sd_event_new, sd_event_default, sd_event_ref, sd_event_unref, sd_event_unrefp, sd_event_get_tid, sd_event — Acquire and release an event loop object
#include <systemd/sd-event.h>
typedef struct sd_event sd_event;
int sd_event_new( | sd_event **event) ; |
int sd_event_default( | sd_event **event) ; |
sd_event *sd_event_ref( | sd_event *event) ; |
sd_event *sd_event_unref( | sd_event *event) ; |
void sd_event_unrefp( | sd_event **event) ; |
int sd_event_get_tid( | sd_event *event, |
pid_t *tid) ; |
sd_event_new()
allocates a new event
loop object. The event loop object is returned in the
event
parameter. After use, drop
the returned reference with
sd_event_unref()
. When the last reference is
dropped, the object is freed.
sd_event_default()
acquires a reference
to the default event loop object of the calling thread, possibly
allocating a new object if no default event loop object has been
allocated yet for the thread. After use, drop the returned
reference with sd_event_unref()
. When the
last reference is dropped, the event loop is freed. If this
function is called while the object returned from a previous call
from the same thread is still referenced, the same object is
returned again, but the reference is increased by one. It is
recommended to use this call instead of
sd_event_new()
in order to share event loop
objects between various components that are dispatched in the same
thread. All threads have exactly either zero or one default event loop
objects associated, but never more.
After allocating an event loop object, add event sources to it with 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_add_post(3) or sd_event_add_exit(3), and then execute the event loop using sd_event_loop(3).
sd_event_ref()
increases the reference
count of the specified event loop object by one.
sd_event_unref()
decreases the
reference count of the specified event loop object by one. If
the count hits zero, the object is freed. Note that it
is freed regardless of whether it is the default event loop object for a
thread or not. This means that allocating an event loop with
sd_event_default()
, then releasing it, and
then acquiring a new one with
sd_event_default()
will result in two
distinct objects. Note that, in order to free an event loop object,
all remaining event sources of the event loop also need to be
freed as each keeps a reference to it.
sd_event_unrefp()
is similar to
sd_event_unref()
but takes a pointer to a
pointer to an sd_event object. This call is useful in
conjunction with GCC's and LLVM's Clean-up
Variable Attribute. Note that this function is defined as
inline function. Use a declaration like the following,
in order to allocate an event loop object that is freed
automatically as the code block is left:
{ __attribute__((cleanup(sd_event_unrefp))) sd_event *event = NULL; int r; … r = sd_event_default(&event); if (r < 0) { errno = -r; fprintf(stderr, "Failed to allocate event loop: %m\n"); } … }
sd_event_ref()
,
sd_event_unref()
and
sd_event_unrefp()
execute no operation if the
passed in event loop object is NULL
.
sd_event_get_tid()
retrieves the thread
identifier ("TID") of the thread the specified event loop object
is associated with. This call is only supported for event loops
allocated with sd_event_default()
, and
returns the identifier for the thread the event loop is the
default event loop of. See gettid(2)
for more information on thread identifiers.
On success, sd_event_new()
, sd_event_default()
and
sd_event_get_tid()
return 0 or a positive integer. On failure, they return a
negative errno-style error code. sd_event_ref()
always returns a pointer to the
event loop object passed in. sd_event_unref()
always returns
NULL
.
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_new()
,
sd_event_default()
,
sd_event_ref()
, and
sd_event_unref()
were added in version 213.
sd_event_unrefp()
and
sd_event_get_tid()
were added in version 229.