From 68468fadb349dd54f64f0cccca2e3b091c6374a6 Mon Sep 17 00:00:00 2001
From: Sam Rose <hello@samwho.dev>
Date: Thu, 4 Jan 2024 10:10:00 +0000
Subject: [PATCH] Add an extra JS execution time limit check to prevent
 creating unnecesary VM context.

---
 packages/backend-core/src/timers/timers.ts | 2 +-
 packages/server/src/jsRunner.ts            | 5 ++++-
 2 files changed, 5 insertions(+), 2 deletions(-)

diff --git a/packages/backend-core/src/timers/timers.ts b/packages/backend-core/src/timers/timers.ts
index 9de57af7f1..9121c576cd 100644
--- a/packages/backend-core/src/timers/timers.ts
+++ b/packages/backend-core/src/timers/timers.ts
@@ -50,7 +50,7 @@ export class ExecutionTimeTracker {
     return this.totalTimeMs
   }
 
-  private checkLimit() {
+  checkLimit() {
     if (this.totalTimeMs > this.limitMs) {
       throw new ExecutionTimeoutError(
         `Execution time limit of ${this.limitMs}ms exceeded: ${this.totalTimeMs}ms`
diff --git a/packages/server/src/jsRunner.ts b/packages/server/src/jsRunner.ts
index ab0381a399..a9dcd506d7 100644
--- a/packages/server/src/jsRunner.ts
+++ b/packages/server/src/jsRunner.ts
@@ -18,13 +18,16 @@ export function init() {
             bbCtx.jsExecutionTracker =
               timers.ExecutionTimeTracker.withLimit(perRequestLimit)
           }
-          track = bbCtx.jsExecutionTracker.track.bind(bbCtx.jsExecutionTracker)
           span?.addTags({
             js: {
               limitMS: bbCtx.jsExecutionTracker.limitMs,
               elapsedMS: bbCtx.jsExecutionTracker.elapsedMS,
             },
           })
+          // We call checkLimit() here to prevent paying the cost of creating
+          // a new VM context below when we don't need to.
+          bbCtx.jsExecutionTracker.checkLimit()
+          track = bbCtx.jsExecutionTracker.track.bind(bbCtx.jsExecutionTracker)
         }
       }