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Read pending control events
#include <sys/asoundlib.h>
int snd_ctl_read( snd_ctl_t *handle,
snd_ctl_callbacks_t *callbacks );
- handle
- The handle for the control connection to the card.
This must be a handle created by
snd_ctl_open().
- callbacks
- A pointer to a
snd_ctl_callbacks_t
structure that defines the callbacks for the events.
libasound.so
The snd_ctl_read() function
reads pending control events from the control handle.
As each event is read, the list of callbacks is checked for a handler for this event.
If a match is found, the callback is invoked.
This function is usually called on the return of the
select()
library call (see the QNX Library Reference).
|
If you register to receive notification of events (e.g. by using
select()), it's very important that you clear the event queue
by calling snd_ctl_read(), even if you don't want or need the
information.
The event queues are open-ended and may cause trouble if allowed to grow
in an uncontrolled manner.
The best practice is to read the events in the queues as you receive
notification, so that they don't have a chance to accumulate. |
The number of events read from the handle, or a negative value on error.
- -EBADF
- Invalid file descriptor. Your handle may be corrupt.
- -EINTR
- The read operation was interrupted by a signal, and either no data was
transferred, or the resource manager responsible for that file doesn't
report partial transfers.
- -EIO
- An event I/O error occurred.
QNX Neutrino
Safety: | |
Cancellation point |
No |
Interrupt handler |
No |
Signal handler |
Yes |
Thread |
Yes |
snd_ctl_callbacks_t,
snd_ctl_file_descriptor(),
snd_ctl_open()
select()
in the QNX Library Reference
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