_instance_fields_hierarchy(
+    pub(crate) fn lookup_and_fill_instance_fields_hierarchy(
         &self,
         class_name: &str,
         instance_fields_hierarchy: &mut IndexMap<ClassName, IndexMap<FieldNameType, Field>>,