Fast sigblock (AKA rtld speedup)

[Konstantin Belousov]

On Sun, Jan 13, 2013 at 02:32:00PM +0100, Jilles Tjoelker wrote:
> On Sat, Jan 12, 2013 at 05:25:47PM +0100, Jilles Tjoelker wrote:
> > This suggests a different rather simpler change. Libthr can always use
> > its rtld lock implementation instead of only when multiple threads
> > exist. This avoids the sigprocmask() syscalls and should not be much
> > slower than the default implementation in rtld because that also
> > contains atomic operations (both the unpatched and the patched version).
> > People that care about performance of exceptions can then link in libthr
> > (in many cases, it is already linked in to allow for (the possibility
> > of) threading).
> 
> > I have tested this and exceptions were indeed more than twice as fast in
> > my test program if I created an extra thread doing nothing than in the
> > fully single-threaded version (with or without libthr).
> 
> Here is a patch. It is lightly tested.
> 
> The function _thr_rtld_fini() can be removed afterwards because it is no
> longer used.
> 
> Index: lib/libthr/thread/thr_init.c
> ===================================================================
> --- lib/libthr/thread/thr_init.c	(revision 244639)
> +++ lib/libthr/thread/thr_init.c	(working copy)
> @@ -363,6 +363,7 @@
>  		_thr_signal_init();
>  		if (_thread_event_mask & TD_CREATE)
>  			_thr_report_creation(curthread, curthread);
> +		_thr_rtld_init();
Please add a comment there, describing the reason for initializing
threaded rtld locks.

>  	}
>  }
>  
> Index: lib/libthr/thread/thr_kern.c
> ===================================================================
> --- lib/libthr/thread/thr_kern.c	(revision 244639)
> +++ lib/libthr/thread/thr_kern.c	(working copy)
> @@ -57,11 +57,6 @@
>  		return (0);
>  
>  	__isthreaded = threaded;
> -	if (threaded != 0) {
> -		_thr_rtld_init();
> -	} else {
> -		_thr_rtld_fini();
> -	}
>  	return (0);
>  }

I do not object.
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