Don't run --extern-pre-js or --extern-post-js code on pthread workers (#21750)

This means, for example, that folks can call the module constructor as
part of `--extern-post-js` without accidentally creating an extra module
instance on each thread.

For an example of this pattern see
test_pthread_offset_converter_modularize.

Although this is minor code size regression I'm about to followup with
a major refactor that saves a lot more code: #21701

Author: sbc100

ChangeLog.md

@@ -21,6 +21,8 @@ See docs/process.md for more on how version tagging works.
 3.1.58 (in development)
 -----------------------
 - Enable use of `::` to escape port option separator (#21710)
+- In multi-threaded builds `--extern-pre-js` and `--extern-post-js` code is
+  now only run on the main thread, and not on each of the workers. (#21750)
 
 3.1.57 - 04/10/24
 -----------------

src/runtime_init_memory.js

@@ -20,6 +20,9 @@ assert(INITIAL_MEMORY >= {{{STACK_SIZE}}}, 'INITIAL_MEMORY should be larger than
 #if PTHREADS
 if (ENVIRONMENT_IS_PTHREAD) {
   wasmMemory = Module['wasmMemory'];
+#if ASSERTIONS
+  assert(wasmMemory, 'wasmMemory not set on incomming module object');
+#endif
 } else {
 #endif // PTHREADS
 

src/shell.js

@@ -119,7 +119,14 @@ if (Module['ENVIRONMENT']) {
 // 3) We could be an application pthread running in a worker. (ENVIRONMENT_IS_WORKER == true and ENVIRONMENT_IS_PTHREAD == true)
 
 // ENVIRONMENT_IS_PTHREAD=true will have been preset in worker.js. Make it false in the main runtime thread.
-var ENVIRONMENT_IS_PTHREAD = Module['ENVIRONMENT_IS_PTHREAD'] || false;
+var ENVIRONMENT_IS_PTHREAD = globalThis['ENVIRONMENT_IS_PTHREAD'] || false;
+
+#if MODULARIZE && ASSERTIONS
+if (ENVIRONMENT_IS_PTHREAD) {
+  assert(!globalThis.moduleLoaded, 'module should only be loaded once on each pthread worker');
+  globalThis.moduleLoaded = true;
+}
+#endif
 #endif
 
 #if WASM_WORKERS

src/worker.js

@@ -192,8 +192,9 @@ function handleMessage(e) {
       Module['workerID'] = e.data.workerID;
 #endif
 
-#if !MINIMAL_RUNTIME || MODULARIZE
-      {{{ makeAsmImportsAccessInPthread('ENVIRONMENT_IS_PTHREAD') }}} = true;
+#if !MINIMAL_RUNTIME
+      // Set ENVIRONMENT_IS_PTHREAD before importing the main script
+      globalThis['ENVIRONMENT_IS_PTHREAD'] = true;
 #endif
 
 #if MODULARIZE && EXPORT_ES6

test/other/metadce/test_metadce_minimal_pthreads.gzsize

@@ -1 +1 @@
-6098
+6107

test/other/metadce/test_metadce_minimal_pthreads.jssize

@@ -1 +1 @@
-13448
+13461

tools/js_manipulation.py

@@ -44,7 +44,7 @@ def add_files_pre_js(pre_js_list, files_pre_js):
   utils.write_file(pre, '''
     // All the pre-js content up to here must remain later on, we need to run
     // it.
-    if (Module['ENVIRONMENT_IS_PTHREAD'] || Module['$ww']) Module['preRun'] = [];
+    if (globalThis['ENVIRONMENT_IS_PTHREAD'] || Module['$ww']) Module['preRun'] = [];
     var necessaryPreJSTasks = Module['preRun'].slice();
   ''')
   utils.write_file(post, '''

tools/link.py

@@ -721,6 +721,13 @@ def phase_linker_setup(options, state, newargs):
   options.extern_pre_js = read_js_files(options.extern_pre_js)
   options.extern_post_js = read_js_files(options.extern_post_js)
 
+  if settings.PTHREADS:
+    # Don't run extern pre/post code on pthreads.
+    if options.extern_pre_js:
+      options.extern_pre_js = 'if (typeof ENVIRONMENT_IS_PTHREAD == "undefined") {' + options.extern_pre_js + '}'
+    if options.extern_post_js:
+      options.extern_post_js = 'if (typeof ENVIRONMENT_IS_PTHREAD == "undefined") {' + options.extern_post_js + '}'
+
   # TODO: support source maps with js_transform
   if options.js_transform and settings.GENERATE_SOURCE_MAP:
     logger.warning('disabling source maps because a js transform is being done')