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) ; |
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.
On success, these functions return 0 or a positive integer. On failure, they return a negative errno-style error code.
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.
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.
sd_event_add_signal()
,
sd_event_signal_handler_t()
, and
sd_event_source_get_signal()
were added in version 217.
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)