sd_event_get_fd — Obtain a file descriptor to poll for event loop events
#include <systemd/sd-event.h>
int sd_event_get_fd( | sd_event *event); |
sd_event_get_fd() returns the file
descriptor that an event loop object returned by the
sd_event_new(3)
function uses to wait for events. This file descriptor may itself
be polled for
POLLIN/EPOLLIN
events. This makes it possible to embed an
sd-event(3)
event loop into another, possibly foreign, event loop.
The returned file descriptor refers to an epoll(7) object. It is recommended not to alter it by invoking epoll_ctl(2) on it, in order to avoid interference with the event loop's inner logic and assumptions.
On success, sd_event_get_fd() returns a
non-negative file descriptor. On failure, it returns a negative
errno-style error code.
Example 1. Integration in the GLib event loop
/***
Copyright 2014 Tom Gundersen
Permission is hereby granted, free of charge, to any person
obtaining a copy of this software and associated documentation files
(the "Software"), to deal in the Software without restriction,
including without limitation the rights to use, copy, modify, merge,
publish, distribute, sublicense, and/or sell copies of the Software,
and to permit persons to whom the Software is furnished to do so,
subject to the following conditions:
The above copyright notice and this permission notice shall be
included in all copies or substantial portions of the Software.
THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
SOFTWARE.
***/
#include <stdlib.h>
typedef struct SDEventSource {
GSource source;
GPollFD pollfd;
sd_event *event;
} SDEventSource;
static gboolean event_prepare(GSource *source, gint *timeout_) {
return sd_event_prepare(((SDEventSource *)source)->event) > 0;
}
static gboolean event_check(GSource *source) {
return sd_event_wait(((SDEventSource *)source)->event, 0) > 0;
}
static gboolean event_dispatch(GSource *source, GSourceFunc callback, gpointer user_data) {
return sd_event_dispatch(((SDEventSource *)source)->event) > 0;
}
static void event_finalize(GSource *source) {
sd_event_unref(((SDEventSource *)source)->event);
}
static GSourceFuncs event_funcs = {
.prepare = event_prepare,
.check = event_check,
.dispatch = event_dispatch,
.finalize = event_finalize,
};
GSource *g_sd_event_create_source(sd_event *event) {
SDEventSource *source;
source = (SDEventSource *)g_source_new(&event_funcs, sizeof(SDEventSource));
source->event = sd_event_ref(event);
source->pollfd.fd = sd_event_get_fd(event);
source->pollfd.events = G_IO_IN | G_IO_HUP | G_IO_ERR;
g_source_add_poll((GSource *)source, &source->pollfd);
return (GSource *)source;
}
These APIs are implemented as a shared
library, which can be compiled and linked to with the
libsystemd pkg-config(1)
file.