x SuSE Linux 13.1-RELEASE x
x SuSE Linux 13.1-RELEASEx
SD_EVENT_GET_FD(3) sd_event_get_fd SD_EVENT_GET_FD(3)
NAME
sd_event_get_fd - Obtain a file descriptor to poll for event loop
events
SYNOPSIS
#include <systemd/sd-event.h>
int sd_event_get_fd(sd_event *event);
DESCRIPTION
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.
RETURN VALUE
On success, sd_event_get_fd() returns a non-negative file descriptor.
On failure, it returns a negative errno-style error code.
Errors
Returned errors may indicate the following problems:
-EINVAL
event is not a valid pointer to an sd_event structure.
-ECHILD
The event loop has been created in a different process, library or
module instance.
EXAMPLES
Example 1. Integration in the GLib event loop
/* SPDX-License-Identifier: MIT-0 */
#include <stdlib.h>
#include <glib.h>
#include <systemd/sd-event.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;
}
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
sd-event(3), sd_event_new(3), sd_event_wait(3), epoll_ctl(2), epoll(7)
systemd 254 SD_EVENT_GET_FD(3)
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