Initial project import

tools/v/vlib/os/execute_lock_nix.c.v

@@ -0,0 +1,27 @@
+@[has_globals]
+module os
+
+// g_v_os_execute_mutex_storage backs a pthread_mutex_t used to serialize
+// pipe()+spawn from os.execute(). On macOS arm64 GitHub Actions runners,
+// two threads racing through pipe()+posix_spawn produced empty captured
+// output even with FD_CLOEXEC on the pipe ends. 128 bytes is comfortably
+// larger than sizeof(pthread_mutex_t) on macOS (64) and Linux (40-48),
+// so we never need to know the actual layout — only the C functions
+// declared in builtin/cfns.c.v which take voidptr.
+__global g_v_os_execute_mutex_storage = [128]u8{}
+
+fn v_os_execute_mutex_ptr() voidptr {
+	return unsafe { voidptr(&g_v_os_execute_mutex_storage[0]) }
+}
+
+fn init() {
+	C.pthread_mutex_init(v_os_execute_mutex_ptr(), unsafe { nil })
+}
+
+fn v_os_execute_lock() {
+	C.pthread_mutex_lock(v_os_execute_mutex_ptr())
+}
+
+fn v_os_execute_unlock() {
+	C.pthread_mutex_unlock(v_os_execute_mutex_ptr())
+}