I found an answer on this https://www.qnx.com/developers/docs/6.5.0SP1.update/com.qnx.doc.neutrino_lib_ref/s/spawnv.html site, where it says

P_NOWAIT — execute the parent program concurrently with the new child process.
P_NOWAITO — execute the parent program concurrently with the new child process. You can't use wait() to obtain the exit code. 

but i'm not sure if this applies to windows (cause it doesn't have wait(), only WaitForSingleObject()) and if by using P_NOWAIT I am obliged to call wait() on the pid