Marvin.Util.Mutable

Documentation

type Mutable v = IORef v

A mutable reference to a value of type v

This is like a pointer in c, the value behind which can be mutated by several functions. So long as they retain this reference they are able to retrieve the updated value.

newMutable :: MonadIO m => a -> m (Mutable a)

Create a new mutable reference of type v from an initial value.

readMutable :: MonadIO m => Mutable a -> m a

Retrieve the value behind by a mutable reference.

writeMutable :: MonadIO m => Mutable a -> a -> m ()

Set the value inside a mutable reference.

modifyMutable :: MonadIO m => Mutable a -> (a -> a) -> m ()

Change the value behind a mutable reference.

type Synchronized = MVar

A value that can be shared on multiple concurrent Threads.

This value works like a channel. It can either be empty or full. If it is empty writeSynchronized fills it, otherwise the write blocks. If it is full takeSynchronized empties, otherwise it blocks until it is filled. readSynchronized does not empty it and also blocks if the Synchronized is empty.

Should you just use it as a thread safe mutable variable, mutations typically follow the pattern:

  val <- takeSynchronized -- obtain the value and leave it empty to block concurrent reads
  mod <- modifyWithIO val -- modify the value, typically involves IO
  writeSynchronized mod -- write back the result

Another use for this type is as a message channel, where we have a producer and a consumer, the producer tries to write values into the Synchronized (writeSynchronized) and the consumer waits for the Synchronized to be filled and takes the value (takeSynchronized) for procesing.

It works generally best if any Synchronized is only used for one of these two applications at the same time.

This type is the same as MVar, only renamed for readability. If you want a more in depth documentation, see the documentation for MVar.

readSynchronized :: MonadIO m => Synchronized a -> m a

Read the vaue, but don't empty the Synchronized. Blocks if it is empty.

tryReadSynchronized :: MonadIO m => Synchronized a -> m (Maybe a)

Non blocking version of readSynchronized. Returns Nothing if it was empty.

takeSynchronized :: MonadIO m => Synchronized a -> m a

Read the value and empty the Synchronized, blocks if already empty.

tryTakeSynchronized :: MonadIO m => Synchronized a -> m (Maybe a)

Non blocking version of takeSynchronized, returns Nothing if it was empty.

writeSynchronized :: MonadIO m => Synchronized a -> a -> m ()

Fills the empty Synchronized with a value, blocks if it is full.

tryWriteSynchronized :: MonadIO m => Synchronized a -> a -> m Bool

Non blocking version of writeSynchronized. Returns False if it was full.

isEmptySynchronized :: MonadIO m => Synchronized a -> m Bool

Query if the Synchronized is empty or full.