Fixed bug where fleetd-chrome sent multiple read requests to Fleet server at the same time. (#18777)

#18775 
Fixed bug where fleetd-chrome sent multiple read requests to Fleet
server at the same time.

# Checklist for submitter

<!-- Note that API documentation changes are now addressed by the
product design team. -->

- [x] Changes file added for user-visible changes in `changes/`,
`orbit/changes/` or `ee/fleetd-chrome/changes`.
See [Changes
files](https://fleetdm.com/docs/contributing/committing-changes#changes-files)
for more information.
- [x] Manual QA for all new/changed functionality

ee/fleetd-chrome/changes/18775-2-main-threads

@@ -0,0 +1 @@
+Fixed bug where fleetd-chrome sent multiple read requests to Fleet server at the same time.

ee/fleetd-chrome/package-lock.json

@@ -8,6 +8,7 @@
       "name": "fleetd-for-chrome",
       "version": "1.3.0",
       "dependencies": {
+        "async-mutex": "^0.5.0",
         "dotenv": "^16.0.3",
         "wa-sqlite": "github:rhashimoto/wa-sqlite#v0.9.11"
       },
@@ -2066,6 +2067,14 @@
         "node": "*"
       }
     },
+    "node_modules/async-mutex": {
+      "version": "0.5.0",
+      "resolved": "https://registry.npmjs.org/async-mutex/-/async-mutex-0.5.0.tgz",
+      "integrity": "sha512-1A94B18jkJ3DYq284ohPxoXbfTA5HsQ7/Mf4DEhcyLx3Bz27Rh59iScbB6EPiP+B+joue6YCxcMXSbFC1tZKwA==",
+      "dependencies": {
+        "tslib": "^2.4.0"
+      }
+    },
     "node_modules/asynckit": {
       "version": "0.4.0",
       "resolved": "https://registry.npmjs.org/asynckit/-/asynckit-0.4.0.tgz",
@@ -8137,8 +8146,7 @@
     "node_modules/tslib": {
       "version": "2.5.0",
       "resolved": "https://registry.npmjs.org/tslib/-/tslib-2.5.0.tgz",
-      "integrity": "sha512-336iVw3rtn2BUK7ORdIAHTyxHGRIHVReokCR3XjbckJMK7ms8FysBfhLR8IXnAgy7T0PTPNBWKiH514FOW/WSg==",
-      "dev": true
+      "integrity": "sha512-336iVw3rtn2BUK7ORdIAHTyxHGRIHVReokCR3XjbckJMK7ms8FysBfhLR8IXnAgy7T0PTPNBWKiH514FOW/WSg=="
     },
     "node_modules/type-detect": {
       "version": "4.0.8",

ee/fleetd-chrome/package.json

@@ -3,6 +3,7 @@
   "description": "Extension for Fleetd on ChromeOS",
   "version": "1.3.0",
   "dependencies": {
+    "async-mutex": "^0.5.0",
     "dotenv": "^16.0.3",
     "wa-sqlite": "github:rhashimoto/wa-sqlite#v0.9.11"
   },

ee/fleetd-chrome/src/background.ts

@@ -1,4 +1,5 @@
 import VirtualDatabase from "./db";
+import {Mutex, withTimeout, tryAcquire, E_ALREADY_LOCKED} from 'async-mutex';
 
 // ENV Vars
 declare var FLEET_URL: string;
@@ -236,6 +237,12 @@ class NodeInvalidError extends Error {
   }
 }
 
+// We use a mutex to ensure that only one instance of main is running at a time.
+const mutexWithTimeout = withTimeout(new Mutex(), 60 * 1000) // 60 second timeout
+async function runExclusive(callback: () => Promise<void>) {
+  await tryAcquire(mutexWithTimeout).runExclusive(callback)
+}
+
 // QUESTION maybe we should use one of the persistence mechanisms described in
 // https://stackoverflow.com/a/66618269/491710? The "offscreen API" mechanism might be useful. On
 // the other hand, this seems to work decently well and adding the complexity might not be worth it.
@@ -247,16 +254,20 @@ class NodeInvalidError extends Error {
 let mainTimeout: ReturnType<typeof setTimeout>;
 const mainLoop = async () => {
   try {
-    await main();
-    clearTimeout(mainTimeout);
-    mainTimeout = setTimeout(mainLoop, 10 * 1000);
+    await runExclusive(main);
   } catch (err) {
+    if (err === E_ALREADY_LOCKED) {
+      console.info("'main' mutex already locked, skipping run")
+      return
+    }
     console.error(err);
     if (err.message === MEMORY_RUNTIME_ERROR_MESSAGE) {
       console.info("Restarting DB after wa-sqlite RuntimeError")
       await initDB();
     }
   }
+  clearTimeout(mainTimeout);
+  mainTimeout = setTimeout(mainLoop, 10 * 1000);
 };
 mainLoop();