SD_EVENT_SOURCE_SET_PRIORsd_event_source_set_prSD_EVENT_SOURCE_SET_PRIORITY(3)

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

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);

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.

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.

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

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)

systemd 252                                    SD_EVENT_SOURCE_SET_PRIORITY(3)

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