sd_event_add_signal
systemd
sd_event_add_signal
3
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
#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 signal7).
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
signalfd2 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_exit3 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 sigprocmask2 or
pthread_sigmask3). 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_enabled3.
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_failure3.
To destroy an event source object use
sd_event_source_unref3,
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_enabled3
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_exit3.
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.
See Also
systemd1,
sd-event3,
sd_event_new3,
sd_event_now3,
sd_event_add_io3,
sd_event_add_time3,
sd_event_add_child3,
sd_event_add_inotify3,
sd_event_add_defer3,
sd_event_source_set_enabled3,
sd_event_source_set_description3,
sd_event_source_set_userdata3,
sd_event_source_set_floating3,
signal7,
signalfd2,
sigprocmask2,
pthread_sigmask3