| SD_EVENT_SOURCE_SET_PREPARE(3) | sd_event_source_set_prepare | SD_EVENT_SOURCE_SET_PREPARE(3) |
.SH "NAME" sd_event_source_set_prepare - Set a preparation callback
for event sources
.SH "SYNOPSIS"
#include <systemd/sd-event.h>
.HP 768u int
sd_event_source_set_prepare(sd_event_source *source,
sd_event_handler_t callback);
.HP 816u typedef int
(*sd_event_handler_t)(sd_event_source *s,
void *userdata);
.SH "DESCRIPTION"
.PP 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.
.PP 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.
.SH "RETURN VALUE"
.PP On success, sd_event_source_set_prepare() returns a non-negative
integer. On failure, it returns a negative errno-style error code.
.SS "Errors"
.PP Returned errors may indicate the following problems:
.PP -EINVAL
source is not a valid pointer to an sd_event_source object.
.RE
.PP -ESTALE
The event loop is already terminated.
.RE
.PP -ENOMEM
Not enough memory.
.RE
.PP -ECHILD
The event loop has been created in a different process, library or module
instance.
.RE
.PP -EDOM
The specified event source has been created with
sd_event_add_exit(3).
.RE
.SH "NOTES"
.PP Functions described here are available as a shared library, which can be
compiled against and linked to with the
libsystemd pkg-config(1) file.
.PP All functions listed here are thread-agnostic and only a single thread
may operate on a given object at any given time. Different threads may
access the same object at different times. Multiple independent objects may
be used from different threads in parallel.
.PP 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.
.SH "HISTORY"
.PP sd_event_source_set_prepare() and sd_event_handler_t() were
added in version 229.
.SH "SEE ALSO"
.PP 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)
| systemd 262.2 |