Circular buffer implementation in C

I have found pseudo code on how to implem开发者_C百科ent a circular buffer.

// Producer.
while (true) {
  /* produce item v */
  while ((in+1)%n == out)
    /* Wait. */;
  b[in] = v;
  in = (in + 1) % n
}

// Consumer.
while (true) {
  while (in == out)
    /* Wait. */;
  w = b[out];
  out = (out + 1) % n;
  /* Consume item w. */
}

What I don't understand is the "Consume item w." comment, because I think that with w = b[out]; we are consuming w, aren't we?

With

w = b[out];

You only grab a copy of the item to be consumed. With

out = (out + 1) % n;

You advance the index of the item to be consumed, thereby preventing it from being referenced again.

In a manner, multiple calls to w = b[out]; don't actually consume the buffer's slot, it just accesses it; while out = (out + 1) % n; prevents further access of that item. Preventing further access of the buffer item is the strongest definition of the term "consume the item" that I can think of.

these two lines are both part of consuming process:

w = b[out];
out = (out + 1) % n;

The first extract the value and the second increment the out index. The comment refers to the previously two lines.

Yes, because then it's out of the buffer, which the following row says is empty. Then we can process w.