1SD_EVENT_SOURCE_SET_PRIORIsTdY_(e3v)ent_source_set_priSoDr_iEtVyENT_SOURCE_SET_PRIORITY(3)
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NAME

6       sd_event_source_set_priority, sd_event_source_get_priority,
7       SD_EVENT_PRIORITY_IMPORTANT, SD_EVENT_PRIORITY_NORMAL,
8       SD_EVENT_PRIORITY_IDLE - Set or retrieve the priority of event sources
9

SYNOPSIS

11       #include <systemd/sd-event.h>
12
13       enum {
14               SD_EVENT_PRIORITY_IMPORTANT = -100,
15               SD_EVENT_PRIORITY_NORMAL = 0,
16               SD_EVENT_PRIORITY_IDLE = 100,
17       };
18
19       int sd_event_source_set_priority(sd_event_source *source,
20                                        int64_t priority);
21
22       int sd_event_source_get_priority(sd_event_source *source,
23                                        int64_t *priority);
24

DESCRIPTION

26       sd_event_source_set_priority() may be used to set the priority for the
27       event source object specified as source. The priority is specified as
28       an arbitrary signed 64bit integer. The priority is initialized to
29       SD_EVENT_PRIORITY_NORMAL (0) when the event source is allocated with a
30       call such as sd_event_add_io(3) or sd_event_add_time(3), and may be
31       changed with this call. If multiple event sources have seen events at
32       the same time, they are dispatched in the order indicated by the event
33       sources' priorities. Event sources with smaller priority values are
34       dispatched first. As well-known points of reference, the constants
35       SD_EVENT_PRIORITY_IMPORTANT (-100), SD_EVENT_PRIORITY_NORMAL (0) and
36       SD_EVENT_PRIORITY_IDLE (100) may be used to indicate event sources that
37       shall be dispatched early, normally or late. It is recommended to
38       specify priorities based on these definitions, and relative to them —
39       however, the full 64bit signed integer range is available for ordering
40       event sources.
41
42       Priorities define the order in which event sources that have seen
43       events are dispatched. Care should be taken to ensure that
44       high-priority event sources (those with negative priority values
45       assigned) do not cause starvation of low-priority event sources (those
46       with positive priority values assigned).
47
48       The order in which event sources with the same priority are dispatched
49       is undefined, but the event loop generally tries to dispatch them in
50       the order it learnt about events on them. As the backing kernel
51       primitives do not provide accurate information about the order in which
52       events occurred this is not necessarily reliable. However, it is
53       guaranteed that if events are seen on multiple same-priority event
54       sources at the same time, each one is not dispatched again until all
55       others have been dispatched once. This behavior guarantees that within
56       each priority particular event sources do not starve or dominate the
57       event loop.
58
59       The priority of event sources may be changed at any time of their
60       lifetime, with the exception of inotify event sources (i.e. those
61       created with sd_event_add_inotify(3)) whose priority may only be
62       changed in the time between their initial creation and the first
63       subsequent event loop iteration.
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65       sd_event_source_get_priority() may be used to query the current
66       priority assigned to the event source object source.
67

RETURN VALUE

69       On success, sd_event_source_set_priority() and
70       sd_event_source_get_priority() return a non-negative integer. On
71       failure, they return a negative errno-style error code.
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73   Errors
74       Returned errors may indicate the following problems:
75
76       -EINVAL
77           source is not a valid pointer to an sd_event_source object.
78
79       -ENOMEM
80           Not enough memory.
81
82       -ESTALE
83           The event loop is already terminated.
84
85       -ECHILD
86           The event loop has been created in a different process.
87

NOTES

89       These APIs are implemented as a shared library, which can be compiled
90       and linked to with the libsystemd pkg-config(1) file.
91

SEE ALSO

93       sd-event(3), sd_event_add_io(3), sd_event_add_time(3),
94       sd_event_add_signal(3), sd_event_add_child(3), sd_event_add_inotify(3),
95       sd_event_add_defer(3)
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98
99systemd 243                                    SD_EVENT_SOURCE_SET_PRIORITY(3)
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