Ubuntu Manpage: sd_event_source_set_floating, sd_event_source_get_floating

Provided by: libsystemd-dev_255.4-1ubuntu8.4_amd64

NAME

       sd_event_source_set_floating, sd_event_source_get_floating - Set or retrieve 'floating'
       state of event sources

SYNOPSIS

       #include <systemd/sd-event.h>

       int sd_event_source_set_floating(sd_event_source *source, int floating);

       int sd_event_source_get_floating(sd_event_source *source);

DESCRIPTION

sd_event_source_set_floating() takes a boolean and sets the 'floating' state of the
specified event source object. This is used to change the direction of reference counts
for the object and the event loop it is associated with. In non-floating mode, the event
source object holds a reference to the event loop object, but not vice versa. The creator
of the event source object must hold a reference to it as long as the source should exist.
In floating mode, the event loop holds a reference to the source object, and will decrease
the reference count when being freed. This means that a reference to the event loop should
be held to prevent both from being destroyed.

Various calls that allocate event source objects (i.e. sd_event_add_io(3),
sd_event_add_time(3) and similar) will automatically set an event source object to
'floating' mode if the caller passed NULL in the parameter used to return a reference to
the event source object. Nevertheless, it may be necessary to gain temporary access to the
source object, for example to adjust event source properties after allocation (e.g. its
priority or description string). In those cases the object may be created in non-floating
mode, and the returned reference used to adjust the properties, and the object marked as
floating afterwards, and the reference in the caller dropped.

sd_event_source_get_floating() may be used to query the current 'floating' state of the
event source object source. It returns zero if 'floating' mode is off, positive if it is
on.

RETURN VALUE

       On success, sd_event_source_set_floating() and sd_event_source_get_floating() 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.

           Added in version 244.

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

           Added in version 244.

NOTES

       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.

HISTORY