Provided by: libsystemd-dev_256.5-2ubuntu3.1_amd64
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.
HISTORY
sd_event_get_fd() was added in version 217.
SEE ALSO
sd-event(3), sd_event_new(3), sd_event_wait(3), epoll_ctl(2), epoll(7)