добавить источник событий ввода-вывода в цикл событий (add an I/O event source to an event loop)
Имя (Name)
sd_event_add_io, sd_event_source_get_io_events,
sd_event_source_set_io_events, sd_event_source_get_io_revents,
sd_event_source_get_io_fd, sd_event_source_set_io_fd,
sd_event_source_get_io_fd_own, sd_event_source_set_io_fd_own,
sd_event_source, sd_event_io_handler_t - Add an I/O event source
to an event loop
Синопсис (Synopsis)
#include <systemd/sd-event.h>
typedef struct sd_event_source sd_event_source;
typedef int (*sd_event_io_handler_t)(sd_event_source *s, int fd,
uint32_t revents,
void *userdata);
int sd_event_add_io(sd_event *event, sd_event_source **source,
int fd, uint32_t events,
sd_event_io_handler_t handler,
void *userdata);
int sd_event_source_get_io_events(sd_event_source *source,
uint32_t *events);
int sd_event_source_set_io_events(sd_event_source *source,
uint32_t events);
int sd_event_source_get_io_revents(sd_event_source *source,
uint32_t *revents);
int sd_event_source_get_io_fd(sd_event_source *source);
int sd_event_source_set_io_fd(sd_event_source *source, int fd);
int sd_event_source_get_io_fd_own(sd_event_source *source);
int sd_event_source_set_io_fd_own(sd_event_source *source,
int b);
Описание (Description)
sd_event_add_io() adds a new I/O event source to an event loop.
The event loop object is specified in the event parameter, the
event source object is returned in the source parameter. The fd
parameter takes the UNIX file descriptor to watch, which may
refer to a socket, a FIFO, a message queue, a serial connection,
a character device, or any other file descriptor compatible with
Linux epoll(7). The events parameter takes a bit mask of events
to watch for, a combination of the following event flags:
EPOLLIN, EPOLLOUT, EPOLLRDHUP, EPOLLPRI, and EPOLLET, see
epoll_ctl(2) for details. The handler shall reference a function
to call when the event source is triggered. The userdata pointer
will be passed to the handler function, and may be chosen freely
by the caller. The handler will also be passed the file
descriptor the event was seen on, as well as the actual event
flags. It's generally a subset of the events watched, however may
additionally include EPOLLERR and EPOLLHUP.
By default, an event source will stay enabled continuously
(SD_EVENT_ON), but this may be changed with
sd_event_source_set_enabled(3). If the handler function returns a
negative error code, it will be disabled after the invocation,
even if the SD_EVENT_ON mode was requested before. Note that an
event source set to SD_EVENT_ON will fire continuously unless
data is read from or written to the file descriptor to reset the
mask of events seen.
Setting the I/O event mask to watch for to 0 does not mean that
the event source won't be triggered anymore, as EPOLLHUP and
EPOLLERR may be triggered even with a zero event mask. To
temporarily disable an I/O event source use
sd_event_source_set_enabled(3) with SD_EVENT_OFF instead.
To destroy an event source object use sd_event_source_unref(3),
but note that the event source is only removed from the event
loop when all references to the event source are dropped. To make
sure an event source does not fire anymore, even if it is still
referenced, disable the event source using
sd_event_source_set_enabled(3) with SD_EVENT_OFF.
If the second parameter of sd_event_add_io() is NULL no reference
to the event source object is returned. In this case the event
source is considered "floating", and will be destroyed implicitly
when the event loop itself is destroyed.
If the handler to sd_event_add_io() is NULL, and the event source
fires, this will be considered a request to exit the event loop.
In this case, the userdata parameter, cast to an integer, is
passed as the exit code parameter to sd_event_exit(3).
Note that this call does not take possession of the file
descriptor passed in, ownership (and thus the duty to close it
when it is no longer needed) remains with the caller. However,
with the sd_event_source_set_io_fd_own() call (see below) the
event source may optionally take ownership of the file descriptor
after the event source has been created. In that case the file
descriptor is closed automatically as soon as the event source is
released.
It is recommended to use sd_event_add_io() only in conjunction
with file descriptors that have O_NONBLOCK set, to ensure that
all I/O operations from invoked handlers are properly
asynchronous and non-blocking. Using file descriptors without
O_NONBLOCK might result in unexpected starvation of other event
sources. See fcntl(2) for details on enabling O_NONBLOCK mode.
sd_event_source_get_io_events() retrieves the configured mask of
watched I/O events of an event source created previously with
sd_event_add_io(). It takes the event source object and a pointer
to a variable to store the mask in.
sd_event_source_set_io_events() configures the mask of watched
I/O events of an event source created previously with
sd_event_add_io(). It takes the event source object and the new
event mask.
sd_event_source_get_io_revents() retrieves the I/O event mask of
currently seen but undispatched events from an event source
created previously with sd_event_add_io(). It takes the event
source object and a pointer to a variable to store the event mask
in. When called from a handler function on the handler's event
source object this will return the same mask as passed to the
handler's revents parameter. This call is primarily useful to
check for undispatched events of an event source from the handler
of an unrelated (possibly higher priority) event source. Note the
relation between sd_event_source_get_pending() and
sd_event_source_get_io_revents(): both functions will report
non-zero results when there's an event pending for the event
source, but the former applies to all event source types, the
latter only to I/O event sources.
sd_event_source_get_io_fd() retrieves the UNIX file descriptor of
an event source created previously with sd_event_add_io(). It
takes the event source object and returns the non-negative file
descriptor or a negative error number on error (see below).
sd_event_source_set_io_fd() changes the UNIX file descriptor of
an I/O event source created previously with sd_event_add_io(). It
takes the event source object and the new file descriptor.
sd_event_source_set_io_fd_own() controls whether the file
descriptor of the event source shall be closed automatically when
the event source is freed, i.e. whether it shall be considered
'owned' by the event source object. By default it is not closed
automatically, and the application has to do this on its own. The
b parameter is a boolean parameter: if zero, the file descriptor
is not closed automatically when the event source is freed,
otherwise it is closed.
sd_event_source_get_io_fd_own() may be used to query the current
setting of the file descriptor ownership boolean flag as set with
sd_event_source_set_io_fd_own(). It returns positive if the file
descriptor is closed automatically when the event source is
destroyed, zero if not, and negative on error.
Возвращаемое значение (Return value)
On success, these functions return 0 or a positive integer. On
failure, they return a negative errno-style error code.
Errors
Returned values may indicate the following problems:
-ENOMEM
Not enough memory to allocate an object.
-EINVAL
An invalid argument has been passed.
-ESTALE
The event loop is already terminated.
-ECHILD
The event loop has been created in a different process.
-EDOM
The passed event source is not an I/O event source.
Примечание (Note)
These APIs are implemented as a shared library, which can be
compiled and linked to with the libsystemd pkg-config(1) file.
Смотри также (See also)
systemd(1), sd-event(3), sd_event_new(3), sd_event_now(3),
sd_event_add_time(3), sd_event_add_signal(3),
sd_event_add_child(3), sd_event_add_inotify(3),
sd_event_add_defer(3), sd_event_source_set_enabled(3),
sd_event_source_set_priority(3), sd_event_source_set_userdata(3),
sd_event_source_set_description(3),
sd_event_source_get_pending(3), sd_event_source_set_floating(3),
epoll_ctl(2), epoll(7)
