NAME

       sd_event_add_signal, sd_event_source_get_signal, sd_event_signal_handler_t - 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;

       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 must reference a function to call when the
       signal is received or be 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.

       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)).

       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 be disabled after the invocation, even if the SD_EVENT_ON mode was requested
       before.

       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.

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

NOTES

       These APIs are implemented as a shared library, which can be compiled and linked to with
       the libsystemd pkg-config(1) file.

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)