Description of problem:

Calling Session::nextReceiver() with a duration of IMMEDIATE will always return null, even if there are incoming messages waiting. This bug was introduced as part of the fix for bug 958895.

Version-Release number of selected component (if applicable):

qpid-0.24, mrg 2.3.3, qpid-0.28

How reproducible:

Easily

Steps to Reproduce:
1. put some messages in a queue
2. have a program that creates a receiver for the queue, sets a non-zero capacity, then loops until nextReceiver(Duration::IMMEDIATE returns a non-null receiver), e.g.:

   ssn.createReceiver("my-queue").setCapacity(1);
   Receiver next;
   while (ssn.nextReceiver(Duration::IMMEDIATE)) {}
   next.get(Duration::IMMEDIATE)


Actual results:

The while loop never returns, even though there are messages on the queue

Expected results:

The while loop exits once the broker has sent out (a) message(s)

Additional info:

It should be pointed out that using nextReceiver() with a Duration::IMMEDIATE value in this way is inefficient and rather odd. A much better solution would be to specify some non-zero timeout. This would avoid the cpu usage of a 'busy wait' while in no way either increasing the actual time until the next receiver is obtained or the maximum theoretical time.

Using nextReceiver() with a non-zero timeout also avoids this bug.