Move middleware utils into server/utils

server/utils/createMutex.js

@@ -0,0 +1,21 @@
+function createMutex(doWork) {
+  const mutex = Object.create(null);
+
+  return (key, payload, callback) => {
+    if (mutex[key]) {
+      mutex[key].push(callback);
+    } else {
+      mutex[key] = [callback];
+
+      doWork(payload, (error, value) => {
+        mutex[key].forEach(callback => {
+          callback(error, value);
+        });
+
+        delete mutex[key];
+      });
+    }
+  };
+}
+
+module.exports = createMutex;