|
NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | NOTES | SEE ALSO | NOTES | COLOPHON |
SD_EVENT_NEW(3) sd_event_new SD_EVENT_NEW(3)
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) or sd_event_add_defer(3), and then execute the
event loop using sd_event_run(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)
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.
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.
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().
These APIs are implemented as a shared library, which can be compiled
and linked to with the libsystemd pkg-config(1) file.
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_defer(3),
sd_event_add_post(3), sd_event_add_exit(3), sd_event_run(3),
gettid(2)
1. Clean-up Variable Attribute
https://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attributes.html
This page is part of the systemd (systemd system and service manager)
project. Information about the project can be found at
⟨http://www.freedesktop.org/wiki/Software/systemd⟩. If you have a bug
report for this manual page, see
⟨http://www.freedesktop.org/wiki/Software/systemd/#bugreports⟩. This
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⟨https://github.com/systemd/systemd.git⟩ on 2017-07-05. If you dis‐
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COLOPHON (which is not part of the original manual page), send a mail
to man-pages@man7.org
systemd 234 SD_EVENT_NEW(3)
Pages that refer to this page: sd-event(3), sd_event_add_child(3), sd_event_add_defer(3), sd_event_add_io(3), sd_event_add_signal(3), sd_event_add_time(3), sd_event_exit(3), sd_event_get_fd(3), sd_event_now(3), sd_event_run(3), sd_event_set_watchdog(3), sd_event_wait(3), systemd.directives(7), systemd.index(7)