Control.CUtils.Deadlock

Automatic deadlock prevention.

Automatic deadlock detection is inefficient, and computations cannot be rolled back or aborted in general.

Instead, I prevent deadlocks before they happen.

Documentation

data Res t u where

The typical sequence that produces a deadlock is as follows:

1. Thread 1 acquires lock A
2. Thread 2 acquires lock B
3. Thread 1 tries to acquire B
4. Thread 2 tries to acquire A

Deadlock.

Standard deadlock detection intervenes after (4) has occurred. I intervene in a lock acquisition that is followed by an unsafe schedule (here at (2)). I suspend thread 2 until a safe schedule is guaranteed -- in this case until thread 1 relinquishes lock A.

The Res arrow.

Computations are built with these constructors (and the arrow interface). Pieces of the arrow that hold locks have to be finitely examinable, Locks have to be used with the Acq and Rel constructors.

Constructors

Lift :: Kleisli IO t v -> Res v u -> Res t u

Acq :: MVar () -> Res t u -> Res t u

Rel :: MVar () -> Res t u -> Res t u

Fork :: Res t () -> Res t u -> Res t u

Plus :: Res t v -> Res u v -> Res (Either t u) v

Id :: Res t t

Instances

Arrow Res

ArrowChoice Res

Strict Res

Concurrent Res

Category * Res

liftK :: (t -> IO u) -> Res t u

lft :: IO v -> Res v u -> Res b u

acq :: MVar () -> Res u u

rel :: MVar () -> Res u u

fork :: Res t () -> Res t u -> Res t u

run :: Res t u -> t -> IO u

Use this to run computations built in the Res arrow.