Image Optimization - Create new ImagePool for each batch (#470)

We have been having issues with the image optimization script consuming egregious amounts of memory and failing CI as a result.

This PR changes the script so that we use a new `ImagePool` to process each batch of images.

Co-authored-by: Amy <a258wang@uwaterloo.ca>
Reviewed-on: #470
Reviewed-by: Shahan Neda <snedadah@csclub.uwaterloo.ca>

scripts/optimize-images.ts

@@ -44,12 +44,14 @@ export async function optimizeImages() {
 
   // maximum number of workers is 8 in order to avoid running out of memory
   const numberOfWorkers = Math.min(cpus().length, 8);
-  const imagePool = new ImagePool(numberOfWorkers);
 
   // process smaller batches in order to reduce memory usage
   const batchSize = 32;
 
   for (let i = 0; i < imagePaths.length; i += batchSize) {
+    // use a new ImagePool for each batch to reduce memory usage
+    const imagePool = new ImagePool(numberOfWorkers);
+
     await Promise.all(
       imagePaths.slice(i, i + batchSize).map(async (imagePath) => {
         const imageStartTime = Date.now();
@@ -108,9 +110,9 @@ export async function optimizeImages() {
         );
       })
     );
-  }
 
-  await imagePool.close();
+    await imagePool.close();
+  }
 
   console.log(`TOTAL DURATION: ${getElapsedSeconds(startTime)}s`);
 }