Linux offers the signalfd syscall since 2.6.22 (with minor changes afterwards).  This call allows signals to be handled as bytes read out of a file descriptor, rather than as interruptions to the flow of a program.  Quite usefully, this file descriptor can be select()'d on (or poll()'d, epoll()'d, etc) alongside other "normal" file descriptors.

In order to effectively use signalfd(), the signals in question must be blocked, though.  So it makes sense to expose sigprocmask(2) at the same time, in order to allow this blocking to be set up.