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)