Allow pthread programs to run without SharedArrayBuffer (#22710)

As long as they don't actually try to start any threads there is no
reason to prevent them from running/starting.

Such programs will now instead fail when they first try to create
a thread.

This is useful for programs that are built with threading support but
might also want to run in environments without SharedArrayBuffer,
e.g. when deployed without COOP/COEP.

Author: sbc100

src/preamble_minimal.js

@@ -93,10 +93,6 @@ else {
 if (!ENVIRONMENT_IS_PTHREAD) {
 #endif
 
-#if ASSERTIONS && SHARED_MEMORY
-assert(wasmMemory.buffer instanceof SharedArrayBuffer, 'requested a shared WebAssembly.Memory but the returned buffer is not a SharedArrayBuffer, indicating that while the browser has SharedArrayBuffer it does not have WebAssembly threads support - you may need to set a flag');
-#endif
-
 updateMemoryViews();
 
 #if PTHREADS

src/runtime_init_memory.js

@@ -45,15 +45,6 @@ if (!ENVIRONMENT_IS_PTHREAD) {
       'index': 'i64',
 #endif
     });
-#if SHARED_MEMORY
-    if (!(wasmMemory.buffer instanceof SharedArrayBuffer)) {
-      err('requested a shared WebAssembly.Memory but the returned buffer is not a SharedArrayBuffer, indicating that while the browser has SharedArrayBuffer it does not have WebAssembly threads support - you may need to set a flag');
-      if (ENVIRONMENT_IS_NODE) {
-        err('(on node you may need: --experimental-wasm-threads --experimental-wasm-bulk-memory and/or recent version)');
-      }
-      throw Error('bad memory');
-    }
-#endif
   }
 
   updateMemoryViews();

test/test_other.py

@@ -12071,6 +12071,18 @@ def test_pthread_hello(self, args):
   def test_pthread_relocatable(self):
     self.do_run_in_out_file_test('hello_world.c', emcc_args=['-sRELOCATABLE'])
 
+  @node_pthreads
+  def test_pthread_unavailable(self):
+    # Run a simple hello world program that uses pthreads
+    self.emcc_args += ['-sPROXY_TO_PTHREAD', '-sEXIT_RUNTIME']
+    self.do_run_in_out_file_test('hello_world.c')
+
+    # Now run the same program but with SharedArrayBuffer undefined, it should run
+    # fine and then fail on the first call to pthread_create.
+    create_file('pre.js', 'SharedArrayBuffer = undefined\n')
+    expected = 'pthread_create: environment does not support SharedArrayBuffer, pthreads are not available'
+    self.do_runf('hello_world.c', expected, assert_returncode=NON_ZERO, emcc_args=['--pre-js=pre.js'])
+
   def test_stdin_preprocess(self):
     create_file('temp.h', '#include <string>')
     outputStdin = self.run_process([EMCC, '-x', 'c++', '-dM', '-E', '-'], input="#include <string>", stdout=PIPE).stdout