sd_event_source_set_priority(3) — Linux manual page


SD_EVEN...RIORITY(3)  sd_event_source_set_priority  SD_EVEN...RIORITY(3)

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 64-bit 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),
       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
       64-bit signed integer range is available for ordering event

       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

       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,
           library or module instance.

NOTES         top

       Functions described here are available as a shared library, which
       can be compiled against and linked to with the
       libsystemd pkg-config(1) file.

       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

HISTORY         top

       sd_event_source_set_priority() and sd_event_source_get_priority()
       were added in version 229.

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

       This page is part of the systemd (systemd system and service
       manager) project.  Information about the project can be found at
       ⟨⟩.  If you have
       a bug report for this manual page, see
       This page was obtained from the project's upstream Git repository
       ⟨⟩ on 2023-12-22.  (At that
       time, the date of the most recent commit that was found in the
       repository was 2023-12-22.)  If you discover any rendering
       problems in this HTML version of the page, or you believe there
       is a better or more up-to-date source for the page, or you have
       corrections or improvements to the information in this COLOPHON
       (which is not part of the original manual page), send a mail to

systemd 255                                         SD_EVEN...RIORITY(3)

Pages that refer to this page: sd_bus_attach_event(3)sd-event(3)sd_event_add_child(3)sd_event_add_defer(3)sd_event_add_inotify(3)sd_event_add_io(3)sd_event_add_time(3)sd_event_source_get_pending(3)sd_event_source_set_floating(3)sd_event_source_set_prepare(3)systemd.directives(7)systemd.index(7)