Number of messages in 'unbounded_buffer'

Question

The class Concurrency::unbounded_buffer can store any number of messages. But how to know number of pending (not received) messages?

Answer 1

There's no functionality built in to do this.

What you can do is atomically increment/decrement an integer alongside it, but know that this won't be a reliable count (only a ballpark) if it's being accessed concurrently.

long count;
Concurrency::unbounded_buffer<T> buffer;

if(Concurrency::send(buffer, T()))
{
    long new_count = _InterlockedIncrement(&count);
}

And elsewhere:

T value = Concurrency::receive(buffer);
long new_count = _InterlockedDecrement(&count);

You'll find the _Interlocked functions in <intrin.h>.