[MODULARIZE=instance] Ensure init function is only called once (#24329)

We were calling init() more than once on threads.

Author: sbc100

.circleci/config.yml

@@ -814,7 +814,7 @@ jobs:
             instance.test_EXPORTED_RUNTIME_METHODS
             instance.test_ccall
             instance.test_dylink_basics*
-            instance.test_Module_dynamicLibraries
+            instance.test_Module_dynamicLibraries*
             esm_integration.test_fs_js_api*
             esm_integration.test_inlinejs3
             esm_integration.test_embind_val_basics

src/postamble.js

@@ -302,7 +302,14 @@ function preInit() {
 #if MODULARIZE == 'instance'
 // In MODULARIZE=instance mode we delay most of the initialization work until
 // the `init` function is called.
+#if ASSERTIONS
+var initCalled = false;
+#endif
 export default async function init(moduleArg = {}) {
+#if ASSERTIONS
+  assert(!initCalled);
+  initCalled = true;
+#endif
   Object.assign(Module, moduleArg);
   processModuleArgs();
 #if WASM_ESM_INTEGRATION
@@ -322,7 +329,12 @@ if (ENVIRONMENT_IS_PTHREAD) await init()
 
 #if ENVIRONMENT_MAY_BE_NODE
 // When run as the main script under node we run `init` immediately.
-if (ENVIRONMENT_IS_NODE) {
+if (ENVIRONMENT_IS_NODE
+#if PTHREADS || WASM_WORKERS
+&& !{{{ ENVIRONMENT_IS_WORKER_THREAD() }}}
+#endif
+)
+{
   const url = await import('url');
   const isMainModule = url.pathToFileURL(process.argv[1]).href === import.meta.url;
   if (isMainModule) await init();