perf: prevent duplicate cache refresh

package.json

@@ -35,6 +35,7 @@
     "start-s": "tsx src/server.ts"
   },
   "dependencies": {
+    "await-lock": "^2.2.2",
     "axios": "^0.27.2",
     "axios-retry": "^3.2.5",
     "cheerio": "^1.0.0-rc.11",

src/server.ts

@@ -10,6 +10,7 @@ import { Command } from "commander";
 import { bin, version } from "../package.json";
 import _ from "lodash";
 import { readFileSync } from "fs";
+import AwaitLock from "await-lock";
 
 const app = express();
 
@@ -84,6 +85,8 @@ const contestsCache: {
     lastUpdate: 0
 };
 
+const lock = new AwaitLock();
+
 function icsPostProcess(value: string)
 {
     return value
@@ -104,17 +107,30 @@ function icsPostProcess(value: string)
         );
 }
 
-async function getIcs(lang: string, ojs: string[])
+async function checkCache()
 {
-    if(contestsCache.lastUpdate < Date.now() - 1000 * 60 * 5)
+    await lock.acquireAsync();
+    try
+    {
+        if(contestsCache.lastUpdate < Date.now() - 1000 * 60 * 5)
+        {
+            const c = await new Lscontests({ days: -1 }).getContests();
+            contestsCache.contests = _.uniqBy(contestsCache.contests.concat(c.running.concat(c.upcoming)), JSON.stringify);
+            contestsCache.contests = contestsCache.contests.filter(
+                c => c.endTime.getTime() - c.startTime.getTime() < 1000 * 60 * 60 * 24 * 2
+            ); // ignore too long contests
+            contestsCache.lastUpdate = Date.now();
+        }
+    }
+    finally
     {
-        const c = await new Lscontests({ days: -1 }).getContests();
-        contestsCache.contests = _.uniqBy(contestsCache.contests.concat(c.running.concat(c.upcoming)), JSON.stringify);
-        contestsCache.contests = contestsCache.contests.filter(
-            c => c.endTime.getTime() - c.startTime.getTime() < 1000 * 60 * 60 * 24 * 2
-        ); // ignore too long contests
-        contestsCache.lastUpdate = Date.now();
+        lock.release();
     }
+}
+
+async function getIcs(lang: string, ojs: string[])
+{
+    await checkCache();
 
     const contests = contestsCache.contests.filter(c => ojs.some(oj => c.ojName === alloj[oj].name));
     const langDict = await getLangDict(lang);

yarn.lock

@@ -499,6 +499,11 @@ asynckit@^0.4.0:
   resolved "https://registry.yarnpkg.com/asynckit/-/asynckit-0.4.0.tgz#c79ed97f7f34cb8f2ba1bc9790bcc366474b4b79"
   integrity sha512-Oei9OH4tRh0YqU3GxhX79dM/mwVgvbZJaSNaRk+bshkj0S5cfHcgYakreBjrHwatXKbz+IoIdYLxrKim2MjW0Q==
 
+await-lock@^2.2.2:
+  version "2.2.2"
+  resolved "https://registry.yarnpkg.com/await-lock/-/await-lock-2.2.2.tgz#a95a9b269bfd2f69d22b17a321686f551152bcef"
+  integrity sha512-aDczADvlvTGajTDjcjpJMqRkOF6Qdz3YbPZm/PyW6tKPkx2hlYBzxMhEywM/tU72HrVZjgl5VCdRuMlA7pZ8Gw==
+
 axios-retry@^3.2.5:
   version "3.3.1"
   resolved "https://registry.yarnpkg.com/axios-retry/-/axios-retry-3.3.1.tgz#47624646138aedefbad2ac32f226f4ee94b6dcab"