Enable pthread mutex/cond/rw_lock to be used in Wasm Workers

ChangeLog.md

@@ -30,6 +30,8 @@ See docs/process.md for more on how version tagging works.
   This is an extension of #26336 which removed many of them.  These APIs were
   not previously functional under Wasm Workers, but if there is strong use case
   it may be possible to enable them in future. (#26487)
+- Pthread mutex/cond/rwlock primitives now work from with Wasm Workers (and
+  between Wasm Workers and pthreads). (#26510)
 
 5.0.3 - 03/14/26
 ----------------

site/source/docs/api_reference/wasm_workers.rst

@@ -89,13 +89,15 @@ Pthreads and Wasm Workers share several similarities:
  * Both can use emscripten_futex_wait/wake API,
  * Both can use GCC __sync_* Atomics API,
  * Both can use C11 and C++11 Atomics APIs,
+ * Both can use pthread_mutex/pthread_cond/pthread_rwlock/pthread_once APIs.
  * Both types of threads have a local stack.
  * Both types of threads have thread-local storage (TLS) support via ``thread_local`` (C++11),
    ``_Thread_local`` (C11) and ``__thread`` (GNU11) keywords.
  * Both types of threads support TLS via explicitly linked in Wasm globals (see
    ``test/wasm_worker/wasm_worker_tls_wasm_assembly.c/.S`` for example code)
  * Both types of threads have a concept of a thread ID (``pthread_self()`` for pthreads,
-   ``emscripten_wasm_worker_self_id()`` for Wasm Workers)
+   ``emscripten_wasm_worker_self_id()`` for Wasm Workers).  `gettid()` works in
+   both contexts so is more portable.
  * Both types of threads can perform an event-based and an infinite loop programming model.
  * Both can use ``EM_ASM`` and ``EM_JS`` API to execute JS code on the calling thread.
  * Both can call out to JS library functions (linked in with ``--js-library`` directive) to

src/lib/libatomic.js

@@ -161,4 +161,23 @@ addToLibrary({
     navigator['hardwareConcurrency'],
 
   emscripten_atomics_is_lock_free: (width) => Atomics.isLockFree(width),
+
+#if (ASSERTIONS || !ALLOW_BLOCKING_ON_MAIN_THREAD) && !MINIMAL_RUNTIME
+  emscripten_check_blocking_allowed__deps: ['$warnOnce'],
+#endif
+  emscripten_check_blocking_allowed: () => {
+#if (ASSERTIONS || !ALLOW_BLOCKING_ON_MAIN_THREAD) && !MINIMAL_RUNTIME
+#if ENVIRONMENT_MAY_BE_NODE
+    if (ENVIRONMENT_IS_NODE) return;
+#endif
+
+    if (ENVIRONMENT_IS_WORKER) return; // Blocking in a worker/pthread is fine.
+
+    warnOnce('Blocking on the main thread is very dangerous, see https://emscripten.org/docs/porting/pthreads.html#blocking-on-the-main-browser-thread');
+#if !ALLOW_BLOCKING_ON_MAIN_THREAD
+    abort('Blocking on the main thread is not allowed by default. See https://emscripten.org/docs/porting/pthreads.html#blocking-on-the-main-browser-thread');
+#endif
+
+#endif
+  },
 });

src/lib/libpthread.js

@@ -904,25 +904,6 @@ var LibraryPThread = {
     return spawnThread(threadParams);
   },
 
-#if (ASSERTIONS || !ALLOW_BLOCKING_ON_MAIN_THREAD) && !MINIMAL_RUNTIME
-  emscripten_check_blocking_allowed__deps: ['$warnOnce'],
-#endif
-  emscripten_check_blocking_allowed: () => {
-#if (ASSERTIONS || !ALLOW_BLOCKING_ON_MAIN_THREAD) && !MINIMAL_RUNTIME
-#if ENVIRONMENT_MAY_BE_NODE
-    if (ENVIRONMENT_IS_NODE) return;
-#endif
-
-    if (ENVIRONMENT_IS_WORKER) return; // Blocking in a worker/pthread is fine.
-
-    warnOnce('Blocking on the main thread is very dangerous, see https://emscripten.org/docs/porting/pthreads.html#blocking-on-the-main-browser-thread');
-#if !ALLOW_BLOCKING_ON_MAIN_THREAD
-    abort('Blocking on the main thread is not allowed by default. See https://emscripten.org/docs/porting/pthreads.html#blocking-on-the-main-browser-thread');
-#endif
-
-#endif
-  },
-
   // This function is called by a pthread to signal that exit() was called and
   // that the entire process should exit.
   // This function is always called from a pthread, but is executed on the

system/lib/libc/musl/src/temp/__randname.c

@@ -11,7 +11,7 @@ char *__randname(char *template)
 	unsigned long r;
 
 	__clock_gettime(CLOCK_REALTIME, &ts);
-	r = ts.tv_sec + ts.tv_nsec + __pthread_self()->tid * 65537UL;
+	r = ts.tv_sec + ts.tv_nsec + CURRENT_THREAD_ID * 65537UL;
 
 	/* XXX EMSCRIPTEN: avoid repeating the same result when __clock_gettime does not change between calls. */
 	static unsigned int counter = 0;

system/lib/libc/musl/src/thread/pthread_cond_timedwait.c

@@ -82,7 +82,7 @@ int __pthread_cond_timedwait(pthread_cond_t *restrict c, pthread_mutex_t *restri
 	}
 #endif
 
-	if ((m->_m_type&15) && (m->_m_lock&INT_MAX) != __pthread_self()->tid)
+	if ((m->_m_type&15) && (m->_m_lock&INT_MAX) != CURRENT_THREAD_ID)
 		return EPERM;
 
 	if (ts && ts->tv_nsec >= 1000000000UL)

system/lib/libc/musl/src/thread/pthread_mutex_consistent.c

@@ -7,7 +7,7 @@ int pthread_mutex_consistent(pthread_mutex_t *m)
 	int own = old & 0x3fffffff;
 	if (!(m->_m_type & 4) || !own || !(old & 0x40000000))
 		return EINVAL;
-	if (own != __pthread_self()->tid)
+	if (own != CURRENT_THREAD_ID)
 		return EPERM;
 	a_and(&m->_m_lock, ~0x40000000);
 	return 0;

system/lib/libc/musl/src/thread/pthread_mutex_timedlock.c

@@ -87,12 +87,12 @@ int __pthread_mutex_timedlock(pthread_mutex_t *restrict m, const struct timespec
 		if (!own && (!r || (type&4)))
 			continue;
 		if ((type&3) == PTHREAD_MUTEX_ERRORCHECK
-		    && own == __pthread_self()->tid)
+		    && own == CURRENT_THREAD_ID)
 			return EDEADLK;
 #if defined(__EMSCRIPTEN__) && !defined(NDEBUG)
 		// Extra check for deadlock in debug builds, but only if we would block
 		// forever (at == NULL).
-		assert(at || own != __pthread_self()->tid && "pthread mutex deadlock detected");
+		assert(at || own != CURRENT_THREAD_ID && "pthread mutex deadlock detected");
 #endif
 
 		a_inc(&m->_m_waiters);

system/lib/libc/musl/src/thread/pthread_rwlock_timedwrlock.c

@@ -5,7 +5,7 @@ int __pthread_rwlock_timedwrlock(pthread_rwlock_t *restrict rw, const struct tim
 #ifdef __EMSCRIPTEN__
 	/// XXX Emscripten: The spec allows detecting when multiple write locks would deadlock, which we do here to avoid hangs.
 	/// If attempting to lock the write lock that we already own, error out.
-	if (rw->_rw_wr_owner == __pthread_self()->tid) return EDEADLK;
+	if (rw->_rw_wr_owner == CURRENT_THREAD_ID) return EDEADLK;
 #endif
 	int r, t;
 
@@ -27,7 +27,7 @@ int __pthread_rwlock_timedwrlock(pthread_rwlock_t *restrict rw, const struct tim
 #ifdef __EMSCRIPTEN__
 	/// XXX Emscripten: The spec allows detecting when multiple write locks would deadlock, which we do here to avoid hangs.
 	/// Mark this thread as the owner of this write lock.
-	rw->_rw_wr_owner = __pthread_self()->tid;
+	rw->_rw_wr_owner = CURRENT_THREAD_ID;
 #endif
 	return r;
 }

system/lib/libc/musl/src/thread/pthread_rwlock_trywrlock.c

@@ -6,7 +6,7 @@ int __pthread_rwlock_trywrlock(pthread_rwlock_t *rw)
 #ifdef __EMSCRIPTEN__
 	/// XXX Emscripten: The spec allows detecting when multiple write locks would deadlock, which we do here to avoid hangs.
 	/// Mark this thread to own the write lock, to ignore multiple attempts to lock.
-	rw->_rw_wr_owner = __pthread_self()->tid;
+	rw->_rw_wr_owner = CURRENT_THREAD_ID;
 #endif
 	return 0;
 }

system/lib/libc/musl/src/thread/pthread_rwlock_unlock.c

@@ -7,7 +7,7 @@ int __pthread_rwlock_unlock(pthread_rwlock_t *rw)
 #ifdef __EMSCRIPTEN__
 	/// XXX Emscripten: The spec allows detecting when multiple write locks would deadlock, which we do here to avoid hangs.
 	/// Mark this thread to not own the write lock anymore.
-	if (rw->_rw_wr_owner == __pthread_self()->tid) rw->_rw_wr_owner = 0;
+	if (rw->_rw_wr_owner == CURRENT_THREAD_ID) rw->_rw_wr_owner = 0;
 #endif
 
 	do {

system/lib/libcxxabi/src/cxa_guard_impl.h

@@ -64,11 +64,6 @@
 #include <limits.h>
 #include <stdlib.h>
 
-#ifdef __EMSCRIPTEN__
-#include <emscripten/threading.h>
-#include <math.h>
-#endif
-
 #ifndef _LIBCXXABI_HAS_NO_THREADS
 #  if defined(__ELF__) && defined(_LIBCXXABI_LINK_PTHREAD_LIB)
 #    pragma comment(lib, "pthread")
@@ -430,13 +425,6 @@ void PlatformFutexWake(int* addr) {
   __tsan_release(addr);
   futex(reinterpret_cast<volatile uint32_t*>(addr), WAKE, INT_MAX, NULL, NULL);
 }
-#elif defined(__EMSCRIPTEN__)
-void PlatformFutexWait(int* addr, int expect) {
-  emscripten_futex_wait(addr, expect, INFINITY);
-}
-void PlatformFutexWake(int* addr) {
-  emscripten_futex_wake(addr, INT_MAX);
-}
 #elif defined(SYS_futex)
 void PlatformFutexWait(int* addr, int expect) {
   constexpr int WAIT = 0;

test/codesize/test_codesize_minimal_pthreads_memgrowth.json

@@ -2,9 +2,9 @@
   "a.out.js": 7766,
   "a.out.js.gz": 3812,
   "a.out.nodebug.wasm": 19266,
-  "a.out.nodebug.wasm.gz": 8935,
+  "a.out.nodebug.wasm.gz": 8934,
   "total": 27032,
-  "total_gz": 12747,
+  "total_gz": 12746,
   "sent": [
     "a (memory)",
     "b (emscripten_get_now)",

test/test_other.py

@@ -13513,7 +13513,7 @@ def test_wasm_worker_preprocessor_flags(self):
 
   @also_with_minimal_runtime
   def test_wasm_worker_pthread_api_usage(self):
-    self.assert_fail([EMCC, test_file('wasm_worker/wasm_worker_pthread_api_usage.c'), '-sWASM_WORKERS'], 'undefined symbol: pthread_mutex_lock')
+    self.do_runf('wasm_worker/wasm_worker_pthread_api_usage.c', cflags=['-sWASM_WORKERS'])
 
   @also_with_minimal_runtime
   def test_wasm_worker_cxx_init(self):

tools/system_libs.py

@@ -1188,19 +1188,6 @@ def get_files(self):
 
     ignore += LIBC_SOCKETS
     if self.is_mt:
-      ignore += [
-        'clone.c',
-        'pthread_create.c',
-        'pthread_kill.c', 'pthread_sigmask.c',
-        '__set_thread_area.c', 'synccall.c',
-        '__syscall_cp.c', '__tls_get_addr.c',
-        '__unmapself.c',
-        # Empty files, simply ignore them.
-        'syscall_cp.c', 'tls.c',
-        # TODO: Support these. See #12216.
-        'pthread_setname_np.c',
-        'pthread_getname_np.c',
-      ]
       libc_files += files_in_path(
         path='system/lib/pthread',
         filenames=[
@@ -1215,80 +1202,89 @@ def get_files(self):
           'emscripten_yield.c',
           'thread_profiler.c',
         ])
+    elif self.is_ww:
+      ignore += ['pthread_self.c']
+      libc_files += files_in_path(
+        path='system/lib/libc',
+        filenames=['emscripten_yield_stub.c'])
     else:
       ignore += ['thread']
       libc_files += files_in_path(
         path='system/lib/libc',
         filenames=['emscripten_yield_stub.c'])
 
-      if self.is_ww:
-        libc_files += files_in_path(
-          path='system/lib/libc/musl/src/thread',
-          filenames=[
-            '__lock.c',
-            '__wait.c',
-            'lock_ptc.c',
-          ])
-      else:
-        # Include stub version of thread functions when building
-        # in single theaded mode.
-        # Note: We do *not* include these stubs in the Wasm Workers build since it would
-        # never be safe to call these from a Wasm Worker.
-        libc_files += files_in_path(
-          path='system/lib/pthread',
-          filenames=[
-            'library_pthread_stub.c',
-            'pthread_self_stub.c',
-            'proxying_stub.c',
-          ])
-        libc_files += files_in_path(
-          path='system/lib/libc/musl/src/thread',
-          filenames=[
-            'pthread_self.c',
-            'pthread_cleanup_push.c',
-            'pthread_attr_init.c',
-            'pthread_attr_destroy.c',
-            'pthread_attr_get.c',
-            'pthread_attr_setdetachstate.c',
-            'pthread_attr_setguardsize.c',
-            'pthread_attr_setinheritsched.c',
-            'pthread_attr_setschedparam.c',
-            'pthread_attr_setschedpolicy.c',
-            'pthread_attr_setscope.c',
-            'pthread_attr_setstack.c',
-            'pthread_attr_setstacksize.c',
-            'pthread_getattr_np.c',
-            'pthread_getconcurrency.c',
-            'pthread_getcpuclockid.c',
-            'pthread_getschedparam.c',
-            'pthread_setschedprio.c',
-            'pthread_setconcurrency.c',
-            'default_attr.c',
-            # C11 thread library functions
-            'call_once.c',
-            'tss_create.c',
-            'tss_delete.c',
-            'tss_set.c',
-            'cnd_broadcast.c',
-            'cnd_destroy.c',
-            'cnd_init.c',
-            'cnd_signal.c',
-            'cnd_timedwait.c',
-            'cnd_wait.c',
-            'mtx_destroy.c',
-            'mtx_init.c',
-            'mtx_lock.c',
-            'mtx_timedlock.c',
-            'mtx_trylock.c',
-            'mtx_unlock.c',
-            'thrd_create.c',
-            'thrd_exit.c',
-            'thrd_join.c',
-            'thrd_sleep.c',
-            'thrd_yield.c',
-          ])
+      # Include stub version of thread functions when building
+      # in single theaded mode.
+      # Note: We do *not* include these stubs in the Wasm Workers build since it would
+      # never be safe to call these from a Wasm Worker.
+      libc_files += files_in_path(
+        path='system/lib/pthread',
+        filenames=[
+          'library_pthread_stub.c',
+          'pthread_self_stub.c',
+          'proxying_stub.c',
+        ])
+      libc_files += files_in_path(
+        path='system/lib/libc/musl/src/thread',
+        filenames=[
+          'pthread_self.c',
+          'pthread_cleanup_push.c',
+          'pthread_attr_init.c',
+          'pthread_attr_destroy.c',
+          'pthread_attr_get.c',
+          'pthread_attr_setdetachstate.c',
+          'pthread_attr_setguardsize.c',
+          'pthread_attr_setinheritsched.c',
+          'pthread_attr_setschedparam.c',
+          'pthread_attr_setschedpolicy.c',
+          'pthread_attr_setscope.c',
+          'pthread_attr_setstack.c',
+          'pthread_attr_setstacksize.c',
+          'pthread_getattr_np.c',
+          'pthread_getconcurrency.c',
+          'pthread_getcpuclockid.c',
+          'pthread_getschedparam.c',
+          'pthread_setschedprio.c',
+          'pthread_setconcurrency.c',
+          'default_attr.c',
+          # C11 thread library functions
+          'call_once.c',
+          'tss_create.c',
+          'tss_delete.c',
+          'tss_set.c',
+          'cnd_broadcast.c',
+          'cnd_destroy.c',
+          'cnd_init.c',
+          'cnd_signal.c',
+          'cnd_timedwait.c',
+          'cnd_wait.c',
+          'mtx_destroy.c',
+          'mtx_init.c',
+          'mtx_lock.c',
+          'mtx_timedlock.c',
+          'mtx_trylock.c',
+          'mtx_unlock.c',
+          'thrd_create.c',
+          'thrd_exit.c',
+          'thrd_join.c',
+          'thrd_sleep.c',
+          'thrd_yield.c',
+        ])
 
     if self.is_mt or self.is_ww:
+      ignore += [
+        'clone.c',
+        'pthread_create.c',
+        'pthread_kill.c', 'pthread_sigmask.c',
+        '__set_thread_area.c', 'synccall.c',
+        '__syscall_cp.c', '__tls_get_addr.c',
+        '__unmapself.c',
+        # Empty files, simply ignore them.
+        'syscall_cp.c', 'tls.c',
+        # TODO: Support these. See #12216.
+        'pthread_setname_np.c',
+        'pthread_getname_np.c',
+      ]
       # Low level thread primitives available in both pthreads and wasm workers builds.
       libc_files += files_in_path(
         path='system/lib/pthread',
@@ -1303,6 +1299,7 @@ def get_files(self):
     ignore += ['pow_small.c', 'log_small.c', 'log2_small.c']
 
     ignore = set(ignore)
+    print(ignore)
     for dirpath, dirnames, filenames in os.walk(musl_srcdir):
       # Don't recurse into ignored directories
       remove = [d for d in dirnames if d in ignore]
@@ -1616,7 +1613,6 @@ class libcxxabi(ExceptionLibrary, MTLibrary, DebugLibrary):
   name = 'libc++abi'
   cflags = [
       '-Oz',
-      '-D_LIBCXXABI_USE_FUTEX',
       '-D_LIBCPP_BUILDING_LIBRARY',
       '-D_LIBCXXABI_BUILDING_LIBRARY',
       '-DLIBCXXABI_NON_DEMANGLING_TERMINATE',