Re: Proposal: Add tryReadChan to Chan

On 01/12/2010 00:25, Mitar wrote:

Hi!

On Wed, Dec 1, 2010 at 12:55 AM, Antoine Latter wrote:

...

All of this really feels like what STM is good at. It might help if you explained why TChans are not well suited to your task.

Because it has too much overhead (I haven't tested it for my particular application but it is based on comment for isEmptyChan). I understand that Chans are more lightweight and once isEmptyChan was deprecated I discovered that for my purposes (non-blocking read) I do not need isEmptyChan and that code can be written without problems isEmptyChan has (mostly because there is a subtle change in semantics).

Chan and TChan have approximately the same performance, based on some simple benchmarks we did back when we implemented STM. All the exception-safety stuff slows down Chan - those modifyMVars aren't cheap. It's possible things may have changed though, it was a while since we did those measurements. If you have many threads beating on the same Chan, then in that case the STM version may be a lot slower because it doesn't have the single-wakeup property that MVars have. That's the tradeoff. Cheers, Simon