feat(engine): parallelize code execution (#80)

## How does this PR impact the user?

This PR will speed up code execution in the engine by parallelizing it.

## Description

- [x] parallelize code execution

Below are the results on some synthetic test with 10 sequential vs 10
parallel runs.

### Before

<img width="475" alt="Screenshot 2024-11-17 at 11 44 26"
src="https://github.com/user-attachments/assets/4556f7eb-1c46-4691-8c90-4f1e897ccbbf">

### After: 5x win

<img width="458" alt="Screenshot 2024-11-17 at 11 43 36"
src="https://github.com/user-attachments/assets/e2e3cf13-0f73-424f-8ca5-80f27fca8130">

## Limitations

N/A

## Checklist

- [x] my PR is focused and contains one wholistic change
- [ ] I have added screenshots or screen recordings to show the changes

other/CodeRunner.spec.ts

@@ -76,4 +76,14 @@ describe("CodeRunner", () => {
     // @ts-expect-error - we're testing a property that doesn't exist on the Array prototype
     expect([].foo).toBeUndefined();
   });
+
+  it("can run multiple scripts in parallel", async () => {
+    const scripts: string[] = [];
+    for (let i = 0; i < 10; i++) {
+      scripts.push(`for (let i = 0; i < 10_000_000; ++i) {}; 1 + ${i}`);
+    }
+    const codeRunner = new CodeRunner();
+    const results = await Promise.all(scripts.map(script => codeRunner.runCode(script)));
+    expect(results).toEqual([1, 2, 3, 4, 5, 6, 7, 8, 9, 10]);
+  });
 });

server/plugins/engine.ts

@@ -9,12 +9,7 @@ const GAME_STEP_INTERVAL_MS = 250;
 const WORLD_SIZE = 600;
 
 export const WORLD_REF = { world: new World ({ width: WORLD_SIZE, height: WORLD_SIZE }) };
-const codeRunner = new CodeRunner();
-
-async function runBot(code: string) {
-  const result = await codeRunner.runCode(code);
-  return JSON.parse(result);
-}
+const codeRunners = new Array(10).fill(0).map(() => new CodeRunner());
 
 type RunBotArgs = {
   bots: botCodeStore.BotCodes;
@@ -33,24 +28,29 @@ async function runBots({ bots, world, prevBotState, botApi }: RunBotArgs) {
   const state = world.getState();
   const botArray = Object.values(bots);
 
-  const botActions = [];
-  for (const bot of botArray) {
+  const preparedBotCodes = botArray.map(bot => prepareBotCode({
+    bot,
+    botInfo: bots,
+    state,
+    prevBotState,
+    botApi,
+  }));
+
+  const botActions = await Promise.all(preparedBotCodes.map(async (preparedCode, i) => {
+    const codeRunner = codeRunners[i % codeRunners.length];
+    if (!codeRunner) {
+      throw new Error("unexpected: codeRunner is undefined");
+    }
+
     try {
-      const preparedCode = prepareBotCode({
-        bot,
-        botInfo: bots,
-        state,
-        prevBotState,
-        botApi,
-      });
-      const actions = await runBot(preparedCode);
-      botActions.push(actions);
+      const result = await codeRunner.runCode(preparedCode);
+      return JSON.parse(result);
     } catch (err) {
       // TODO(yurij): notify user that their bot crashed
       console.error(err);
-      botActions.push([]);
+      return [];
     }
-  };
+  }));
 
   for (const [i, actions] of botActions.entries()) {
     const botId = botArray[i]?.id;