STM slightly conservative on write-only transactions
The STM appears to be slightly too conservative on write-only transactions.
It will store a copy of the current (that is, old) value on a writeTVar, even if it was never read from. This can cause a spurious retry.
E.g. atomically $ writeTVar tv 0 really has no reason to ever retry. Neither, in fact, does atomically $ mapM (\tv -> writeTVar tv 0) [tv1,tv2,tv3,tv4].
My suggestion is to instead indicate "no prior value" for that TVar, and then make no consistency checks on TVars marked as no prior value...
Jules
Trac metadata
| Trac field | Value |
|---|---|
| Version | 6.8.1 |
| Type | Bug |
| TypeOfFailure | OtherFailure |
| Priority | normal |
| Resolution | Unresolved |
| Component | Compiler |
| Test case | |
| Differential revisions | |
| BlockedBy | |
| Related | |
| Blocking | |
| CC | |
| Operating system | Unknown |
| Architecture | Unknown |