fix ring context

Author: qiweiii

Utils/Sources/bandersnatch/src/bandersnatch_vrfs.rs

@@ -25,16 +25,23 @@ pub struct RingVrfSignature {
 }
 
 pub fn ring_context(size: usize) -> Option<RingProofParams> {
+    use std::collections::HashMap;
     use std::sync::OnceLock;
-    static RING_CONTEXT: OnceLock<Option<RingProofParams>> = OnceLock::new();
-
-    // size is number of validators, so it won't change
-    RING_CONTEXT
-        .get_or_init(|| {
-            let pcs_params = ring_context_params();
-            RingProofParams::from_pcs_params(size, pcs_params.clone()).ok()
-        })
-        .clone()
+
+    static RING_CONTEXTS: OnceLock<std::sync::Mutex<HashMap<usize, Option<RingProofParams>>>> =
+        OnceLock::new();
+
+    let contexts = RING_CONTEXTS.get_or_init(|| std::sync::Mutex::new(HashMap::new()));
+    let mut cache = contexts.lock().unwrap();
+
+    if let Some(cached_params) = cache.get(&size) {
+        cached_params.clone()
+    } else {
+        let pcs_params = ring_context_params();
+        let params = RingProofParams::from_pcs_params(size, pcs_params.clone()).ok();
+        cache.insert(size, params.clone());
+        params
+    }
 }
 
 fn ring_context_params() -> &'static PcsParams {