Add a global class cache to VM

vm/rust/Cargo.toml

@@ -15,6 +15,8 @@ cairo-lang-casm = "2.1.0"
 cairo-lang-starknet = "2.1.0"
 indexmap = "1.9.2"
 starknet = { rev = "starknet-core/v0.4.0", git = "https://github.com/xJonathanLEI/starknet-rs" }
+cached = "0.44.0"
+once_cell = "1.18.0"
 
 [lib]
 crate-type = ["staticlib"]

vm/rust/src/juno_state_reader.rs

@@ -1,6 +1,6 @@
 use std::{
     ffi::{c_char, c_uchar, c_void, CStr},
-    slice,
+    slice, sync::Mutex,
 };
 
 use blockifier::{
@@ -10,9 +10,10 @@ use blockifier::{
 use starknet_api::core::{ClassHash, CompiledClassHash, ContractAddress, Nonce};
 use starknet_api::hash::StarkFelt;
 use starknet_api::state::StorageKey;
-
+use cached::{SizedCache, Cached};
 use blockifier::execution::contract_class::ContractClass;
 use blockifier::state::errors::StateError;
+use once_cell::sync::Lazy;
 
 extern "C" {
     fn JunoFree(ptr: *const c_void);
@@ -34,6 +35,11 @@ extern "C" {
         -> *const c_char;
 }
 
+static CLASS_CACHE: Lazy<Mutex<SizedCache<ClassHash, ContractClass>>> = Lazy::new(|| {
+    Mutex::new(SizedCache::with_size(128))
+});
+
+
 pub struct JunoStateReader {
     pub handle: usize, // uintptr_t equivalent
 }
@@ -108,13 +114,21 @@ impl StateReader for JunoStateReader {
         &mut self,
         class_hash: &ClassHash,
     ) -> StateResult<ContractClass> {
+        if let Some(cached_class) = CLASS_CACHE.lock().unwrap().cache_get(class_hash) {
+            return Ok(cached_class.clone())
+        }
+
         let class_hash_bytes = felt_to_byte_array(&class_hash.0);
         let ptr = unsafe { JunoStateGetCompiledClass(self.handle, class_hash_bytes.as_ptr()) };
         if ptr.is_null() {
             Err(StateError::UndeclaredClassHash(*class_hash))
         } else {
             let json_str = unsafe { CStr::from_ptr(ptr) }.to_str().unwrap();
             let contract_class = contract_class_from_json_str(json_str);
+            if let Ok(class) = &contract_class {
+                CLASS_CACHE.lock().unwrap().cache_set(*class_hash, class.clone());
+            }
+
             unsafe { JunoFree(ptr as *const c_void) };
 
             contract_class.map_err(|_| {