async.c File Reference

Async notification helpers. More...

Functions
int	snd_async_add_handler (snd_async_handler_t **handler, int fd, snd_async_callback_t callback, void *private_data)
	Registers an async handler.
int	snd_async_del_handler (snd_async_handler_t *handler)
	Deletes an async handler.
int	snd_async_handler_get_signo (snd_async_handler_t *handler)
	Returns the signal number assigned to an async handler.
int	snd_async_handler_get_fd (snd_async_handler_t *handler)
	Returns the file descriptor assigned to an async handler.
void *	snd_async_handler_get_callback_private (snd_async_handler_t *handler)
	Returns the private data assigned to an async handler.

Detailed Description

Async notification helpers.

Author

Abramo Bagnara abram.nosp@m.o@al.nosp@m.sa-pr.nosp@m.ojec.nosp@m.t.org

Date

2001

Function Documentation

snd_async_add_handler()

int snd_async_add_handler	(	snd_async_handler_t **	handler,
		int	fd,
		snd_async_callback_t	callback,
		void *	private_data )

Registers an async handler.

Parameters

handler	The function puts the pointer to the new async handler object at the address specified by handler.
fd	The file descriptor to be associated with the callback.
callback	The async callback function.
private_data	Private data for the async callback function.

Returns

Zero if successful, otherwise a negative error code.

This function associates the callback function with the given file, and saves this association in a snd_async_handler_t object.

Whenever the SIGIO signal is raised for the file fd, the callback function will be called with its parameter pointing to the async handler object returned by this function.

The ALSA sigaction handler for the SIGIO signal automatically multiplexes the notifications to the registered async callbacks. However, the application is responsible for instructing the device driver to generate the SIGIO signal.

The SIGIO signal may have been replaced with another signal, see snd_async_handler_get_signo.

When the async handler isn't needed anymore, you must delete it with snd_async_del_handler.

See also

snd_async_add_pcm_handler, snd_async_add_ctl_handler

snd_async_del_handler()

int snd_async_del_handler

(

snd_async_handler_t *

handler

)

Deletes an async handler.

Parameters

handler

Handle of the async handler to delete.

Returns

Zero if successful, otherwise a negative error code.

snd_async_handler_get_callback_private()

void * snd_async_handler_get_callback_private

(

snd_async_handler_t *

handler

)

Returns the private data assigned to an async handler.

Parameters

handler

Handle to an async handler.

Returns

The private_data value registered with the async handler.

Examples

/test/pcm.c, and /test/timer.c.

snd_async_handler_get_fd()

int snd_async_handler_get_fd

(

snd_async_handler_t *

handler

)

Returns the file descriptor assigned to an async handler.

Parameters

handler

Handle to an async handler.

Returns

The file descriptor if successful, otherwise a negative error code.

snd_async_handler_get_signo()

int snd_async_handler_get_signo

(

snd_async_handler_t *

handler

)

Returns the signal number assigned to an async handler.

Parameters

handler

Handle to an async handler.

Returns

The signal number if successful, otherwise a negative error code.

The signal number for async handlers usually is SIGIO, but wizards can redefine it to a realtime signal when compiling the ALSA library.