System.Posix.IO.Select.STM

Treat the POSIX select(2) function as a TMVar CInt.

Documentation

select :: [Fd] -> [Fd] -> [Fd] -> Timeout -> IO (TMVar CInt)

This version of select immediately returns and makes the return value of the select(2) call available as a TMVar CInt. See select for argument information.

selectOrTakeTMVar :: [Fd] -> [Fd] -> [Fd] -> Timeout -> TMVar a -> IO (Either CInt a)

The parameters are the same as for select, except for the addition of a TMVar. The function returns as soon as either the select(2) has completed, or the TMVar is full.

The return value is either the return value of select(2), or the content of the TMVar. If the TMVar becomes available first, then the select(2) call may hang around forever or until it times out (as specified by the Timeout parameter). If the select(2) returns before the TMVar is available, the TMVar is guaranteed to be left in place.

See also selectOrReadTChan and selectOrElse. Note that selectOrTakeTMVar and the former are special cases of the latter.

(Incidentally, selectOrTakeTMVar is the task I really wanted to accomplish, and solving it just turned into this little library).

selectOrElse :: [Fd] -> [Fd] -> [Fd] -> Timeout -> STM a -> IO (Either CInt a)

Analogous to selectOrTakeTMVar, except with a general STM action in place of taking a TMVar.

selectOrReadTChan :: [Fd] -> [Fd] -> [Fd] -> Timeout -> TChan a -> IO (Either CInt a)

Special case of selectOrElse where the STM action is reading a TChan.

data Timeout

A timeout of Never tells select(2) to never time out, while Time s us sets the timeout parameters to s seconds and us microseconds.

Constructors

Never

Time Seconds Microseconds