private boolean casProducerIndex(final long expected, long update) {
        return UNSAFE.compareAndSwapLong(null, producerIndexAddress, expected, update);
    }
This is to be used for an IPC queue with the direct buffer used being a memory mapped file.

@param buff
@param capacity
jctools-channels/src/main/java/org/jctools/channels/mpsc/MpscOffHeapFixedSizeRingBuffer.java