Re: [LAD] segfaulting using my ringbuffer queue, stuck!

Found the problem, of course, bad pointer handling. But any feeback on how
my code looks would still be welcome.

Thanks
Iain

On Fri, Dec 30, 2011 at 11:16 AM, Iain Duncan <iainduncanlists@email-addr-hiddenwrote:

> Hi folks, wondering if anyone might be able to point me at the way to sort
> this out, my latest queue is segfaulting when written to or read from,
> while the rest ( which are supposed to be identical except for message type
> ) are working great, and have been tested with full stack runs fine. I'm
> banging my head on the desk at this point trying to find the difference,
> but perhaps others have seen similar behaviour?
>
> I've made a template class for a queue, that internally uses a jack
> ringbuffer. I have four of them, some of my data message struct, one for a
> csound note message struct, and a new one for my raw midi message struct
> which looks this this:
>
> struct MidiMessage {
> char status;
> char data_1;
> char data_2;
> int time; // time in samples when midi message arrived
> };
>
> I instantiate them before anything else and pass them into the components
> that need them in their constructors
>
> MessageQueue<DataMessage> *toEngineDataQueue = new
> MessageQueue<DataMessage>();
> MessageQueue<DataMessage> *fromEngineDataQueue = new
> MessageQueue<DataMessage>();
> MessageQueue<NoteMessage> *toEngineNoteQueue = new
> MessageQueue<NoteMessage>();
> MessageQueue<MidiMessage> *fromEngineMidiQueue = new
> MessageQueue<MidiMessage>();
>
> All instantiation is working fine, app starts up, and the first three
> queues are working. As soon as I either write to or read from the midi
> queue, I segfault. Not sure how to debug this, hints welcome! Below is the
> cue code in case anyone wants to look at it. I can't see anything wrong,
> but maybe I've been doing something wrong and just gotten lucky so far??
>
> thanks
> Iain
>
> template <class Type>
> class MessageQueue {
>
> private:
> // pointer to the ring buffer the ring buffer
> jack_ringbuffer_t *mRingBuffer;
> int mQueueLength;
>
> public:
> MessageQueue();
> ~MessageQueue();
>
> // put a msg on the queue, returns 0 or error code
> void push( Type msg );
> // store message in msg, returns true if message
> bool tryPop( Type *msg );
> };
>
> template <class Type>
> MessageQueue<Type>::MessageQueue(){
>
> mQueueLength = DEFAULT_QUEUE_LENGTH;
> // create our ringbuffer, sized by Type
> mRingBuffer = jack_ringbuffer_create( mQueueLength * sizeof(Type) );
>
> // lock the buffer into memory, this is *NOT* realtime safe
> int errorLocking = jack_ringbuffer_mlock(mRingBuffer);
> if( errorLocking ){
> std::cout << "MessageQueue - Error locking memory when creating
> ringbuffer\n";
> // XXX raise an exception or something?? how do we fail here??
> }
>
> }
>
> template <class Type>
> MessageQueue<Type>::~MessageQueue(){
> cout << "MessageQueue destructor\n";
> // free the memory allocated for the ring buffer
> ack_ringbuffer_free( mRingBuffer );
> }
>
> template <class Type>
> void MessageQueue<Type>::push( Type msg ){
> // write to the ring buffer, converting Type to a string
> unsigned int written = jack_ringbuffer_write( mRingBuffer, (const char
> *) &msg , sizeof(Type) );
>
> // XXX: what to do if it fails anyway??
> if( written < sizeof(Type) ){
> cout << "Error, unable to write full message to ring buffer\n";
> // do something else here yo!
> }
> }
>
> // if a message is on the queue, get it
> // returns True if it got a message
> template <class Type>
> bool MessageQueue<Type>::tryPop( Type *msgBuf ){
>
> // if there is a message on the ring buffer, copy contents into msg
> if( jack_ringbuffer_read_space( mRingBuffer) >= sizeof(Type) ){
> jack_ringbuffer_read( mRingBuffer, (char *)msgBuf, sizeof(Type) );
> // return True because a msg was read
> return 1;
> }else{
> // return False, no msg read
> return 0;
> }
> }
>
>

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Received on Sat Dec 31 00:15:03 2011