[9fans] OT: cannonical set of queue ops

["Steve Simon" <steve@quintile.net>]

Hi,

Bit off topic

In an embedded system, we are trying to wrap up the specifics
of the RTOS we use and abstract it a little so we can switch
OS later (to a cheaper one :-)

We are therefore trying to come to a cannonical API, the only
part of this we are having problems are interlocked queues.

These are queues which the reader blocks if they are empty and
the writer blocks if full. They have an option for a timeout
which can be -1 to indicate forever or 0 for poll.

We have found a need for a either IsQueueEmpty() or PeekQueueHead()
entrypoint - a network driver is closing a connection a cleanup thread
needs to poll the queue so it can deallocate it once all the remaining data
has drained; we cannot just read the queue to see if its empty as this will
remove the head entry if there is one.

This is the one and only place we seem to need this so we are worried.

Are we suffering from a lack of vision, or is some way of checking the
number of items on a queue inevitable?

-Steve