установите предварительный обратный вызов для источников событий (Set a preparation callback for event sources)
Имя (Name)
sd_event_source_set_prepare - Set a preparation callback for
event sources
Синопсис (Synopsis)
#include <systemd/sd-event.h>
int sd_event_source_set_prepare(sd_event_source *source,
sd_event_handler_t callback);
typedef int (*sd_event_handler_t)(sd_event_source *s,
void *userdata);
Описание (Description)
sd_event_source_set_prepare() may be used to set a preparation
callback for the event source object specified as source. The
callback function specified as callback will be invoked
immediately before the event loop goes to sleep to wait for
incoming events. It is invoked with the user data pointer passed
when the event source was created. The event source will be
disabled if the callback function returns a negative error code.
The callback function may be used to reconfigure the precise
events to wait for. If the callback parameter is passed as NULL
the callback function is reset.
Event source objects have no preparation callback associated when
they are first created with calls such as sd_event_add_io(3),
sd_event_add_time(3). Preparation callback functions are
supported for all event source types with the exception of those
created with sd_event_add_exit(3). Preparation callback functions
are dispatched in the order indicated by the event source's
priority field, as set with sd_event_source_set_priority(3).
Preparation callbacks of disabled event sources (see
sd_event_source_set_enabled(3)) are not invoked.
Возвращаемое значение (Return value)
On success, sd_event_source_set_prepare() returns a non-negative
integer. On failure, it returns a negative errno-style error
code.
Errors
Returned errors may indicate the following problems:
-EINVAL
source is not a valid pointer to an sd_event_source object.
-ESTALE
The event loop is already terminated.
-ENOMEM
Not enough memory.
-ECHILD
The event loop has been created in a different process.
-EDOM
The specified event source has been created with
sd_event_add_exit(3).
Примечание (Note)
These APIs are implemented as a shared library, which can be
compiled and linked to with the libsystemd pkg-config(1) file.
Смотри также (See also)
sd-event(3), sd_event_add_io(3), sd_event_add_time(3),
sd_event_add_signal(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_priority(3),
sd_event_source_set_userdata(3)
