Provided by: libwayland-doc_1.16.0-1ubuntu1.1~18.04.4_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
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.
The Unix socket will be created in the directory pointed to by environment variable XDG_RUNTIME_DIR. If
XDG_RUNTIME_DIR is not set, then this function fails and returns -1.
The length of socket path, i.e., the path set in XDG_RUNTIME_DIR and the socket name, must not exceed the
maximum length of a Unix socket path. The function also fails if the user do not have write permission in
the XDG_RUNTIME_DIR path or if the socket name 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 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 funtion.
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 advertisment 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.
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
Author
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