sd_event_source_get_priority(3) — Linux manual page



NAME         top

       sd_event_source_set_priority, sd_event_source_get_priority,
       SD_EVENT_PRIORITY_IDLE - Set or retrieve the priority of event

SYNOPSIS         top

       #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         top

       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_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         top

       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.

       Returned errors may indicate the following problems:

           source is not a valid pointer to an sd_event_source object.

           Not enough memory.

           The event loop is already terminated.

           The event loop has been created in a different process.

NOTES         top

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

SEE ALSO         top

       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)

COLOPHON         top

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       ⟨⟩.  This
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systemd 246                                  SD_EVENT_SOURCE_SET_PRIORITY(3)

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