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   sd_event_get_fd    ( 3 )

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Имя (Name)

sd_event_get_fd - Obtain a file descriptor to poll for event loop events

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Синопсис (Synopsis)

#include <systemd/sd-event.h>

int sd_event_get_fd(sd_event *event);

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Описание (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.

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Возвращаемое значение (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.

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Примеры (Examples)

Example 1. Integration in the GLib event loop

           /* SPDX-License-Identifier: MIT */

           #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;
           }

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Примечание (Note)

These APIs are implemented as a shared library, which can be compiled and linked to with the libsystemd pkg-config(1) file.

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Смотри также (See also)

sd-event(3), sd_event_new(3), sd_event_wait(3), epoll_ctl(2), epoll(7)

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