libvc | Vulkan Compute for C | GPU library

I think your get_samples thread generates audio faster or slower than streamCallback consumes them. Using clock for flow control is unreliable.

Simple way to fix, remove that thread and sample_buffer queue and generate samples directly in streamCallback function.

If you do want to use multithreading for your app, it requires proper synchronization between producer and consumer. Much more complex. But in short, the steps are below.

1. Replace your queue with a reasonably small fixed-length circular buffer. Technically, std::queue will work too, just slower because pointer-based, and you need to manually limit the max.size.

2. In producer thread implement endless loop that checks is there empty space in the buffer, if there’s space generate more audio, if not, wait for the consumer to consume the data from the buffer.

3. In consumer streamCallback callback, copy data from circular buffer to output_buf. If there’s not enough data available, wake the producer thread and wait for it to produce the data.

Unfortunately an efficient implementation of that is quite tricky. You need synchronization to protect shared data, but you don’t want too much synchronization otherwise producer and consumer will be serialized and will only use a single hardware thread. One approach is single std::mutex to protect the buffer while moving pointers/size/ofset (but unlock while reading/writing the data), and two std::condition_variable, one for the producer to sleep when there’s no free space in the buffer, another one for the consumer to sleep when there’s no data in the buffer.