lost of SIGIO in SunOS4.1/4.0.3

[THE AGEIS]

Hi netlander,
        I am writing some network applications using socket & shared memory.
I used SIGIO to notify the receiver when there is data available in the
shared memory. SIGIO is needed here coz the receiver is polling the socket
using select(2). So I need SIGIO to purposely interrupt the select(2) call.
        This SIGIO signal is sent by the sender using kill(2). However, I
found out SOME (not ALL - the last few sent) SIGIO signals are lost.
I thought SunOS4.1 provides reliable signal as described by Steven in his
Unix network Programming book. Is it true? At last, I suspected the signals
are lost probably because the sender was sending too many signals
too fast. As a result, I purposely slowed down the receiver using sleep(2).
The result turned out to be NO signal was lost. Could somebody please shed
some light on me whether SunOS4.1/4.0.3 DOES deliver the signal reliably?
Or did I missed sth? Anybody has the similar experience?
        Thanks a lot.

- Beng Hang (email: taybengh at nusdiscs.bitnet)
  Dept. Of Info. Syst. and Comp. Sc.
  National University of Singapore