wl_event_source(3)

NAME
wl_event_source - An abstract event source.

SYNOPSIS

#include <wayland-server-core.h>

  Public Types
typedef int(* wl_event_loop_fd_func_t) (int fd, uint32_t mask, void *data)
typedef int(* wl_event_loop_timer_func_t) (void *data)
typedef int(* wl_event_loop_signal_func_t) (int signal_number, void *data)
typedef void(* wl_event_loop_idle_func_t) (void *data)

  Public Member Functions
struct wl_event_source * wl_event_loop_add_fd (struct wl_event_loop *loop, int fd, uint32_t mask, wl_event_loop_fd_func_t func, void *data)
int wl_event_source_fd_update (struct wl_event_source *source, uint32_t mask)
struct wl_event_source * wl_event_loop_add_timer (struct wl_event_loop *loop, wl_event_loop_timer_func_t func, void *data)
int wl_event_source_timer_update (struct wl_event_source *source, int ms_delay)
struct wl_event_source * wl_event_loop_add_signal (struct wl_event_loop *loop, int signal_number, wl_event_loop_signal_func_t func, void *data)
struct wl_event_source * wl_event_loop_add_idle (struct wl_event_loop *loop, wl_event_loop_idle_func_t func, void *data)
void wl_event_source_check (struct wl_event_source *source)
int wl_event_source_remove (struct wl_event_source *source)

Detailed Description

An abstract event source. This is the generic type for fd, timer, signal, and idle sources. Functions that operate on specific source types must not be used with a different type, even if the function signature allows it.

Member Typedef Documentation

  typedef int(* wl_event_loop_fd_func_t) (int fd, uint32_t mask, void *data)
File descriptor dispatch function type

Functions of this type are used as callbacks for file descriptor events.

Parameters
    fd The file descriptor delivering the event.
    mask Describes the kind of the event as a bitwise-or of: WL_EVENT_READABLE, WL_EVENT_WRITABLE, WL_EVENT_HANGUP, WL_EVENT_ERROR.
    data The user data argument of the related wl_event_loop_add_fd() call.

Returns
    If the event source is registered for re-check with wl_event_source_check(): 0 for all done, 1 for needing a re-check. If not registered, the return value is ignored and should be zero.

See also
    wl_event_loop_add_fd()

  typedef void(* wl_event_loop_idle_func_t) (void *data)
Idle task function type

Functions of this type are used as callbacks before blocking in wl_event_loop_dispatch().

Parameters
    data The user data argument of the related wl_event_loop_add_idle() call.

See also
    wl_event_loop_add_idle() wl_event_loop_dispatch()

  typedef int(* wl_event_loop_signal_func_t) (int signal_number, void *data)
Signal dispatch function type

Functions of this type are used as callbacks for (POSIX) signals.

Parameters
    signal_number
    data The user data argument of the related wl_event_loop_add_signal() call.

Returns
    If the event source is registered for re-check with wl_event_source_check(): 0 for all done, 1 for needing a re-check. If not registered, the return value is ignored and should be zero.

See also
    wl_event_loop_add_signal()

  typedef int(* wl_event_loop_timer_func_t) (void *data)
Timer dispatch function type

Functions of this type are used as callbacks for timer expiry.

Parameters
    data The user data argument of the related wl_event_loop_add_timer() call.

Returns
    If the event source is registered for re-check with wl_event_source_check(): 0 for all done, 1 for needing a re-check. If not registered, the return value is ignored and should be zero.

See also
    wl_event_loop_add_timer()

Member Function Documentation

  struct wl_event_source * wl_event_loop_add_fd (struct wl_event_loop * loop, int fd, uint32_t mask, wl_event_loop_fd_func_t func, void * data)
Create a file descriptor event source

Parameters
    loop The event loop that will process the new source.
    fd The file descriptor to watch.
    mask A bitwise-or of which events to watch for: WL_EVENT_READABLE, WL_EVENT_WRITABLE.
    func The file descriptor dispatch function.
    data User data.

Returns
    A new file descriptor event source.

The given file descriptor is initially watched for the events given in mask. This can be changed as needed with wl_event_source_fd_update().

If it is possible that program execution causes the file descriptor to be read while leaving the data in a buffer without actually processing it, it may be necessary to register the file descriptor source to be re-checked, see wl_event_source_check(). This will ensure that the dispatch function gets called even if the file descriptor is not readable or writable anymore. This is especially useful with IPC libraries that automatically buffer incoming data, possibly as a side-effect of other operations.

See also
    wl_event_loop_fd_func_t

  struct wl_event_source * wl_event_loop_add_idle (struct wl_event_loop * loop, wl_event_loop_idle_func_t func, void * data)
Create an idle task

Parameters
    loop The event loop that will process the new task.
    func The idle task dispatch function.
    data User data.

Returns
    A new idle task (an event source).

Idle tasks are dispatched before wl_event_loop_dispatch() goes to sleep. See wl_event_loop_dispatch() for more details.

Idle tasks fire once, and are automatically destroyed right after the callback function has been called.

An idle task can be cancelled before the callback has been called by wl_event_source_remove(). Calling wl_event_source_remove() after or from within the callback results in undefined behaviour.

See also
    wl_event_loop_idle_func_t

  struct wl_event_source * wl_event_loop_add_signal (struct wl_event_loop * loop, int signal_number, wl_event_loop_signal_func_t func, void * data)
Create a POSIX signal event source

Parameters
    loop The event loop that will process the new source.
    signal_number Number of the signal to watch for.
    func The signal dispatch function.
    data User data.

Returns
    A new signal event source.

This function blocks the normal delivery of the given signal in the calling thread, and creates a 'watch' for it. Signal delivery no longer happens asynchronously, but by wl_event_loop_dispatch() calling the dispatch callback function func.

It is the caller's responsibility to ensure that all other threads have also blocked the signal.

See also
    wl_event_loop_signal_func_t

  struct wl_event_source * wl_event_loop_add_timer (struct wl_event_loop * loop, wl_event_loop_timer_func_t func, void * data)
Create a timer event source

Parameters
    loop The event loop that will process the new source.
    func The timer dispatch function.
    data User data.

Returns
    A new timer event source.

The timer is initially disarmed. It needs to be armed with a call to wl_event_source_timer_update() before it can trigger a dispatch call.

See also
    wl_event_loop_timer_func_t

  void wl_event_source_check (struct wl_event_source * source)
Mark event source to be re-checked

Parameters
    source The event source to be re-checked.

This function permanently marks the event source to be re-checked after the normal dispatch of sources in wl_event_loop_dispatch(). Re-checking will keep iterating over all such event sources until the dispatch function for them all returns zero.

Re-checking is used on sources that may become ready to dispatch as a side-effect of dispatching themselves or other event sources, including idle sources. Re-checking ensures all the incoming events have been fully drained before wl_event_loop_dispatch() returns.

  int wl_event_source_fd_update (struct wl_event_source * source, uint32_t mask)
Update a file descriptor source's event mask

Parameters
    source The file descriptor event source to update.
    mask The new mask, a bitwise-or of: WL_EVENT_READABLE, WL_EVENT_WRITABLE.

Returns
    0 on success, -1 on failure.

This changes which events, readable and/or writable, cause the dispatch callback to be called on.

File descriptors are usually writable to begin with, so they do not need to be polled for writable until a write actually fails. When a write fails, the event mask can be changed to poll for readable and writable, delivering a dispatch callback when it is possible to write more. Once all data has been written, the mask can be changed to poll only for readable to avoid busy-looping on dispatch.

See also
    wl_event_loop_add_fd()

  int wl_event_source_remove (struct wl_event_source * source)
Remove an event source from its event loop

Parameters
    source The event source to be removed.

Returns
    Zero.

The event source is removed from the event loop it was created for, and is effectively destroyed. This invalidates source . The dispatch function of the source will no longer be called through this source.

  int wl_event_source_timer_update (struct wl_event_source * source, int ms_delay)
Arm or disarm a timer

Parameters
    source The timer event source to modify.
    ms_delay The timeout in milliseconds.

Returns
    0 on success, -1 on failure.

If the timeout is zero, the timer is disarmed.

If the timeout is non-zero, the timer is set to expire after the given timeout in milliseconds. When the timer expires, the dispatch function set with wl_event_loop_add_timer() is called once from wl_event_loop_dispatch(). If another dispatch is desired after another expiry, wl_event_source_timer_update() needs to be called again.

Author

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