Programming

It looks to me like your code should work. What version of Unix are you using? Have you searched for any kernel patches that might fix your kernel?

I do continue to have reservations about your use of sigqueue. Should your kernel start to work correctly, your program should then correctly start to document the loss of signals. You need to check for the queue being full. By putting printf's and fflush's in you signal handler you are greatly exacerbating any problems the parent will have in processing signals fast enough.

I putted printf & fflush statements for debugging purposes.The problem still exists without these statements..

I have a Linux 2.4.31 kernel, I'm using SlackWare 10.2 over VMware Workstation 5.5.I also have a telnet & ftp access to a SUSE LINUX Enterprise Server 9 (x86_64) - Kernel 2.6.5-7.276-smp.Problems are the same...

While experimenting I found that by simply using kill, fewer signals are lost.

Just for the heck of it, I would try SIGRTMIN rather than SIGUSR1, which should be easy to try. If it is failing on a 2.6 kernel with smp support, there is not much point in trying another kernel. Although there is a product called RTLinux which claims complete Posix Realtime compliance link.

Well here is something unexpected :

SIGRTMIN worked on the Linux 2.4.31 kernel of SlackWare 10.2
but
failed on the SUSE LINUX Enterprise Server 9 (x86_64) - Kernel 2.6.5-7.276-smp.

Well, SuSE is actually a supported product. Maybe you can ask Novell for a patch.

Thank you for your help.

I'm finaly droping signals.I have a solution using sockets that works with no problems on different machines.