SERVER-46494 improve perf of '$function'

2 files changed, 8 insertions, 1 deletions

diff --git a/src/mongo/scripting/mozjs/implscope.cpp b/src/mongo/scripting/mozjs/implscope.cpp
index f06a20bfc0a..32883343ab0 100644
--- a/src/mongo/scripting/mozjs/implscope.cpp
+++ b/src/mongo/scripting/mozjs/implscope.cpp
@@ -630,9 +630,14 @@ bool hasFunctionIdentifier(StringData code) {
 ScriptingFunction MozJSImplScope::_createFunction(const char* raw) {
     return _runSafely([&] {
         JS::RootedValue fun(_context);
+        auto it = _funcCodeToHandleMap.find(StringData(raw));
+        if (it != _funcCodeToHandleMap.end()) {
+            return it->second;
+        }
         _MozJSCreateFunction(raw, &fun);
         _funcs.emplace_back(_context, fun.get());
-        return _funcs.size();
+        _funcCodeToHandleMap.emplace(raw, _funcs.size());
+        return ScriptingFunction(_funcs.size());
     });
 }
 
diff --git a/src/mongo/scripting/mozjs/implscope.h b/src/mongo/scripting/mozjs/implscope.h
index b842ae3cbef..86aa6c5dd05 100644
--- a/src/mongo/scripting/mozjs/implscope.h
+++ b/src/mongo/scripting/mozjs/implscope.h
@@ -67,6 +67,7 @@
 #include "mongo/scripting/mozjs/timestamp.h"
 #include "mongo/scripting/mozjs/uri.h"
 #include "mongo/stdx/unordered_set.h"
+#include "mongo/util/string_map.h"
 
 namespace mongo {
 namespace mozjs {
@@ -411,6 +412,7 @@ private:
     WrapType<GlobalInfo> _globalProto;
     JS::HandleObject _global;
     std::vector<JS::PersistentRootedValue> _funcs;
+    StringMap<ScriptingFunction> _funcCodeToHandleMap;
     InternedStringTable _internedStrings;
     Status _killStatus;
     mutable Mutex _mutex = MONGO_MAKE_LATCH("MozJSImplScope::_mutex");