On 05/29/2013 09:04 AM, John Reiser wrote: > Comment: In practice SIGRTMIN is a very stable value. For each architecture > SIGRTMIN is chosen at the time of the original port, and after that SIGRTMIN > "never" will change, although in theory it could. The value of SIGRTMAX > is less stable because it changes whenever _NSIG changes. _NSIG has changed > from 32 to 64, and in some cases has reverted to 32 in order to save 4 bytes > [or 4*sizeof(void *)] in various places, and to make code smaller and simpler > [because (32/8)==sizeof(unsigned int)].
_NSIG == 32 is only possible on platforms that are not aiming for POSIX compliance; POSIX requires enough signals, including a minimum of 8 realtime signals, that you pretty much need _NSIG == 64 to comply with POSIX. That said, cygwin is a platform that has not (yet) converted to _NSIG == 64, and currently cheats by providing SIGRTMIN == SIGRTMAX for only 1 realtime signal. I agree that SIGRTMIN is unlikely to change for a given platform, except in the rare case of an API change from 32 to 64 (requiring a recompile of pretty much everything on that platform to take advantage of the new API, while still providing ABI compatibility for older applications to continue to run even without recompilation). -- Eric Blake eblake redhat com +1-919-301-3266 Libvirt virtualization library http://libvirt.org
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