emscripten-core · sbc100 · Apr 22, 2026 · Apr 21, 2026
diff --git a/ChangeLog.md b/ChangeLog.md
@@ -36,6 +36,8 @@ See docs/process.md for more on how version tagging works.
   explicitly allow for returning EINTR when the wait is interrupted by an async
   operation.  All callers of emscripten_futux_wait are advised to use a loop
   to handle these types of spurious wakeups / interruptions. (#26659, #26735)
+- Attempting to use PTHREAD_PROCESS_SHARED when creating pthread primitives such
+  as locks and condvars will now fail with ENOTSUP. (#26743)
 
 5.0.6 - 04/14/26
 ----------------

diff --git a/system/lib/libc/musl/include/unistd.h b/system/lib/libc/musl/include/unistd.h
@@ -263,7 +263,11 @@ pid_t gettid(void);
 #else
 #define _POSIX_THREADS          _POSIX_VERSION
 #endif
+#ifndef __EMSCRIPTEN__
 #define _POSIX_THREAD_PROCESS_SHARED _POSIX_VERSION
+#else
+#define _POSIX_THREAD_PROCESS_SHARED -1
+#endif
 #define _POSIX_THREAD_SAFE_FUNCTIONS _POSIX_VERSION
 #define _POSIX_THREAD_ATTR_STACKADDR _POSIX_VERSION
 #define _POSIX_THREAD_ATTR_STACKSIZE _POSIX_VERSION

diff --git a/system/lib/libc/musl/src/thread/pthread_condattr_setpshared.c b/system/lib/libc/musl/src/thread/pthread_condattr_setpshared.c
@@ -3,6 +3,9 @@
 int pthread_condattr_setpshared(pthread_condattr_t *a, int pshared)
 {
 	if (pshared > 1U) return EINVAL;
+#ifdef __EMSCRIPTEN__
+	if (pshared) return ENOTSUP;
+#endif
 	a->__attr &= 0x7fffffff;
 	a->__attr |= (unsigned)pshared<<31;
 	return 0;

diff --git a/system/lib/libc/musl/src/thread/pthread_mutexattr_setpshared.c b/system/lib/libc/musl/src/thread/pthread_mutexattr_setpshared.c
@@ -3,6 +3,9 @@
 int pthread_mutexattr_setpshared(pthread_mutexattr_t *a, int pshared)
 {
 	if (pshared > 1U) return EINVAL;
+#ifdef __EMSCRIPTEN__
+	if (pshared) return ENOTSUP;
+#endif
 	a->__attr &= ~128U;
 	a->__attr |= pshared<<7;
 	return 0;

diff --git a/system/lib/libc/musl/src/thread/pthread_rwlockattr_setpshared.c b/system/lib/libc/musl/src/thread/pthread_rwlockattr_setpshared.c
@@ -3,6 +3,9 @@
 int pthread_rwlockattr_setpshared(pthread_rwlockattr_t *a, int pshared)
 {
 	if (pshared > 1U) return EINVAL;
+#ifdef __EMSCRIPTEN__
+	if (pshared) return ENOTSUP;
+#endif
 	a->__attr[0] = pshared;
 	return 0;
 }
diff --git a/system/lib/libc/musl/src/thread/sem_init.c b/system/lib/libc/musl/src/thread/sem_init.c
@@ -8,6 +8,9 @@ int sem_init(sem_t *sem, int pshared, unsigned value)
 		errno = EINVAL;
 		return -1;
 	}
+#ifdef __EMSCRIPTEN__
+	if (pshared) return ENOTSUP;
+#endif
 	sem->__val[0] = value;
 	sem->__val[1] = 0;
 	sem->__val[2] = pshared ? 0 : 128;

diff --git a/system/lib/pthread/library_pthread_stub.c b/system/lib/pthread/library_pthread_stub.c
@@ -268,43 +268,6 @@ int pthread_kill(pthread_t thread, int sig) {
   return 0;
 }
 
-int pthread_mutexattr_init(pthread_mutexattr_t *attr) {
-  return 0;
-}
-
-int pthread_mutexattr_setprotocol(pthread_mutexattr_t *attr, int protocol) {
-  return 0;
-}
-
-int pthread_mutexattr_settype(pthread_mutexattr_t *attr, int type) {
-  return 0;
-}
-
-int pthread_mutexattr_destroy(pthread_mutexattr_t *attr) {
-  return 0;
-}
-
-int pthread_mutexattr_setpshared(pthread_mutexattr_t *attr, int pshared) {
-  // XXX implement if/when getpshared is required
-  return 0;
-}
-
-int pthread_condattr_init(pthread_condattr_t * attr) {
-  return 0;
-}
-
-int pthread_condattr_destroy(pthread_condattr_t *attr) {
-  return 0;
-}
-
-int pthread_condattr_setclock(pthread_condattr_t *attr, clockid_t clk) {
-  return 0;
-}
-
-int pthread_condattr_setpshared(pthread_condattr_t *attr, int shared) {
-  return 0;
-}
-
 int pthread_setcancelstate(int state, int* oldstate) {
   return 0;
 }
@@ -349,42 +312,6 @@ int pthread_rwlock_unlock(pthread_rwlock_t *rwlock) {
   return 0;
 }
 
-int pthread_rwlockattr_init(pthread_rwlockattr_t *attr) {
-  return 0;
-}
-
-int pthread_rwlockattr_destroy(pthread_rwlockattr_t *attr) {
-  return 0;
-}
-
-int pthread_rwlockattr_setpshared(pthread_rwlockattr_t* attr, int pshared) {
-  return 0;
-}
-
-int pthread_spin_init(pthread_spinlock_t *lock, int pshared) {
-  return 0;
-}
-
-int pthread_spin_destroy(pthread_spinlock_t *lock) {
-  return 0;
-}
-
-int pthread_spin_lock(pthread_spinlock_t *lock) {
-  return 0;
-}
-
-int pthread_spin_trylock(pthread_spinlock_t *lock) {
-  return 0;
-}
-
-int pthread_spin_unlock(pthread_spinlock_t *lock) {
-  return 0;
-}
-
-int sem_init(sem_t *sem, int pshared, unsigned int value) {
-  return 0;
-}
-
 int sem_post(sem_t *sem) {
   return 0;
 }
@@ -397,10 +324,6 @@ int sem_trywait(sem_t *sem) {
   return 0;
 }
 
-int sem_destroy(sem_t *sem) {
-  return 0;
-}
-
 // When pthreads is not enabled, we can't use the Atomics futex api to do
 // proper sleeps, so simulate a busy spin wait loop instead.
 void emscripten_thread_sleep(double msecs) {

diff --git a/test/codesize/test_codesize_cxx_wasmfs.json b/test/codesize/test_codesize_cxx_wasmfs.json
@@ -1,10 +1,10 @@
 {
   "a.out.js": 7023,
   "a.out.js.gz": 3310,
-  "a.out.nodebug.wasm": 172710,
-  "a.out.nodebug.wasm.gz": 63307,
-  "total": 179733,
-  "total_gz": 66617,
+  "a.out.nodebug.wasm": 172741,
+  "a.out.nodebug.wasm.gz": 63318,
+  "total": 179764,
+  "total_gz": 66628,
   "sent": [
     "__cxa_throw",
     "_abort_js",

diff --git a/test/codesize/test_codesize_files_wasmfs.json b/test/codesize/test_codesize_files_wasmfs.json
@@ -1,10 +1,10 @@
 {
   "a.out.js": 5465,
   "a.out.js.gz": 2575,
-  "a.out.nodebug.wasm": 58418,
-  "a.out.nodebug.wasm.gz": 18067,
-  "total": 63883,
-  "total_gz": 20642,
+  "a.out.nodebug.wasm": 58426,
+  "a.out.nodebug.wasm.gz": 18182,
+  "total": 63891,
+  "total_gz": 20757,
   "sent": [
     "a (emscripten_date_now)",
     "b (emscripten_err)",
@@ -113,6 +113,7 @@
     "$std::__2::basic_string<char\\2c\\20std::__2::char_traits<char>\\2c\\20std::__2::allocator<char>>&\\20std::__2::basic_string<char\\2c\\20std::__2::char_traits<char>\\2c\\20std::__2::allocator<char>>::__assign_no_alias<true>\\28char\\20const*\\2c\\20unsigned\\20long\\29",
     "$std::__2::basic_string<char\\2c\\20std::__2::char_traits<char>\\2c\\20std::__2::allocator<char>>::__grow_by_and_replace\\28unsigned\\20long\\2c\\20unsigned\\20long\\2c\\20unsigned\\20long\\2c\\20unsigned\\20long\\2c\\20unsigned\\20long\\2c\\20unsigned\\20long\\2c\\20char\\20const*\\29",
     "$std::__2::basic_string<char\\2c\\20std::__2::char_traits<char>\\2c\\20std::__2::allocator<char>>::__init_copy_ctor_external\\28char\\20const*\\2c\\20unsigned\\20long\\29",
+    "$std::__2::recursive_mutex::recursive_mutex\\28\\29",
     "$std::__2::shared_ptr<wasmfs::SpecialFiles::\\28anonymous\\20namespace\\29::RandomFile>\\20std::__2::make_shared\\5babi:nn210108\\5d<wasmfs::SpecialFiles::\\28anonymous\\20namespace\\29::RandomFile\\2c\\200>\\28\\29",
     "$std::__2::vector<unsigned\\20char\\2c\\20std::__2::allocator<unsigned\\20char>>::__append\\28unsigned\\20long\\29",
     "$std::__2::vector<wasmfs::MemoryDirectory::ChildEntry\\2c\\20std::__2::allocator<wasmfs::MemoryDirectory::ChildEntry>>::erase\\5babi:nn210108\\5d\\28std::__2::__wrap_iter<wasmfs::MemoryDirectory::ChildEntry\\20const*>\\29",

diff --git a/test/codesize/test_codesize_hello_dylink_all.json b/test/codesize/test_codesize_hello_dylink_all.json
@@ -1,7 +1,7 @@
 {
   "a.out.js": 244416,
-  "a.out.nodebug.wasm": 577672,
-  "total": 822088,
+  "a.out.nodebug.wasm": 578085,
+  "total": 822501,
   "sent": [
     "IMG_Init",
     "IMG_Load",
@@ -4620,6 +4620,9 @@
     "$pthread_barrierattr_getpshared",
     "$pthread_condattr_getclock",
     "$pthread_condattr_getpshared",
+    "$pthread_condattr_init",
+    "$pthread_condattr_setclock",
+    "$pthread_condattr_setpshared",
     "$pthread_equal",
     "$pthread_getattr_np",
     "$pthread_getcpuclockid",
@@ -4629,8 +4632,16 @@
     "$pthread_mutexattr_getpshared",
     "$pthread_mutexattr_getrobust",
     "$pthread_mutexattr_gettype",
+    "$pthread_mutexattr_setprotocol",
+    "$pthread_mutexattr_setpshared",
+    "$pthread_mutexattr_settype",
+    "$pthread_rwlockattr_init",
+    "$pthread_rwlockattr_setpshared",
     "$pthread_setspecific",
     "$pthread_sigmask",
+    "$pthread_spin_init",
+    "$pthread_spin_lock",
+    "$pthread_spin_trylock",
     "$ptsname",
     "$putc_unlocked",
     "$putchar",
@@ -4697,6 +4708,7 @@
     "$seed48",
     "$seekdir",
     "$select",
+    "$sem_init",
     "$send",
     "$sendmmsg",
     "$sendmsg",
@@ -4736,7 +4748,6 @@
     "$sigaltstack",
     "$sigandset",
     "$sigdelset",
-    "$sigemptyset",
     "$sigfillset",
     "$siginterrupt",
     "$sigisemptyset",

diff --git a/test/test_posixtest.py b/test/test_posixtest.py
@@ -70,6 +70,13 @@ def get_tests():
 }
 
 unsupported = {
+  'test_pthread_cond_init_4_2': 'PTHREAD_PROCESS_SHARED not supported',
+  'test_pthread_condattr_getpshared_1_2': 'PTHREAD_PROCESS_SHARED not supported',
+  'test_pthread_mutexattr_setpshared_1_1': 'PTHREAD_PROCESS_SHARED not supported',
+  'test_pthread_rwlockattr_setpshared_1_1': 'PTHREAD_PROCESS_SHARED not supported',
+  'test_pthread_condattr_setpshared_1_2': 'PTHREAD_PROCESS_SHARED not supported',
+  'test_pthread_mutexattr_getpshared_1_2': 'PTHREAD_PROCESS_SHARED not supported',
+  'test_pthread_mutexattr_setpshared_2_2': 'PTHREAD_PROCESS_SHARED not supported',
   'test_pthread_exit_6_1': 'fork() and multiple processes are not supported',
   'test_pthread_atfork_1_1': 'fork() and multiple processes are not supported',
   'test_pthread_atfork_1_2': 'fork() and multiple processes are not supported',

diff --git a/tools/system_libs.py b/tools/system_libs.py
@@ -1269,10 +1269,27 @@ def get_files(self):
             'pthread_attr_setscope.c',
             'pthread_attr_setstack.c',
             'pthread_attr_setstacksize.c',
+            'pthread_condattr_destroy.c',
+            'pthread_condattr_init.c',
+            'pthread_condattr_setpshared.c',
+            'pthread_condattr_setclock.c',
+            'pthread_mutexattr_destroy.c',
+            'pthread_mutexattr_init.c',
+            'pthread_mutexattr_setprotocol.c',
+            'pthread_mutexattr_settype.c',
+            'pthread_mutexattr_setpshared.c',
+            'pthread_rwlockattr_destroy.c',
+            'pthread_rwlockattr_init.c',
+            'pthread_rwlockattr_setpshared.c',
             'pthread_getattr_np.c',
             'pthread_getconcurrency.c',
             'pthread_getcpuclockid.c',
             'pthread_getschedparam.c',
+            'pthread_spin_destroy.c',
+            'pthread_spin_init.c',
+            'pthread_spin_lock.c',
+            'pthread_spin_trylock.c',
+            'pthread_spin_unlock.c',
             'pthread_setschedprio.c',
             'pthread_setconcurrency.c',
             'default_attr.c',
@@ -1293,6 +1310,8 @@ def get_files(self):
             'mtx_timedlock.c',
             'mtx_trylock.c',
             'mtx_unlock.c',
+            'sem_destroy.c',
+            'sem_init.c',
             'thrd_create.c',
             'thrd_exit.c',
             'thrd_join.c',