Revert async cancelation behaviour to match musl

This change is partial revert of #19963.  We now match musl's behavior
which is that async cancellation does *not* work to cancel a thread
that is blocked in pthread_mutx_lock.

This reverts a few emscripten-specific patches to some very low level
parts of musl.

Author: sbc100

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

@@ -61,8 +61,8 @@ int __timedwait_cp(volatile int *addr, int val,
 	double msecsToSleep = top ? (top->tv_sec * 1000 + top->tv_nsec / 1000000.0) : INFINITY;
 
 	// cp suffix in the function name means "cancellation point", so this wait can be cancelled
-	// by the users unless current threads cancelability is set to PTHREAD_CANCEL_DISABLE
-	// which may be either done by the user of __timedwait() function.
+	// by the user, unless current thread has cancelation disabled (which may be either done
+	// directly, or indirectly, for example in the __timedwait() function).
 	pthread_t self = pthread_self();
 
 	if (self->canceldisable != PTHREAD_CANCEL_DISABLE) {
@@ -75,15 +75,14 @@ int __timedwait_cp(volatile int *addr, int val,
 				// __pthread_testcancel(), which won't return at all.
 				__pthread_testcancel();
 				// If __pthread_testcancel does return here it means that canceldisable
-				// must be set to PTHREAD_CANCEL_MASKED.  This appears to mean "return
-				// ECANCELLED to the caller".  See pthread_cond_timedwait.c for the only
-				// use of this that I could find.
+				// must be set to PTHREAD_CANCEL_MASKED.  In this case we emulate the
+				// behaviour of the futex syscall and return ECANCELLED here.
+				// See pthread_cond_timedwait.c for the only use of this flag.
 				return ECANCELED;
 			}
 			msecsToSleep = sleepUntilTime - emscripten_get_now();
 			if (msecsToSleep <= 0) {
-				r = ETIMEDOUT;
-				break;
+				return ETIMEDOUT;
 			}
 			// Must wait in slices in case this thread is cancelled in between.
 			if (msecsToSleep > max_ms_slice_to_sleep)

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

@@ -8,13 +8,7 @@ hidden long __cancel(), __syscall_cp_asm(), __syscall_cp_c();
 long __cancel()
 {
 	pthread_t self = __pthread_self();
-#ifdef __EMSCRIPTEN__
-	// Emscripten doesn't have actual async cancelation so we make a best effort
-	// by cancelling cooperatively when self->cancelasync is set.
-	if (self->canceldisable == PTHREAD_CANCEL_ENABLE || self->cancelasync)
-#else
 	if (self->canceldisable == PTHREAD_CANCEL_ENABLE)
-#endif
 		pthread_exit(PTHREAD_CANCELED);
 	self->canceldisable = PTHREAD_CANCEL_DISABLE;
 	return -ECANCELED;
@@ -83,12 +77,7 @@ static void cancel_handler(int sig, siginfo_t *si, void *ctx)
 void __testcancel()
 {
 	pthread_t self = __pthread_self();
-#ifdef __EMSCRIPTEN__
-	// See comment above about cancelasync under emscripten.
-	if (self->cancel && (self->cancelasync || !self->canceldisable))
-#else
 	if (self->cancel && !self->canceldisable)
-#endif
 		__cancel();
 }
 

system/lib/pthread/emscripten_futex_wait.c

@@ -132,7 +132,7 @@ int emscripten_futex_wait(volatile void *addr, uint32_t val, double max_wait_ms)
 
 #ifdef __EMSCRIPTEN_PTHREADS__
   pthread_t self = pthread_self();
-  bool cancelable = self->cancelasync;
+  bool cancelable = !self->canceldisable && self->cancelasync;
 #else
   bool cancelable = false;
 #endif

test/codesize/test_codesize_minimal_pthreads.json

@@ -1,10 +1,10 @@
 {
   "a.out.js": 7363,
   "a.out.js.gz": 3604,
-  "a.out.nodebug.wasm": 19239,
-  "a.out.nodebug.wasm.gz": 8916,
-  "total": 26602,
-  "total_gz": 12520,
+  "a.out.nodebug.wasm": 19244,
+  "a.out.nodebug.wasm.gz": 8919,
+  "total": 26607,
+  "total_gz": 12523,
   "sent": [
     "a (memory)",
     "b (emscripten_get_now)",

test/codesize/test_codesize_minimal_pthreads_memgrowth.json

@@ -1,10 +1,10 @@
 {
   "a.out.js": 7765,
   "a.out.js.gz": 3810,
-  "a.out.nodebug.wasm": 19240,
-  "a.out.nodebug.wasm.gz": 8917,
-  "total": 27005,
-  "total_gz": 12727,
+  "a.out.nodebug.wasm": 19245,
+  "a.out.nodebug.wasm.gz": 8920,
+  "total": 27010,
+  "total_gz": 12730,
   "sent": [
     "a (memory)",
     "b (emscripten_get_now)",

test/pthread/test_pthread_cancel_async.c

@@ -26,6 +26,7 @@ void emscripten_outf(const char* msg, ...) {
 
 pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER;
 _Atomic bool started = false;
+_Atomic bool timedlock_returned = false;
 _Atomic bool done_cleanup = false;
 
 void cleanup_handler(void *arg) {
@@ -47,12 +48,20 @@ void *thread_start(void *arg) {
   // Signal the main thread that are started
   started = true;
 
-  // This mutex is locked by the main thread so this call should never return.
-  // pthread_mutex_lock is not a cancellation point so deferred cancellation
-  // won't work here, async cancellation should.
-  pthread_mutex_lock(&mutex);
+  // At least under musl, async cancellation also does not work for
+  // pthread_mutex_lock so this call to pthread_mutex_timedlock should always
+  // timeout.
+  struct timespec ts;
+  clock_gettime(CLOCK_REALTIME, &ts);
+  ts.tv_sec += 2;
+  int rc = pthread_mutex_timedlock(&mutex, &ts);
+  timedlock_returned = true;
+  assert(rc == ETIMEDOUT);
+  emscripten_out("pthread_mutex_timedlock timed out");
+
+  pthread_testcancel();
 
-  assert(false && "pthread_mutex_lock returned!");
+  assert(false && "pthread_testcancel returned!");
   pthread_cleanup_pop(0);
 }
 
@@ -79,6 +88,7 @@ int main() {
   emscripten_out("Joining thread..");
   s = pthread_join(thr, NULL);
   assert(s == 0);
+  assert(timedlock_returned);
   emscripten_out("done");
   return 0;
 }

test/pthread/test_pthread_cancel_async.out

@@ -1,6 +1,7 @@
 Starting thread..
 Thread started!
 Canceling thread..
+pthread_mutex_timedlock timed out
 Called clean-up handler with arg 42
 Joining thread..
 done

test/test_posixtest.py

@@ -77,6 +77,7 @@ def get_tests():
   'test_pthread_join_6_3': 'creates too many threads',
   'test_pthread_barrier_wait_3_2': 'signals are not supported',
   'test_pthread_cond_broadcast_1_2': 'tries to create 10,0000 threads, then depends on fork()',
+  'test_pthread_setcanceltype_1_1': 'async cancelation does not work withing pthread_mutex_lock',
 }
 
 unsupported = {