NAME

       sd_event_add_signal, sd_event_source_get_signal, sd_event_signal_handler_t, SD_EVENT_SIGNAL_PROCMASK -
       Add a UNIX process signal event source to an event loop

SYNOPSIS

       #include <systemd/sd-event.h>

       typedef struct sd_event_source sd_event_source;

       SD_EVENT_SIGNAL_PROCMASK

       typedef int (*sd_event_signal_handler_t)(sd_event_source *s, const struct signalfd_siginfo *si,
                                                void *userdata);

       int sd_event_add_signal(sd_event *event, sd_event_source **source, int signal,
                               sd_event_signal_handler_t handler, void *userdata);

       int sd_event_source_get_signal(sd_event_source *source);

DESCRIPTION

       sd_event_add_signal() adds a new UNIX process signal event source to an event loop. The event loop object
       is specified in the event parameter, and the event source object is returned in the source parameter. The
       signal parameter specifies the numeric signal to be handled (see signal(7)).

       The handler parameter is a function to call when the signal is received or NULL. The handler function
       will be passed the userdata pointer, which may be chosen freely by the caller. The handler also receives
       a pointer to a signalfd_siginfo structure containing information about the received signal. See
       signalfd(2) for further information. The handler may return negative to signal an error (see below),
       other return values are ignored. If handler is NULL, a default handler that calls sd_event_exit(3) will
       be used.

       Only a single handler may be installed for a specific signal. The signal must be blocked in all threads
       before this function is called (using sigprocmask(2) or pthread_sigmask(3)). For convenience, if the
       special flag SD_EVENT_SIGNAL_PROCMASK is ORed into the specified signal the signal will be automatically
       masked as necessary, for the calling thread. Note that this only works reliably if the signal is already
       masked in all other threads of the process, or if there are no other threads at the moment of invocation.

       By default, the event source is enabled permanently (SD_EVENT_ON), but this may be changed with
       sd_event_source_set_enabled(3). If the handler function returns a negative error code, it will either be
       disabled after the invocation, even if the SD_EVENT_ON mode was requested before, or it will cause the
       loop to terminate, see sd_event_source_set_exit_on_failure(3).

       To destroy an event source object use sd_event_source_unref(3), but note that the event source is only
       removed from the event loop when all references to the event source are dropped. To make sure an event
       source does not fire anymore, even if it is still referenced, disable the event source using
       sd_event_source_set_enabled(3) with SD_EVENT_OFF.

       If the second parameter of sd_event_add_signal() is NULL no reference to the event source object is
       returned. In this case the event source is considered "floating", and will be destroyed implicitly when
       the event loop itself is destroyed.

       If the handler parameter to sd_event_add_signal() is NULL, and the event source fires, this will be
       considered a request to exit the event loop. In this case, the userdata parameter, cast to an integer, is
       passed as the exit code parameter to sd_event_exit(3).

       sd_event_source_get_signal() returns the configured signal number of an event source created previously
       with sd_event_add_signal(). It takes the event source object as the source parameter.

RETURN VALUE

       On success, these functions return 0 or a positive integer. On failure, they return a negative
       errno-style error code.

   Errors
       Returned errors may indicate the following problems:

       -ENOMEM
           Not enough memory to allocate an object.

       -EINVAL
           An invalid argument has been passed.

       -EBUSY
           A handler is already installed for this signal or the signal was not blocked previously.

       -ESTALE
           The event loop is already terminated.

       -ECHILD
           The event loop has been created in a different process, library or module instance.

       -EDOM
           The passed event source is not a signal event source.

NOTES

       Functions described here are available as a shared library, which can be compiled against and linked to
       with the libsystemd pkg-config(1) file.

       The code described here uses getenv(3), which is declared to be not multi-thread-safe. This means that
       the code calling the functions described here must not call setenv(3) from a parallel thread. It is
       recommended to only do calls to setenv() from an early phase of the program when no other threads have
       been started.

HISTORY

       sd_event_add_signal(), sd_event_signal_handler_t(), and sd_event_source_get_signal() were added in
       version 217.

SEE ALSO

       systemd(1), sd-event(3), sd_event_new(3), sd_event_now(3), sd_event_add_io(3), sd_event_add_time(3),
       sd_event_add_child(3), sd_event_add_inotify(3), sd_event_add_defer(3), sd_event_source_set_enabled(3),
       sd_event_source_set_description(3), sd_event_source_set_userdata(3), sd_event_source_set_floating(3),
       signal(7), signalfd(2), sigprocmask(2), pthread_sigmask(3)