#include <x/signalfd.H> x::signalfd fd=x::signalfd::create(); fd->capture(SIGHUP); fd->nonblock(true); // ... x::signalfd::getsignal_t gs=fd->getsignal(); if (gs.ssi_signo == SIGHUP) handle_sighup();
This is an implementation of signal file descriptors, a Linux kernel specific feature. A signal file descriptor enables the implementation of signal processing by reading a file descriptor in an orderly fashion, instead of installing an asynchronous signal handler, and being constrained by the reentrance requirements imposed on asynchronous signal handlers.
A x::signalfd
is a file descriptor.
The list of signals processed via the signal file descriptor must be
explicitly declared by invoking
capture() (and undone by
uncapture(), if needed).
Upon receipt of a signal, instead of interrupting the process and
invoking a signal handler, the signal file descriptor becomes readable
(and for that reason it's usually made non-blocking).
Reading from the underlying file descriptor returns a structure.
This implementation provides a convenient wrapper,
getsignal() that gives the structure read from the
signal file descriptor. Of particular importance, its
ssi_signo gives the signal number received by the
process. The same signal file descriptor can capture multiple signals.
If no signals are pending for the process,
getsignal() blocks until a capture signal gets
delivered, if the signal file descriptor is blocking.
getsignal() returns immediately for a non-blocking
file descriptor, with the signal number given as 0.
As noted by
signalfd(2), signals must be blocked before they can be captured
by a file descriptor, and any execution thread that does not have
the signal blocked will catch the signal instead of it being reported
via a signal file descriptor. Applications that use signal file
descriptors should block them in main(), before
starting any threads.