x SuSE Linux 13.1-RELEASE x
x SuSE Linux 13.1-RELEASEx
SD_EVENT_NEW(3) sd_event_new SD_EVENT_NEW(3)
NAME
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
SYNOPSIS
#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);
DESCRIPTION
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[1]. 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.
RETURN VALUE
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.
Errors
Returned errors may indicate the following problems:
-ENOMEM
Not enough memory to allocate the object.
-EMFILE
The maximum number of event loops has been allocated.
-ENXIO
sd_event_get_tid() was invoked on an event loop object that was not
allocated with sd_event_default().
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.
SEE ALSO
systemd(1), 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_run(3), gettid(2)
NOTES
1. Clean-up Variable Attribute
https://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attributes.html
systemd 254 SD_EVENT_NEW(3)
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