[LAD] Realtime threads and security

[Robin Gareus]

On 02/24/2011 03:59 PM, Olivier Guilyardi wrote:
> Hello Robin,
> 
> Now, say I'm only focusing on playback now. Is there something wrong with
> calling a blocking output API from a realtime thread as I ask below?
>

mmh. it depends on how the blocking is done. If it is a spin-lock it
will consume CPU and block other processes which are running at lower
priority in the meantime (but only up to sched_rt_runtime_us per second.
Other processes won't starve). Is there a poll (or select) function
available as part of the libaudio API?

If the i/o block waits for a signal (e.g. IRQ), it will work just fine.

>>> On Android, the closest that one can get to hardware in a more or less portable
>>> way is libaudio [1]. It's Android's audio HAL. This API exposes blocking read()
>>> and write() calls, with fixed buffer sizes (input and output buffer sizes
>>> generally do not match, but that's another problem).
>>>
>>> So, this may be a silly/newbie question, but can one access this blocking API
>>> from a realtime thread? What will happen when it blocks? How does the read/write
>>> period relate to sched_rt_period_us?
>>>
>>> [1] http://source.android.com/porting/audio.html
> 
> --
>   Olivier