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 will be unblocked by this call,
       and must be blocked before this function is called in all threads (using sigprocmask(2)). If the handler
       is not specified (handler is NULL), a default handler which causes the program to exit cleanly will be
       used.

       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.

       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_defer(3), sd_event_source_set_enabled(3),
       sd_event_source_set_description(3), sd_event_source_set_userdata(3), signal(7), signalfd(2)