[LAD] jack ringbuffer question

[lieven moors]

Paul Davis wrote:
> On Tue, Dec 1, 2009 at 9:22 PM, lieven moors <lievenmoors at gmail.com> wrote:
>
>   
>> if( (jack_ringbuffer_read_space( (*arps_jack)[i].rb ) ) ==
>>        (sizeof( Arp ) * 2) )
>> {
>>   jack_ringbuffer_read_advance( (*arps_jack)[i].rb, sizeof(Arp) ) ;
>> }
>>     
>
> You've just moved the read ptrs, before reading any data. Why did you
> check to see if there were 2 Arp structures available, and then skip
> one of them?
>
>   
>> if( (jack_ringbuffer_read_space( (*arps_jack)[i].rb ) ) ==
>>        sizeof( Arp ) )
>>     
>
> this won't return true unless there ONLY one Arp struct to read.
>
>   
>> {
>>   jack_ringbuffer_data_t data[2] ;
>>   jack_ringbuffer_get_read_vector( (*arps_jack)[i].rb, data ) ;
>>     
>
> now you've got a read vector, but *after* you advanced the read ptr.
>
>   
>>   if ( data[0].len > 0 )
>>   {
>>    arp = reinterpret_cast<Arp*>( data[0].buf ) ;
>>    steps = &arp->steps ;
>>    scale = &arp->scale ;
>>   }
>>   else if( data[1].len > 0)
>>   {
>>    cout << "data in second part of ringbuffer, this should not
>>        happen!" <<  endl ;
>>   }
>>     
>
> now you've used the data from the ringbuffer, but not advanced the read ptr.
> if you're going to use get_read_vector() you want to do that first,
> then explicitly advanced the read ptr.
>
> not sure if this is all that is going wrong, but this looks odd/wrong
> to me as a starting point.
>
>   
I want to repeat the same Arp, until there is an update to the text 
file. One arp is allready
loaded in each ringbuffer in main(). When the file is modified, a second 
one is added, and
process skips to the second one. Since I have only space for two arps in 
the buffer, there
should always be exactly one which is readable. I know it is a bit 
weird, but it seems to
work, apart from the problem I described.