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   sd_event_priority_normal    ( 3 )

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)