Fix default pthread stack size when running in worker. (#19577)

Fixes: #19573

Author: sbc100

src/library_pthread.js

@@ -19,9 +19,6 @@
 #if BUILD_AS_WORKER
 #error "pthreads + BUILD_AS_WORKER require separate modes that don't work together, see https://github.com/emscripten-core/emscripten/issues/8854"
 #endif
-#if PROXY_TO_WORKER
-#error "--proxy-to-worker is not supported with -pthread! Use the option -sPROXY_TO_PTHREAD if you want to run the main thread of a multithreaded application in a web worker."
-#endif
 #if EVAL_CTORS
 #error "EVAL_CTORS is not compatible with pthreads yet (passive segments)"
 #endif

system/lib/pthread/emscripten_thread_init.c

@@ -16,7 +16,10 @@ void _emscripten_thread_init(pthread_t ptr,
                              int default_stacksize,
                              int start_profiling) {
   __set_thread_state(ptr, is_main, is_runtime, can_block);
-  if (is_main && default_stacksize) {
+  // Set `__default_stacksize` just once when the main runtime thread is
+  // started.  The value of `DEFAULT_PTHREAD_STACK_SIZE` is passed in here as
+  // `default_stacksize`.
+  if (is_runtime && default_stacksize) {
     __default_stacksize = default_stacksize;
   }
 #ifndef NDEBUG

test/other/test_default_pthread_stack_size.c

@@ -14,5 +14,6 @@ int main() {
   pthread_attr_getstacksize(&attr, &stacksize);
   printf("expected: %d, actual: %zu\n", EXPECTED_STACK_SIZE, stacksize);
   assert(stacksize == EXPECTED_STACK_SIZE);
+  printf("done\n");
   return 0;
 }

test/other/test_default_pthread_stack_size.out

@@ -0,0 +1 @@
+done

test/test_other.py

@@ -12366,11 +12366,15 @@ def test_default_pthread_stack_size(self):
 
     # Same again with pthreads enabled
     self.setup_node_pthreads()
-    self.do_runf(test_file('other/test_default_pthread_stack_size.c'))
+    self.do_other_test('test_default_pthread_stack_size.c')
 
     # Same again but with a custom stack size
     self.emcc_args += ['-DEXPECTED_STACK_SIZE=1024', '-sDEFAULT_PTHREAD_STACK_SIZE=1024']
-    self.do_runf(test_file('other/test_default_pthread_stack_size.c'))
+    self.do_other_test('test_default_pthread_stack_size.c')
+
+    # Same again but with a --proxy-to-worker
+    self.emcc_args += ['--proxy-to-worker']
+    self.do_other_test('test_default_pthread_stack_size.c')
 
   def test_emscripten_set_immediate(self):
     self.do_runf(test_file('emscripten_set_immediate.c'))