Josef Svenningsson wrote:
What I want to know boils down to this: what order are processes run which have been woken up from a call to retry?
IIUC, the order of wake up is irrelevant, since *all* the threads will re-run the transaction in parallel. So, even if thread 1 is the first to wake up, thread 2 might beat it in the race, and complete its transaction first. The execution model should be roughly this one: do not lock anything, run every read/write to TVar's in parallel, performing copy-on-write so that isolation is preserved. When the transaction ends, commit the data written in c-o-w's: lock everything, check that previously read data is still the same, and if it is overwrite the master copy of Tvars, unlock everything. I suggest you put some random delay in your fairness tests, maybe using unsafeIOtoSTM, so that you can improve starvation ;-) Also, try running a very slow (much-delayed) transaction againts several fast ones. I expect the slow one will never reach completion. AFAIK, achieving fairness in STM can be quite hard (not unlike other mainstream approaches to concurrency, sadly). Zun.