установить или получить приоритет источников событий (set or retrieve the priority of event sources)
Имя (Name)
sd_event_source_set_priority, sd_event_source_get_priority,
SD_EVENT_PRIORITY_IMPORTANT, SD_EVENT_PRIORITY_NORMAL,
SD_EVENT_PRIORITY_IDLE - Set or retrieve the priority of event
sources
Синопсис (Synopsis)
#include <systemd/sd-event.h>
enum {
SD_EVENT_PRIORITY_IMPORTANT = -100,
SD_EVENT_PRIORITY_NORMAL = 0,
SD_EVENT_PRIORITY_IDLE = 100,
};
int sd_event_source_set_priority(sd_event_source *source,
int64_t priority);
int sd_event_source_get_priority(sd_event_source *source,
int64_t *priority);
Описание (Description)
sd_event_source_set_priority() may be used to set the priority
for the event source object specified as source. The priority is
specified as an arbitrary signed 64bit integer. The priority is
initialized to SD_EVENT_PRIORITY_NORMAL (0) when the event source
is allocated with a call such as sd_event_add_io(3) or
sd_event_add_time(3), and may be changed with this call. If
multiple event sources have seen events at the same time, they
are dispatched in the order indicated by the event sources'
priorities. Event sources with smaller priority values are
dispatched first. As well-known points of reference, the
constants SD_EVENT_PRIORITY_IMPORTANT (-100),
SD_EVENT_PRIORITY_NORMAL (0) and SD_EVENT_PRIORITY_IDLE (100) may
be used to indicate event sources that shall be dispatched early,
normally or late. It is recommended to specify priorities based
on these definitions, and relative to them — however, the full
64bit signed integer range is available for ordering event
sources.
Priorities define the order in which event sources that have seen
events are dispatched. Care should be taken to ensure that
high-priority event sources (those with negative priority values
assigned) do not cause starvation of low-priority event sources
(those with positive priority values assigned).
The order in which event sources with the same priority are
dispatched is undefined, but the event loop generally tries to
dispatch them in the order it learnt about events on them. As the
backing kernel primitives do not provide accurate information
about the order in which events occurred this is not necessarily
reliable. However, it is guaranteed that if events are seen on
multiple same-priority event sources at the same time, each one
is not dispatched again until all others have been dispatched
once. This behavior guarantees that within each priority
particular event sources do not starve or dominate the event
loop.
The priority of event sources may be changed at any time of their
lifetime, with the exception of inotify event sources (i.e. those
created with sd_event_add_inotify(3)) whose priority may only be
changed in the time between their initial creation and the first
subsequent event loop iteration.
sd_event_source_get_priority() may be used to query the current
priority assigned to the event source object source.
Возвращаемое значение (Return value)
On success, sd_event_source_set_priority() and
sd_event_source_get_priority() return a non-negative integer. On
failure, they return 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.
-ENOMEM
Not enough memory.
-ESTALE
The event loop is already terminated.
-ECHILD
The event loop has been created in a different process.
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)
