test: avoid worker in shared value conveyor test

V8 no longer supports JSON.parse on worker isolates while the shared
string table is enabled. Since --harmony-struct enables that table and
Node workers parse process.config during bootstrap,
use direct MessageChannel instead of a worker.

Signed-Off-By: Michaël Zasso <targos@protonmail.com>

Author: targos

test/parallel/test-experimental-shared-value-conveyor.js

@@ -2,26 +2,22 @@
 const common = require('../common');
 const assert = require('assert');
 const { spawnSync } = require('child_process');
-const { Worker, parentPort } = require('worker_threads');
+const { MessageChannel } = require('worker_threads');
 
 if (process.env.TEST_CHILD_PROCESS === '1') {
-  // Do not use isMainThread so that this test itself can be run inside a Worker.
-  if (!process.env.HAS_STARTED_WORKER) {
-    process.env.HAS_STARTED_WORKER = 1;
-    const m = new globalThis.SharedArray(16);
+  // --harmony-struct implies --shared-string-table. V8 currently does not
+  // support JSON.parse in worker isolates with that flag, and Node workers
+  // parse process.config during bootstrap.
+  const m = new globalThis.SharedArray(16);
+  const { port1, port2 } = new MessageChannel();
 
-    const worker = new Worker(__filename);
-    worker.once('message', common.mustCall((message) => {
-      assert.strictEqual(message, m);
-    }));
+  port1.once('message', common.mustCall((message) => {
+    assert.strictEqual(message, m);
+    port1.close();
+    port2.close();
+  }));
 
-    worker.postMessage(m);
-  } else {
-    parentPort.once('message', common.mustCall((message) => {
-      // Simple echo.
-      parentPort.postMessage(message);
-    }));
-  }
+  port2.postMessage(m);
 } else {
   if (process.config.variables.v8_enable_pointer_compression === 1) {
     common.skip('--harmony-struct cannot be used with pointer compression');