test: reduce the allocation size in test-worker-arraybuffer-zerofill

Test has been flaky with timeouts in CI. This is possibly due to the
repeated large allocations on the main thread. This commit reduces the
allocation size and makes a number of other cleanups. The main goal
is to hopefully make this test more reliable / not-flaky.
Also move the test to sequential. The frequent large allocations
could be causing the test to be flaky if run parallel to other tests.
PR-URL: #54839
Refs: #52274
Reviewed-By: Yagiz Nizipli <yagiz@nizipli.com>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>

Author: jasnell

test/parallel/test-worker-arraybuffer-zerofill.js

@@ -0,0 +1,43 @@
+'use strict';
+require('../common');
+constCountdown=require('../common/countdown');
+constassert=require('assert');
+const{ Worker }=require('worker_threads');
+const{ describe, it, mock }=require('node:test');
+
+describe('Allocating uninitialized ArrayBuffers ...',()=>{
+it('...should not affect zero-fill in other threads',()=>{
+constw=newWorker(`
+ const { parentPort } = require('worker_threads');
+
+ function post() {
+ const uint32array = new Uint32Array(64);
+ parentPort.postMessage(uint32array.reduce((a, b) => a + b));
+ }
+
+ setInterval(post, 0);
+ `,{eval: true});
+
+constfn=mock.fn(()=>{
+// Continuously allocate memory in the main thread. The allocUnsafe
+// here sets a scope internally that indicates that the memory should
+// not be initialized. While this is happening, the other thread is
+// also allocating buffers that must remain zero-filled. The purpose
+// of this test is to ensure that the scope used to determine whether
+// to zero-fill or not does not impact the other thread.
+setInterval(()=>Buffer.allocUnsafe(32*1024*1024),0).unref();
+});
+
+w.on('online',fn);
+
+constcountdown=newCountdown(100,()=>{
+w.terminate();
+assert(fn.mock.calls.length>0);
+});
+
+w.on('message',(sum)=>{
+assert.strictEqual(sum,0);
+if(countdown.remaining)countdown.dec();
+});
+});
+});