Switch to mutex

freva/src/drs/metadata.rs

@@ -4,7 +4,7 @@ mod config_builder;
 pub mod custom;
 
 use core::fmt;
-use std::sync::RwLock;
+use std::sync::Mutex;
 use std::{
     collections::HashMap,
     fmt::Formatter,
@@ -21,7 +21,7 @@ use drs::{
 use lazy_static::lazy_static;
 use netcdf::AttrValue;
 use thiserror::Error;
-use tracing::{debug, error};
+use tracing::{debug, error, trace};
 
 pub use config_builder::ConfigBuilder;
 use custom::Custom;
@@ -395,26 +395,29 @@ lazy_static! {
     /// This is done as a global cache right now just because performance shouldn't be a large concern as we expect far
     /// more reads than writes and this implementation is simpler than e.g. having the [`drs`] crate load and hold the
     /// mapping values ahead of time.
-    static ref CMIP6_ATTR_CACHE: RwLock<HashMap<String, (String, String)>> =
-        RwLock::new(HashMap::new());
+    static ref CMIP6_ATTR_CACHE: Mutex<HashMap<String, (String, String)>> =
+        Mutex::new(HashMap::new());
 }
 
 /// Transforms a [`Cmip6`] object into [`Metadata`]. This is handled differently from the others because CMIP6's path
 /// does not contain all the data [`Metadata`] needs. To get the rest we need to either use mapping tables maintained
 /// separately from the DRS spec or, as we do here, open the files up and pull the data from their attributes.
 fn metadata_from_cmip6(cmip: Cmip6, root_dir: &Utf8Path) -> Result<Metadata, ExtractMetadataError> {
-    let (frequency, realm) =
-        if let Some((freq, realm)) = CMIP6_ATTR_CACHE.read().unwrap().get(cmip.metadata.table_id) {
+    let (frequency, realm) = {
+        let mut guard = CMIP6_ATTR_CACHE.lock().unwrap();
+        if let Some((freq, realm)) = guard.get(cmip.metadata.table_id) {
             (freq.clone(), realm.clone())
         } else {
+            trace!("attributes not cached, opening file to extract");
             let (frequency, realm) = get_cmip6_attrs(&root_dir.join(cmip.path))?;
 
-            CMIP6_ATTR_CACHE.write().unwrap().insert(
+            guard.insert(
                 cmip.metadata.table_id.to_owned(),
                 (frequency.clone(), realm.clone()),
             );
             (frequency, realm)
-        };
+        }
+    };
 
     let m = &cmip.metadata;
     Ok(Metadata {