получение и освобождение объекта цикла событий (acquire and release an event loop object)
Имя (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
Синопсис (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);
Описание (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
{
__attribute__((cleanup(sd_event_unrefp))) sd_event *event = NULL;
int r;
...
r = sd_event_default(&event);
if (r < 0)
fprintf(stderr, "Failed to allocate event loop: %s\n", strerror(-r));
...
}
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.
Возвращаемое значение (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().
Примечание (Note)
These APIs are implemented as a shared library, which can be
compiled and linked to with the libsystemd pkg-config(1) file.
Смотри также (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)
Примечание (Note)
1. Clean-up Variable Attribute
https://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attributes.html
