14 Dec
2011
14 Dec
'11
4:33 a.m.
On Tue, Dec 13, 2011 at 10:02 PM, Iain Duncan <iainduncanlists(a)gmail.com> wrote:
Thanks Paul. I'm working in C++, but I'm using
the jack C api, which from
the docs I see has a signature for
size_t jack_ringbuffer_write ( jack_ringbuffer_t * rb, const char * src,
size_t cnt )
My DataMessage structure is just a simple C structure for now. Is there a
recommended way of writing it to the ringbuffer given that I want to do
something like this:
void MessageQueue::push( DataMessage msg ){
// write to the ring buffer, converting DataMessage to a string
unsigned int written = jack_ringbuffer_write( mRingBuffer, (char *) &msg
, sizeof(DataMessage) );
// etc
}
as long as the struct is POD (Plain Old Data - no embedded pointers,
etc), this will work fine.
however, you need to keep in mind that under some easily encounterable
circumstances, the write may not return sizeof(DataMessage). this is a
very easy mistake to make with ringbuffers (ditto for read).
it can be avoided via careful sizing of the ringbuffer and always
read/writing "whole objects" OR by carefully checking the results of
read/write.
the jack ringbuffer design is particular bad in this respect because
it can only hold size-1 bytes (where size is its actual size).
ardour has some slightly better behaved, templated ringbuffers for this purpose.