Control.Concurrent.STM.RunOrElse

Documentation

runOrElse :: IO a -> STM b -> IO (Either a b)

runOrElse action stm runs the IO action action and attempts the STM operation stm, returning the return value which is available first. If action returns first, then stm is not run. If stm returns first, action may or may not complete, but its return value is discarded.

runOrTakeTMVar is a special case of this function, where stm is simply takeTMVar applied to the given TMVar.

runOrElse' :: STM a -> IO b -> IO (Either a b)

A version of runOrElse that prefers the STM operation to the IO action.

runOrTakeTMVar :: IO a -> TMVar b -> IO (Either a b)

This version of run takes an additional TMVar, and returns its content or the result of the IO action, depending on which is available first. Note that the action is not interrupted if the TMVar is the winner, so you may want to make sure it doesn't stick around forever.

runOrTakeTMVar action tm = runOrElse action (takeTMVar tm).

The function was originally made to support selectOrTakeTMVar, the reason this library exists.