chore: OliveTin 3k progress

frontend/js/Mutex.js

@@ -0,0 +1,24 @@
+export class Mutex {
+  constructor() {
+    this._locked = false;
+    this._waiting = [];
+  }
+
+  lock() {
+    const unlock = () => {
+      const next = this._waiting.shift();
+      if (next) {
+        next(unlock);
+      } else {
+        this._locked = false;
+      }
+    };
+
+    if (this._locked) {
+      return new Promise(resolve => this._waiting.push(resolve)).then(() => unlock);
+    } else {
+      this._locked = true;
+      return Promise.resolve(unlock);
+    }
+  }
+}