errors: cache source if loaded from disk

Refs: #41541

Author: bcoe

lib/internal/source_map/prepare_stack_trace.js

@@ -1,6 +1,7 @@
 'use strict';
 
 const {
+  SafeMap,
   ArrayPrototypeIndexOf,
   ArrayPrototypeJoin,
   ArrayPrototypeMap,
@@ -170,6 +171,8 @@ function getErrorSource(
   return exceptionLine;
 }
 
+// Only load source from disk once:
+const sourcesCache = new SafeMap();
 function getOriginalSource(payload, originalSourcePath) {
   let source;
   const originalSourcePathNoScheme =
@@ -181,11 +184,14 @@ function getOriginalSource(payload, originalSourcePath) {
     // First we check if the original source content was provided in the
     // source map itself:
     source = payload.sourcesContent[sourceContentIndex];
+  } else if (sourcesCache.has(originalSourcePathNoScheme)) {
+    return sourcesCache.get(originalSourcePathNoScheme);
   } else {
     // If no sourcesContent was found, attempt to load the original source
     // from disk:
     try {
       source = readFileSync(originalSourcePathNoScheme, 'utf8');
+      sourcesCache.set(originalSourcePathNoScheme, source);
     } catch (err) {
       debug(err);
       source = '';