Re: cvs commit: src/sys/conf files src/sys/kern init_main.c kern_acct.c kern_exit.c kern_fork.c kern_plimit.c kern_resource.c kern_synch.c syscalls.master src/sys/sys kern_syscall.h proc.h resourcevar.h

[David Xu <davidxu@xxxxxxxxxxx>]

Matthew Dillon wrote:
>     All the LWPs share one limits structure (since the limits structure
>     is embedded in the process, not the lwp).   But this limits structure
>     might have been inherited from other unrelated processes when the
>     threaded program was fork/execed.
>
>     When a process tries to create a second LWP (in the future, when that
>     function is supported), the limits structure needs to be disconnected
>     from those other unrelated processes so the threaded process has sole
>     ownership of it.
>
>     If we don't do this, then any LWP trying to modify a resource limit
>     would have to perform the copy-on-write to replace the process's
>     p_limits structure in the face of other LWPs potentially also accessing
>     proc->p_limits.  We would have to obtain a spinlock on the process
>     AND the limits structure to prevent a race.
>
>     But if when a process tries to rfork a second thread we unshare the
>     limits structure from other unrelated processes, now proc->p_limits
>     is set in stone and all LWP threads will only have to spinlock
>     the limits structure (and not have to spinlock the proc structure to
>     get to the limits structure).
>
>     So that rule greatly reduces code complexity.
>
> 					-Matt
> 					Matthew Dillon 
> 					<dillon@xxxxxxxxxxxxx>
Thanks, I misunderstood your commit log.

David Xu