On Thu, Jul 25, 2019 at 01:43:59PM +0200, Oleg Nesterov wrote: > Or. We can change wait_consider_task() to not clear ->notask_error if > WXXX and the child is PF_WAIT_PID. > > This way you can "safely" use wait() without WNOHANG, it won't block if > all the children which can report an even are PF_WAIT_PID. > > But I do not understand your use-cases, I have no idea if this can help One usecase (among others listed in the commit message) are shared libraries. P_ALL is usually something you can't really use in a shared library because you have no idea what else might be fork()ed off. Only the main program can use this but none of the auxiliary libraries that it uses. The other way around you want to be able fork() off something without affecting P_ALL in the main program. The key is that you want to be able to create child processes in a shared library without the main programing having to know about this so that it can use P_ALL and never get stuff from the library. Assume you have a project with a main loop with a million things happening in that mainloop like some gui app running an avi video. For example, gtk uses gstreamer which forks off all codecs in child processes which are sandboxed for security. So gstreamer is using helper processes in the background which are my children now. Now I'm creating four more additional helper processes as well. Now, in my (glib, qt whatever) mainloop on SIGCHLD some part of the app is checking with WNHOANG and finds a process has exited. It's cleaning this thing up now but it's not a process it wanted to clean up. The other part of the app is now doing waitid(P_PID, pid) but will find the process already gone it wanted to reap. I hope I'm expressing this well enough.
