Provided by: libwayland-doc_1.21.0-1_all 
NAME
wl_display - Represents a connection to the compositor and acts as a proxy to the
wl_display singleton object.
SYNOPSIS
#include <wayland-client-core.h>
Public Member Functions
struct wl_client * wl_client_create (struct wl_display *display, int fd)
struct wl_display * wl_display_create (void)
void wl_display_destroy (struct wl_display *display)
void wl_display_set_global_filter (struct wl_display *display,
wl_display_global_filter_func_t filter, void *data)
uint32_t wl_display_get_serial (struct wl_display *display)
uint32_t wl_display_next_serial (struct wl_display *display)
void wl_display_destroy_clients (struct wl_display *display)
int wl_display_add_socket_fd (struct wl_display *display, int sock_fd)
int wl_display_add_socket (struct wl_display *display, const char *name)
struct wl_protocol_logger * wl_display_add_protocol_logger (struct wl_display *display,
wl_protocol_logger_func_t func, void *user_data)
uint32_t * wl_display_add_shm_format (struct wl_display *display, uint32_t format)
struct wl_list * wl_display_get_client_list (struct wl_display *display)
struct wl_event_queue * wl_display_create_queue (struct wl_display *display)
struct wl_display * wl_display_connect_to_fd (int fd)
struct wl_display * wl_display_connect (const char *name)
void wl_display_disconnect (struct wl_display *display)
int wl_display_get_fd (struct wl_display *display)
int wl_display_roundtrip_queue (struct wl_display *display, struct wl_event_queue *queue)
int wl_display_roundtrip (struct wl_display *display)
int wl_display_read_events (struct wl_display *display)
int wl_display_prepare_read_queue (struct wl_display *display, struct wl_event_queue
*queue)
int wl_display_prepare_read (struct wl_display *display)
void wl_display_cancel_read (struct wl_display *display)
int wl_display_dispatch_queue (struct wl_display *display, struct wl_event_queue *queue)
int wl_display_dispatch_queue_pending (struct wl_display *display, struct wl_event_queue
*queue)
int wl_display_dispatch (struct wl_display *display)
int wl_display_dispatch_pending (struct wl_display *display)
int wl_display_get_error (struct wl_display *display)
uint32_t wl_display_get_protocol_error (struct wl_display *display, const struct
wl_interface **interface, uint32_t *id)
int wl_display_flush (struct wl_display *display)
Data Fields
struct wl_event_loop * loop
int run
uint32_t id
uint32_t serial
struct wl_list registry_resource_list
struct wl_list global_list
struct wl_list socket_list
struct wl_list client_list
struct wl_list protocol_loggers
struct wl_priv_signal destroy_signal
struct wl_priv_signal create_client_signal
struct wl_array additional_shm_formats
wl_display_global_filter_func_t global_filter
void * global_filter_data
int terminate_efd
struct wl_event_source * term_source
Detailed Description
Represents a connection to the compositor and acts as a proxy to the wl_display singleton
object.
A wl_display object represents a client connection to a Wayland compositor. It is created
with either wl_display_connect() or wl_display_connect_to_fd(). A connection is terminated
using wl_display_disconnect().
A wl_display is also used as the wl_proxy for the wl_display singleton object on the
compositor side.
A wl_display object handles all the data sent from and to the compositor. When a wl_proxy
marshals a request, it will write its wire representation to the display's write buffer.
The data is sent to the compositor when the client calls wl_display_flush().
Incoming data is handled in two steps: queueing and dispatching. In the queue step, the
data coming from the display fd is interpreted and added to a queue. On the dispatch step,
the handler for the incoming event set by the client on the corresponding wl_proxy is
called.
A wl_display has at least one event queue, called the default queue. Clients can create
additional event queues with wl_display_create_queue() and assign wl_proxy's to it. Events
occurring in a particular proxy are always queued in its assigned queue. A client can
ensure that a certain assumption, such as holding a lock or running from a given thread,
is true when a proxy event handler is called by assigning that proxy to an event queue and
making sure that this queue is only dispatched when the assumption holds.
The default queue is dispatched by calling wl_display_dispatch(). This will dispatch any
events queued on the default queue and attempt to read from the display fd if it's empty.
Events read are then queued on the appropriate queues according to the proxy assignment.
A user created queue is dispatched with wl_display_dispatch_queue(). This function behaves
exactly the same as wl_display_dispatch() but it dispatches given queue instead of the
default queue.
A real world example of event queue usage is Mesa's implementation of eglSwapBuffers() for
the Wayland platform. This function might need to block until a frame callback is
received, but dispatching the default queue could cause an event handler on the client to
start drawing again. This problem is solved using another event queue, so that only the
events handled by the EGL code are dispatched during the block.
This creates a problem where a thread dispatches a non-default queue, reading all the data
from the display fd. If the application would call poll(2) after that it would block, even
though there might be events queued on the default queue. Those events should be
dispatched with wl_display_dispatch_pending() or wl_display_dispatch_queue_pending()
before flushing and blocking.
Member Function Documentation
struct wl_client * wl_client_create (struct wl_display * display, int fd)
Create a client for the given file descriptor
Parameters
display The display object
fd The file descriptor for the socket to the client
Returns
The new client object or NULL on failure.
Given a file descriptor corresponding to one end of a socket, this function will create a
wl_client struct and add the new client to the compositors client list. At that point, the
client is initialized and ready to run, as if the client had connected to the servers
listening socket. When the client eventually sends requests to the compositor, the
wl_client argument to the request handler will be the wl_client returned from this
function.
The other end of the socket can be passed to wl_display_connect_to_fd() on the client side
or used with the WAYLAND_SOCKET environment variable on the client side.
Listeners added with wl_display_add_client_created_listener() will be notified by this
function after the client is fully constructed.
On failure this function sets errno accordingly and returns NULL.
struct wl_protocol_logger * wl_display_add_protocol_logger (struct wl_display * display,
wl_protocol_logger_func_t func, void * user_data)
Adds a new protocol logger.
When a new protocol message arrives or is sent from the server all the protocol logger
functions will be called, carrying the user_data pointer, the type of the message (request
or event) and the actual message. The lifetime of the messages passed to the logger
function ends when they return so the messages cannot be stored and accessed later.
errno is set on error.
Parameters
display The display object
func The function to call to log a new protocol message
user_data The user data pointer to pass to func
Returns
The protol logger object on success, NULL on failure.
See also
wl_protocol_logger_destroy
uint32_t * wl_display_add_shm_format (struct wl_display * display, uint32_t format)
Add support for a wl_shm pixel format
Parameters
display The display object
format The wl_shm pixel format to advertise
Returns
A pointer to the wl_shm format that was added to the list or NULL if adding it to the
list failed.
Add the specified wl_shm format to the list of formats the wl_shm object advertises when a
client binds to it. Adding a format to the list means that clients will know that the
compositor supports this format and may use it for creating wl_shm buffers. The compositor
must be able to handle the pixel format when a client requests it.
The compositor by default supports WL_SHM_FORMAT_ARGB8888 and WL_SHM_FORMAT_XRGB8888.
int wl_display_add_socket (struct wl_display * display, const char * name)
Add a socket to Wayland display for the clients to connect.
Parameters
display Wayland display to which the socket should be added.
name Name of the Unix socket.
Returns
0 if success. -1 if failed.
This adds a Unix socket to Wayland display which can be used by clients to connect to
Wayland display.
If NULL is passed as name, then it would look for WAYLAND_DISPLAY env variable for the
socket name. If WAYLAND_DISPLAY is not set, then default wayland-0 is used.
If the socket name is a relative path, the Unix socket will be created in the directory
pointed to by environment variable XDG_RUNTIME_DIR. If XDG_RUNTIME_DIR is invalid or not
set, then this function fails and returns -1.
If the socket name is an absolute path, then it is used as-is for the the Unix socket.
The length of the computed socket path must not exceed the maximum length of a Unix socket
path. The function also fails if the user does not have write permission in the directory
or if the path is already in use.
int wl_display_add_socket_fd (struct wl_display * display, int sock_fd)
Add a socket with an existing fd to Wayland display for the clients to connect.
Parameters
display Wayland display to which the socket should be added.
sock_fd The existing socket file descriptor to be used
Returns
0 if success. -1 if failed.
The existing socket fd must already be created, opened, and locked. The fd must be
properly set to CLOEXEC and bound to a socket file with both bind() and listen() already
called.
void wl_display_cancel_read (struct wl_display * display)
Cancel read intention on display's fd
Parameters
display The display context object
After a thread successfully called wl_display_prepare_read() it must either call
wl_display_read_events() or wl_display_cancel_read(). If the threads do not follow this
rule it will lead to deadlock.
See also
wl_display_prepare_read(), wl_display_read_events()
struct wl_display * wl_display_connect (const char * name)
Connect to a Wayland display
Parameters
name Name of the Wayland display to connect to
Returns
A wl_display object or NULL on failure
Connect to the Wayland display named name. If name is NULL, its value will be replaced
with the WAYLAND_DISPLAY environment variable if it is set, otherwise display 'wayland-0'
will be used.
If WAYLAND_SOCKET is set, it's interpreted as a file descriptor number referring to an
already opened socket. In this case, the socket is used as-is and name is ignored.
If name is a relative path, then the socket is opened relative to the XDG_RUNTIME_DIR
directory.
If name is an absolute path, then that path is used as-is for the location of the socket
at which the Wayland server is listening; no qualification inside XDG_RUNTIME_DIR is
attempted.
If name is NULL and the WAYLAND_DISPLAY environment variable is set to an absolute
pathname, then that pathname is used as-is for the socket in the same manner as if name
held an absolute path. Support for absolute paths in name and WAYLAND_DISPLAY is present
since Wayland version 1.15.
struct wl_display * wl_display_connect_to_fd (int fd)
Connect to Wayland display on an already open fd
Parameters
fd The fd to use for the connection
Returns
A wl_display object or NULL on failure
The wl_display takes ownership of the fd and will close it when the display is destroyed.
The fd will also be closed in case of failure.
struct wl_display * wl_display_create (void)
Create Wayland display object.
Returns
The Wayland display object. Null if failed to create
This creates the wl_display object.
struct wl_event_queue * wl_display_create_queue (struct wl_display * display)
Create a new event queue for this display
Parameters
display The display context object
Returns
A new event queue associated with this display or NULL on failure.
void wl_display_destroy (struct wl_display * display)
Destroy Wayland display object.
Parameters
display The Wayland display object which should be destroyed.
Returns
None.
This function emits the wl_display destroy signal, releases all the sockets added to this
display, free's all the globals associated with this display, free's memory of additional
shared memory formats and destroy the display object.
See also
wl_display_add_destroy_listener
void wl_display_destroy_clients (struct wl_display * display)
Destroy all clients connected to the display
Parameters
display The display object
This function should be called right before wl_display_destroy() to ensure all client
resources are closed properly. Destroying a client from within
wl_display_destroy_clients() is safe, but creating one will leak resources and raise a
warning.
void wl_display_disconnect (struct wl_display * display)
Close a connection to a Wayland display
Parameters
display The display context object
Close the connection to display and free all resources associated with it.
int wl_display_dispatch (struct wl_display * display)
Process incoming events
Parameters
display The display context object
Returns
The number of dispatched events on success or -1 on failure
Dispatch events on the default event queue.
If the default event queue is empty, this function blocks until there are events to be
read from the display fd. Events are read and queued on the appropriate event queues.
Finally, events on the default event queue are dispatched. On failure -1 is returned and
errno set appropriately.
In a multi threaded environment, do not manually wait using poll() (or equivalent) before
calling this function, as doing so might cause a dead lock. If external reliance on poll()
(or equivalent) is required, see wl_display_prepare_read_queue() of how to do so.
This function is thread safe as long as it dispatches the right queue on the right thread.
It is also compatible with the multi thread event reading preparation API (see
wl_display_prepare_read_queue()), and uses the equivalent functionality internally. It is
not allowed to call this function while the thread is being prepared for reading events,
and doing so will cause a dead lock.
Note
It is not possible to check if there are events on the queue or not. For dispatching
default queue events without blocking, see wl_display_dispatch_pending().
See also
wl_display_dispatch_pending(), wl_display_dispatch_queue(), wl_display_read_events()
int wl_display_dispatch_pending (struct wl_display * display)
Dispatch default queue events without reading from the display fd
Parameters
display The display context object
Returns
The number of dispatched events or -1 on failure
This function dispatches events on the main event queue. It does not attempt to read the
display fd and simply returns zero if the main queue is empty, i.e., it doesn't block.
See also
wl_display_dispatch(), wl_display_dispatch_queue(), wl_display_flush()
int wl_display_dispatch_queue (struct wl_display * display, struct wl_event_queue * queue)
Dispatch events in an event queue
Parameters
display The display context object
queue The event queue to dispatch
Returns
The number of dispatched events on success or -1 on failure
Dispatch events on the given event queue.
If the given event queue is empty, this function blocks until there are events to be read
from the display fd. Events are read and queued on the appropriate event queues. Finally,
events on given event queue are dispatched. On failure -1 is returned and errno set
appropriately.
In a multi threaded environment, do not manually wait using poll() (or equivalent) before
calling this function, as doing so might cause a dead lock. If external reliance on poll()
(or equivalent) is required, see wl_display_prepare_read_queue() of how to do so.
This function is thread safe as long as it dispatches the right queue on the right thread.
It is also compatible with the multi thread event reading preparation API (see
wl_display_prepare_read_queue()), and uses the equivalent functionality internally. It is
not allowed to call this function while the thread is being prepared for reading events,
and doing so will cause a dead lock.
It can be used as a helper function to ease the procedure of reading and dispatching
events.
Note
Since Wayland 1.5 the display has an extra queue for its own events (i. e. delete_id).
This queue is dispatched always, no matter what queue we passed as an argument to this
function. That means that this function can return non-0 value even when it haven't
dispatched any event for the given queue.
See also
wl_display_dispatch(), wl_display_dispatch_pending(),
wl_display_dispatch_queue_pending(), wl_display_prepare_read_queue()
int wl_display_dispatch_queue_pending (struct wl_display * display, struct wl_event_queue *
queue)
Dispatch pending events in an event queue
Parameters
display The display context object
queue The event queue to dispatch
Returns
The number of dispatched events on success or -1 on failure
Dispatch all incoming events for objects assigned to the given event queue. On failure -1
is returned and errno set appropriately. If there are no events queued, this function
returns immediately.
Since
1.0.2
int wl_display_flush (struct wl_display * display)
Send all buffered requests on the display to the server
Parameters
display The display context object
Returns
The number of bytes sent on success or -1 on failure
Send all buffered data on the client side to the server. Clients should always call this
function before blocking on input from the display fd. On success, the number of bytes
sent to the server is returned. On failure, this function returns -1 and errno is set
appropriately.
wl_display_flush() never blocks. It will write as much data as possible, but if all data
could not be written, errno will be set to EAGAIN and -1 returned. In that case, use poll
on the display file descriptor to wait for it to become writable again.
struct wl_list * wl_display_get_client_list (struct wl_display * display)
Get the list of currently connected clients
Parameters
display The display object
This function returns a pointer to the list of clients currently connected to the display.
You can iterate on the list by using the wl_client_for_each macro. The returned value is
valid for the lifetime of the display. You must not modify the returned list, but only
access it.
See also
wl_client_for_each()
wl_client_get_link()
wl_client_from_link()
int wl_display_get_error (struct wl_display * display)
Retrieve the last error that occurred on a display
Parameters
display The display context object
Returns
The last error that occurred on display or 0 if no error occurred
Return the last error that occurred on the display. This may be an error sent by the
server or caused by the local client.
Note
Errors are fatal. If this function returns non-zero the display can no longer be used.
int wl_display_get_fd (struct wl_display * display)
Get a display context's file descriptor
Parameters
display The display context object
Returns
Display object file descriptor
Return the file descriptor associated with a display so it can be integrated into the
client's main loop.
uint32_t wl_display_get_protocol_error (struct wl_display * display, const struct wl_interface
** interface, uint32_t * id)
Retrieves the information about a protocol error:
Parameters
display The Wayland display
interface if not NULL, stores the interface where the error occurred, or NULL, if
unknown.
id if not NULL, stores the object id that generated the error, or 0, if the object id
is unknown. There's no guarantee the object is still valid; the client must know if it
deleted the object.
Returns
The error code as defined in the interface specification.
int err = wl_display_get_error(display);
if (err == EPROTO) {
code = wl_display_get_protocol_error(display, &interface, &id);
handle_error(code, interface, id);
}
...
uint32_t wl_display_get_serial (struct wl_display * display)
Get the current serial number
Parameters
display The display object
This function returns the most recent serial number, but does not increment it.
uint32_t wl_display_next_serial (struct wl_display * display)
Get the next serial number
Parameters
display The display object
This function increments the display serial number and returns the new value.
int wl_display_prepare_read (struct wl_display * display)
Prepare to read events from the display's file descriptor
Parameters
display The display context object
Returns
0 on success or -1 if event queue was not empty
This function does the same thing as wl_display_prepare_read_queue() with the default
queue passed as the queue.
See also
wl_display_prepare_read_queue
int wl_display_prepare_read_queue (struct wl_display * display, struct wl_event_queue * queue)
Prepare to read events from the display's file descriptor to a queue
Parameters
display The display context object
queue The event queue to use
Returns
0 on success or -1 if event queue was not empty
This function (or wl_display_prepare_read()) must be called before reading from the file
descriptor using wl_display_read_events(). Calling wl_display_prepare_read_queue()
announces the calling thread's intention to read and ensures that until the thread is
ready to read and calls wl_display_read_events(), no other thread will read from the file
descriptor. This only succeeds if the event queue is empty, and if not -1 is returned and
errno set to EAGAIN.
If a thread successfully calls wl_display_prepare_read_queue(), it must either call
wl_display_read_events() when it's ready or cancel the read intention by calling
wl_display_cancel_read().
Use this function before polling on the display fd or integrate the fd into a toolkit
event loop in a race-free way. A correct usage would be (with most error checking left
out):
while (wl_display_prepare_read_queue(display, queue) != 0)
wl_display_dispatch_queue_pending(display, queue);
wl_display_flush(display);
ret = poll(fds, nfds, -1);
if (has_error(ret))
wl_display_cancel_read(display);
else
wl_display_read_events(display);
wl_display_dispatch_queue_pending(display, queue);
Here we call wl_display_prepare_read_queue(), which ensures that between returning from
that call and eventually calling wl_display_read_events(), no other thread will read from
the fd and queue events in our queue. If the call to wl_display_prepare_read_queue()
fails, we dispatch the pending events and try again until we're successful.
The wl_display_prepare_read_queue() function doesn't acquire exclusive access to the
display's fd. It only registers that the thread calling this function has intention to
read from fd. When all registered readers call wl_display_read_events(), only one (at
random) eventually reads and queues the events and the others are sleeping meanwhile. This
way we avoid races and still can read from more threads.
See also
wl_display_cancel_read(), wl_display_read_events(), wl_display_prepare_read()
int wl_display_read_events (struct wl_display * display)
Read events from display file descriptor
Parameters
display The display context object
Returns
0 on success or -1 on error. In case of error errno will be set accordingly
Calling this function will result in data available on the display file descriptor being
read and read events will be queued on their corresponding event queues.
Before calling this function, depending on what thread it is to be called from,
wl_display_prepare_read_queue() or wl_display_prepare_read() needs to be called. See
wl_display_prepare_read_queue() for more details.
When being called at a point where other threads have been prepared to read (using
wl_display_prepare_read_queue() or wl_display_prepare_read()) this function will sleep
until all other prepared threads have either been cancelled (using
wl_display_cancel_read()) or them self entered this function. The last thread that calls
this function will then read and queue events on their corresponding event queues, and
finally wake up all other wl_display_read_events() calls causing them to return.
If a thread cancels a read preparation when all other threads that have prepared to read
has either called wl_display_cancel_read() or wl_display_read_events(), all reader threads
will return without having read any data.
To dispatch events that may have been queued, call wl_display_dispatch_pending() or
wl_display_dispatch_queue_pending().
See also
wl_display_prepare_read(), wl_display_cancel_read(), wl_display_dispatch_pending(),
wl_display_dispatch()
int wl_display_roundtrip (struct wl_display * display)
Block until all pending request are processed by the server
Parameters
display The display context object
Returns
The number of dispatched events on success or -1 on failure
This function blocks until the server has processed all currently issued requests by
sending a request to the display server and waiting for a reply before returning.
This function uses wl_display_dispatch_queue() internally. It is not allowed to call this
function while the thread is being prepared for reading events, and doing so will cause a
dead lock.
Note
This function may dispatch other events being received on the default queue.
int wl_display_roundtrip_queue (struct wl_display * display, struct wl_event_queue * queue)
Block until all pending request are processed by the server
Parameters
display The display context object
queue The queue on which to run the roundtrip
Returns
The number of dispatched events on success or -1 on failure
This function blocks until the server has processed all currently issued requests by
sending a request to the display server and waiting for a reply before returning.
This function uses wl_display_dispatch_queue() internally. It is not allowed to call this
function while the thread is being prepared for reading events, and doing so will cause a
dead lock.
Note
This function may dispatch other events being received on the given queue.
See also
wl_display_roundtrip()
void wl_display_set_global_filter (struct wl_display * display,
wl_display_global_filter_func_t filter, void * data)
Set a filter function for global objects
Parameters
display The Wayland display object.
filter The global filter function.
data User data to be associated with the global filter.
Returns
None.
Set a filter for the wl_display to advertise or hide global objects to clients. The set
filter will be used during wl_global advertisement to determine whether a global object
should be advertised to a given client, and during wl_global binding to determine whether
a given client should be allowed to bind to a global.
Clients that try to bind to a global that was filtered out will have an error raised.
Setting the filter NULL will result in all globals being advertised to all clients. The
default is no filter.
The filter should be installed before any client connects and should always take the same
decision given a client and a global. Not doing so will result in inconsistent filtering
and broken wl_registry event sequences.
Field Documentation
struct wl_array wl_display::additional_shm_formats struct wl_list wl_display::client_list struct wl_priv_signal wl_display::create_client_signal struct wl_priv_signal wl_display::destroy_signal wl_display_global_filter_func_t wl_display::global_filter void* wl_display::global_filter_data struct wl_list wl_display::global_list uint32_t wl_display::id struct wl_event_loop* wl_display::loop struct wl_list wl_display::protocol_loggers struct wl_list wl_display::registry_resource_list int wl_display::run uint32_t wl_display::serial struct wl_list wl_display::socket_list struct wl_event_source* wl_display::term_source int wl_display::terminate_efd
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