4This is an implementation of Cloud Haskell, as described in
5/Towards Haskell in the Cloud/ by Jeff Epstein, Andrew Black, and Simon
7<http://research.microsoft.com/en-us/um/people/simonpj/papers/parallel/>),
8although some of the details are different. The precise message passing
9semantics are based on /A unified semantics for future Erlang/ by Hans
10Svensson, Lars-Åke Fredlund and Clara Benac Earle.
12For a detailed description of the package and other reference materials,
13please see the distributed-process wiki page on github:
14<https://github.com/haskell-distributed/distributed-process/wiki>.
17module Control.Distributed.Process
25 , liftIO -- Reexported for convenience
41 -- * Unsafe messaging variants
48 -- * Advanced messaging
74 -- * Process management
83 , ProcessTerminationException(..)
84 , ProcessRegistrationException(..)
93 -- * Monitoring and linking
105 , MonitorRef -- opaque
106 , ProcessLinkException(..)
107 , NodeLinkException(..)
108 , PortLinkException(..)
109 , ProcessMonitorNotification(..)
110 , NodeMonitorNotification(..)
111 , PortMonitorNotification(..)
128 , registerRemoteAsync
129 , reregisterRemoteAsync
130 , unregisterRemoteAsync
135 -- * Exception handling
153 -- * Local versions of 'spawn'
162import Control.Monad.IO.Class (liftIO)
163import Control.Applicative
164import Control.Monad.Reader (ask)
165import Control.Concurrent (killThread)
166import Control.Concurrent.MVar
172import Control.Distributed.Static
178import Control.Distributed.Process.Internal.Types
183 , ProcessMonitorNotification(..)
184 , NodeMonitorNotification(..)
185 , PortMonitorNotification(..)
186 , ProcessLinkException(..)
187 , NodeLinkException(..)
188 , PortLinkException(..)
189 , ProcessRegistrationException(..)
198 , LocalProcess(processNode)
202import Control.Distributed.Process.Serializable (Serializable)
203import Control.Distributed.Process.Internal.Primitives
219 -- Advanced messaging
245 -- Process management
247 , ProcessTerminationException(..)
260 -- Monitoring and linking
280 , registerRemoteAsync
281 , reregisterRemoteAsync
282 , unregisterRemoteAsync
288 -- Exception handling
307import Control.Distributed.Process.Node (forkProcess)
308import Control.Distributed.Process.Internal.Types
310 , withValidLocalState
312import Control.Distributed.Process.Internal.Spawn
313 ( -- Spawning Processes/Channels
321import qualified Control.Monad.Catch as Catch
323#if MIN_VERSION_base(4,6,0)
326import Prelude hiding (catch)
328import Control.Distributed.Process.Internal.StrictMVar (readMVar)
329import qualified Control.Exception as Exception (onException)
330import Data.Accessor ((^.))
331import Data.Foldable (forM_)
336-- 1. 'send' never fails. If you want to know that the remote process received
337-- your message, you will need to send an explicit acknowledgement. If you
338-- want to know when the remote process failed, you will need to monitor
339-- that remote process.
341-- 2. 'send' may block (when the system TCP buffers are full, while we are
342-- trying to establish a connection to the remote endpoint, etc.) but its
343-- return does not imply that the remote process received the message (much
344-- less processed it). When 'send' targets a local process, it is dispatched
345-- via the node controller however, in which cases it will /not/ block. This
346-- isn't part of the semantics, so it should be ok. The ordering is maintained
347-- because the ctrlChannel still has FIFO semantics with regards interactions
348-- between two disparate forkIO threads.
350-- 3. Message delivery is reliable and ordered. That means that if process A
351-- sends messages m1, m2, m3 to process B, B will either arrive all three
352-- messages in order (m1, m2, m3) or a prefix thereof; messages will not be
353-- 'missing' (m1, m3) or reordered (m1, m3, m2)
355-- In order to guarantee (3), we stipulate that
357-- 3a. We do not garbage collect connections because Network.Transport provides
358-- ordering guarantees only *per connection*.
360-- 3b. Once a connection breaks, we have no way of knowing which messages
361-- arrived and which did not; hence, once a connection fails, we assume the
362-- remote process to be forever unreachable. Otherwise we might sent m1 and
363-- m2, get notified of the broken connection, reconnect, send m3, but only
366-- 3c. As a consequence of (3b) we should not reuse PIDs. If a process dies,
367-- we consider it forever unreachable. Hence, new processes should get new
368-- IDs or they too would be considered unreachable.
370-- Main reference for Cloud Haskell is
372-- [1] "Towards Haskell in the Cloud", Jeff Epstein, Andrew Black and Simon
374-- http://research.microsoft.com/en-us/um/people/simonpj/papers/parallel/remote.pdf
376-- The precise semantics for message passing is based on
378-- [2] "A Unified Semantics for Future Erlang", Hans Svensson, Lars-Ake Fredlund
379-- and Clara Benac Earle (not freely available online, unfortunately)
381-- Some pointers to related documentation about Erlang, for comparison and
384-- [3] "Programming Distributed Erlang Applications: Pitfalls and Recipes",
385-- Hans Svensson and Lars-Ake Fredlund
386-- http://man.lupaworld.com/content/develop/p37-svensson.pdf
387-- [4] The Erlang manual, sections "Message Sending" and "Send"
388-- http://www.erlang.org/doc/reference_manual/processes.html#id82409
389-- http://www.erlang.org/doc/reference_manual/expressions.html#send
390-- [5] Questions "Is the order of message reception guaranteed?" and
391-- "If I send a message, is it guaranteed to reach the receiver?" of
393-- http://www.erlang.org/faq/academic.html
394-- [6] "Delivery of Messages", post on erlang-questions
395-- http://erlang.org/pipermail/erlang-questions/2012-February/064767.html
397--------------------------------------------------------------------------------
398-- Local versions of spawn --
399--------------------------------------------------------------------------------
401-- | Spawn a process on the local node
402spawnLocal :: Process () -> Process ProcessId
404 node <- processNode <$> ask
405 liftIO $ forkProcess node proc
407-- | Create a new typed channel, spawn a process on the local node, passing it
408-- the receive port, and return the send port
409spawnChannelLocal :: Serializable a
410 => (ReceivePort a -> Process ())
411 -> Process (SendPort a)
412spawnChannelLocal proc = do
413 node <- processNode <$> ask
416 _ <- forkProcess node $ do
417 -- It is important that we allocate the new channel in the new process,
418 -- because otherwise it will be associated with the wrong process ID
419 (sport, rport) <- newChan
420 liftIO $ putMVar mvar sport
424-- | Local version of 'call'. Running a process in this way isolates it from
425-- messages sent to the caller process, and also allows silently dropping late
426-- or duplicate messages sent to the isolated process after it exits.
427-- Silently dropping messages may not always be the best approach.
428callLocal :: Process a -> Process a
429callLocal proc = Catch.mask $ \release -> do
430 mv <- liftIO newEmptyMVar :: Process (MVar (Either Catch.SomeException a))
431 child <- spawnLocal $ Catch.try (release proc) >>= liftIO . putMVar mv
434 rs <- Exception.onException (takeMVar mv) $ Catch.uninterruptibleMask_ $
435 -- Exceptions need to be prevented from interrupting the clean up or
436 -- the original exception which caused entering the handler could be
437 -- forgotten. For instance, this could have a problematic effect
438 -- when the original exception was meant to kill the thread and the
439 -- second exception doesn't (like the exception thrown by
440 -- 'System.Timeout.timeout').
441 do mchildThreadId <- withValidLocalState (processNode lproc) $
442 \vst -> return $ fmap processThread $
443 vst ^. localProcessWithId (processLocalId child)
444 forM_ mchildThreadId killThread
446 either Catch.throwM return rs
keysesc to close
- j k
- move down, up
- enter
- open
- esc
- back, or up a level
- 1 2 3 4
- readme, files, commits, refs
- /
- filter
- y
- copy the clone command
- c
- compare the chosen commit with another (or shift-click both)
- ?
- show or hide this list