/**
* Remove the channel from the channel map and free the number for re-use. This method must be
* safe to call multiple times on the same channel. If it is not then things go badly wrong.
*/
public void releaseChannelNumber(ChannelN channel) {
// Warning, here be dragons. Not great big ones, but little baby ones
// which will nibble on your toes and occasionally trip you up when
// you least expect it. (Pixies? HP2)
// Basically, there's a race that can end us up here. It almost never
// happens, but it's easier to repair it when it does than prevent it
// from happening in the first place.
// If we end up doing a Channel.close in one thread and a Channel.open
// with the same channel number in another, the two can overlap in such
// a way as to cause disconnectChannel on the old channel to try to
// remove the new one. Ideally we would fix this race at the source,
// but it's much easier to just catch it here.
synchronized (this.monitor) {
int channelNumber = channel.getChannelNumber();
ChannelN existing = _channelMap.remove(channelNumber);
// Nothing to do here. Move along.
if (existing == null) return;
// Oops, we've gone and stomped on someone else's channel. Put it
// back and pretend we didn't touch it.
else if (existing != channel) {
_channelMap.put(channelNumber, existing);
return;
}
channelNumberAllocator.free(channelNumber);
}
}
public ChannelN createChannel(AMQConnection connection, int channelNumber) throws IOException {
ChannelN ch;
synchronized (this.monitor) {
if (channelNumberAllocator.reserve(channelNumber)) {
ch = addNewChannel(connection, channelNumber);
} else {
return null;
}
}
ch.open(); // now that it's been safely added
return ch;
}