sd_event_source_set_prepare(3) — Linux manual page


SD_EVEN..._PREPARE(3)  sd_event_source_set_prepare SD_EVEN..._PREPARE(3)

NAME         top

       sd_event_source_set_prepare - Set a preparation callback for
       event sources

SYNOPSIS         top

       #include <systemd/sd-event.h>

       int sd_event_source_set_prepare(sd_event_source *source,
                                       sd_event_handler_t callback);

       typedef int (*sd_event_handler_t)(sd_event_source *s,
                                         void *userdata);

DESCRIPTION         top

       sd_event_source_set_prepare() may be used to set a preparation
       callback for the event source object specified as source. The
       callback function specified as callback will be invoked
       immediately before the event loop goes to sleep to wait for
       incoming events. It is invoked with the user data pointer passed
       when the event source was created. The event source will be
       disabled if the callback function returns a negative error code.
       The callback function may be used to reconfigure the precise
       events to wait for. If the callback parameter is passed as NULL
       the callback function is reset.

       Event source objects have no preparation callback associated when
       they are first created with calls such as sd_event_add_io(3),
       sd_event_add_time(3). Preparation callback functions are
       supported for all event source types with the exception of those
       created with sd_event_add_exit(3). Preparation callback functions
       are dispatched in the order indicated by the event source's
       priority field, as set with sd_event_source_set_priority(3).
       Preparation callbacks of disabled event sources (see
       sd_event_source_set_enabled(3)) are not invoked.

RETURN VALUE         top

       On success, sd_event_source_set_prepare() returns a non-negative
       integer. On failure, it returns a negative errno-style error

       Returned errors may indicate the following problems:

           source is not a valid pointer to an sd_event_source object.

           The event loop is already terminated.

           Not enough memory.

           The event loop has been created in a different process,
           library or module instance.

           The specified event source has been created with

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_prepare() and sd_event_handler_t() 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),
       sd_event_source_set_enabled(3), sd_event_source_set_priority(3),

COLOPHON         top

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       This page was obtained from the project's upstream Git repository
       ⟨⟩ on 2024-06-14.  (At that
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systemd 257~devel                                  SD_EVEN..._PREPARE(3)

Pages that refer to this page: sd-event(3)sd_event_wait(3)systemd.directives(7)systemd.index(7)