System.Cache.Impl.MVar

Safer cache version that is implemented totally on the user level. Using MVar as a synchronization primitive.

While this implementation is slower in general case it may be more resilient to changes in GHC and RTS. This implementation is mostly used in order to sanity check the GHC one, and in order to be able to switch to this one without program recompilation.

However if you need strict guarantees that the only one action with the same input is run concurrently you should prefer this implementation.

Documentation

new :: (Show a, Hashable a, Ord a) => Config -> IO (Handle a b)

Create new cache handle. Keeps priority queue from psqueues package inside.

Properties:

• if multiple threads are running an IO action with the same input concurrently then only one will run, all the rest will wait for that action and will either return a value, or throw an exception depending on the the result of the first one
• storage is cleared only during access, it will remove redundant work but may lead to the situation when cached values are stored in memory for a longer period that it was expected
• psqueue structure uses both Hashable and Ord constraints and is not vulnerable to the hash collision attacks.