threads: enable access to pthread_barrier_* functions (#358)

In building some `libc-test` tests, I found these functions were not
compiled in. This change adds `pthread_barrier_init`,
`pthread_barrier_wait`, and `pthread_barrier_destroy` to the
`THREAD_MODEL=posix` build. As has been done with previous pthreads PRs,
this PR skips any inter-process locking by removing any calls to
`__vm_lock` and friends. If in the future WASI gains the "process"
concept, then these locations (and the pre-existing ones) will need to
be modified.

Author: abrown

Makefile

@@ -204,6 +204,9 @@ LIBC_TOP_HALF_MUSL_SOURCES += \
         thread/pthread_attr_init.c \
         thread/pthread_attr_setstack.c \
         thread/pthread_attr_setstacksize.c \
+        thread/pthread_barrier_destroy.c \
+        thread/pthread_barrier_init.c \
+        thread/pthread_barrier_wait.c \
         thread/pthread_cleanup_push.c \
         thread/pthread_cond_broadcast.c \
         thread/pthread_cond_destroy.c \

expected/wasm32-wasi/posix/defined-symbols.txt

@@ -981,6 +981,9 @@ pthread_attr_getstacksize
 pthread_attr_init
 pthread_attr_setstack
 pthread_attr_setstacksize
+pthread_barrier_destroy
+pthread_barrier_init
+pthread_barrier_wait
 pthread_barrierattr_getpshared
 pthread_cond_broadcast
 pthread_cond_destroy

libc-top-half/musl/src/thread/pthread_barrier_destroy.c

@@ -9,7 +9,9 @@ int pthread_barrier_destroy(pthread_barrier_t *b)
 			while ((v = b->_b_lock) & INT_MAX)
 				__wait(&b->_b_lock, 0, v, 0);
 		}
+#ifdef __wasilibc_unmodified_upstream /* WASI does not understand processes or locking between them. */
 		__vm_wait();
+#endif
 	}
 	return 0;
 }

libc-top-half/musl/src/thread/pthread_barrier_wait.c

@@ -23,7 +23,9 @@ static int pshared_barrier_wait(pthread_barrier_t *b)
 			__wait(&b->_b_count, &b->_b_waiters2, v, 0);
 	}
 
+#ifdef __wasilibc_unmodified_upstream /* WASI does not understand processes or locking between them. */
 	__vm_lock();
+#endif
 
 	/* Ensure all threads have a vm lock before proceeding */
 	if (a_fetch_add(&b->_b_count, -1)==1-limit) {
@@ -44,7 +46,9 @@ static int pshared_barrier_wait(pthread_barrier_t *b)
 	if (v==INT_MIN+1 || (v==1 && w))
 		__wake(&b->_b_lock, 1, 0);
 
+#ifdef __wasilibc_unmodified_upstream /* WASI does not understand processes or locking between them. */
 	__vm_unlock();
+#endif
 
 	return ret;
 }
@@ -84,8 +88,12 @@ int pthread_barrier_wait(pthread_barrier_t *b)
 			a_spin();
 		a_inc(&inst->finished);
 		while (inst->finished == 1)
+#ifdef __wasilibc_unmodified_upstream
 			__syscall(SYS_futex,&inst->finished,FUTEX_WAIT|FUTEX_PRIVATE,1,0) != -ENOSYS
 			|| __syscall(SYS_futex,&inst->finished,FUTEX_WAIT,1,0);
+#else
+			__futexwait(&inst->finished, 1, 0);
+#endif
 		return PTHREAD_BARRIER_SERIAL_THREAD;
 	}