concurrent

Type Members

1. abstract class Deferred[F[_], A] extends AnyRef

   

   A purely functional synchronization primitive which represents a single value which may not yet be available.

   A purely functional synchronization primitive which represents a single value which may not yet be available.

   When created, a Deferred is empty. It can then be completed exactly once, and never be made empty again.

   get on an empty Deferred will block until the Deferred is completed. get on a completed Deferred will always immediately return its content.

   complete(a) on an empty Deferred will set it to a, and notify any and all readers currently blocked on a call to get. complete(a) on a Deferred that has already been completed will not modify its content, and result in a failed F.

   Albeit simple, Deferred can be used in conjunction with Ref to build complex concurrent behaviour and data structures like queues and semaphores.

   Finally, the blocking mentioned above is semantic only, no actual threads are blocked by the implementation.

2. abstract class MVar[F[_], A] extends AnyRef

   

   A mutable location, that is either empty or contains a value of type A.

   A mutable location, that is either empty or contains a value of type A.

   It has the following fundamental atomic operations:

   • put which fills the var if empty, or blocks (asynchronously) until the var is empty again
   • tryPut which fills the var if empty. returns true if successful
   • take which empties the var if full, returning the contained value, or blocks (asynchronously) otherwise until there is a value to pull
   • tryTake empties if full, returns None if empty.
   • read which reads the current value without touching it, assuming there is one, or otherwise it waits until a value is made available via put
   • isEmpty returns true if currently empty

   The MVar is appropriate for building synchronization primitives and performing simple inter-thread communications. If it helps, it's similar with a BlockingQueue(capacity = 1), except that it doesn't block any threads, all waiting being done asynchronously (via Async or Concurrent data types, such as IO).

   Given its asynchronous, non-blocking nature, it can be used on top of Javascript as well.

   Inspired by Control.Concurrent.MVar from Haskell and by scalaz.concurrent.MVar.

3. abstract class Ref[F[_], A] extends AnyRef

   

   An asynchronous, concurrent mutable reference.

   An asynchronous, concurrent mutable reference.

   Provides safe concurrent access and modification of its content, but no functionality for synchronisation, which is instead handled by Deferred. For this reason, a Ref is always initialised to a value.

   The default implementation is nonblocking and lightweight, consisting essentially of a purely functional wrapper over an AtomicReference.

4. abstract class Semaphore[F[_]] extends AnyRef

   

   A purely functional semaphore.

   A purely functional semaphore.

   A semaphore has a non-negative number of permits available. Acquiring a permit decrements the current number of permits and releasing a permit increases the current number of permits. An acquire that occurs when there are no permits available results in semantic blocking until a permit becomes available.

   Blocking acquires are cancelable if the semaphore is created with Semaphore.apply (and hence, with a Concurrent[F] instance). Blocking acquires are non-cancelable if the semaphore is created with Semaphore.async (and hence, with an Async[F] instance).