SD_EVENT_SOURCE_SET_PREPARE - Online Linux Manual PageSection : 3
Updated :
Source : systemd 250
Note : sd_event_source_set_prepare

NAMEsd_event_source_set_prepare − Set a preparation callback for event sources

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);

DESCRIPTIONsd_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​.

RETURN VALUEOn success, sd_event_source_set_prepare() returns a non−negative integer​. On failure, it returns a negative errno−style error code​.

ErrorsReturned 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)​.

NOTESThese APIs are implemented as a shared library, which can be compiled and linked to with the libsystemd ​pkg-config(1) file​.

SEE ALSOsd-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)
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