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NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | NOTES | HISTORY | SEE ALSO | COLOPHON |
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SD_EVENT...PRIORITY(3) sd_event_source_set_prioritySD_EVENT...PRIORITY(3)
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
#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);
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), 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 64-bit 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.
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,
library or module instance.
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
started.
sd_event_source_set_priority() and sd_event_source_get_priority()
were added in version 229.
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)
This page is part of the systemd (systemd system and service
manager) project. Information about the project can be found at
⟨http://www.freedesktop.org/wiki/Software/systemd⟩. If you have a
bug report for this manual page, see
⟨http://www.freedesktop.org/wiki/Software/systemd/#bugreports⟩.
This page was obtained from the project's upstream Git repository
⟨https://github.com/systemd/systemd.git⟩ on 2025-08-11. (At that
time, the date of the most recent commit that was found in the
repository was 2025-08-11.) 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
man-pages@man7.org
systemd 258~rc2 SD_EVENT...PRIORITY(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)
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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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