#15267: Extend TVar/MVar to N capacity / Add primitive channal type -------------------------------------+------------------------------------- Reporter: winter | Owner: (none) Type: feature request | Status: new Priority: high | Milestone: 8.6.1 Component: Runtime System | Version: 8.4.3 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Description changed by winter: Old description:

The current concurrent primitives `TVar` and `MVar` have a fixed single capacity for holding the value to be synchronized. This pose great limitations on implementing many higher level concurrent structures efficiently, e.g. bound channel, semaphore, resource pool, etc. For example current http://hackage.haskell.org/package/base-4.11.1.0/docs/src/Control.Concurrent.QSem.html#signalQSem> is not ideal due to the extensive usage of multiple `MVar` s. If we have a good `BoundedChan a` type, semaphores can be easily implemented with `BoundedChan ()`.

Currently we have various bound channel implementations, but these implementations are often not very efficient or too complex. For example the `BoundedChan` from http://hackage.haskell.org/package/BoundedChan-1.0.3.0/docs/Control- Concurrent-BoundedChan.html> is based on an array of `MVar` s, thus consumes much more memory than a primitve channel which only have to record parked `StgTSO` s.

I'm thinking adding something like:

``` typedef struct { StgHeader header; struct StgMVarTSOQueue_ *head; struct StgMVarTSOQueue_ *tail; StgInt capacity; // the channel's capacity StgInt read_index; // the reading end's index StgInt write_index; // the writing end's index StgClosure *payload[]; // payload array in continuous memory } StgMChan; ```

I still can't work out all the details, but I'm confident something similar to this will work.

New description: The current concurrent primitives `TVar` and `MVar` have a fixed single capacity for holding the value to be synchronized. This pose great limitations on implementing many higher level concurrent structures efficiently, e.g. bound channel, semaphore, resource pool, etc. For example current [http://hackage.haskell.org/package/base-4.11.1.0/docs/src/Control.Concurrent... semaphore's implementation] is not ideal due to the extensive usage of multiple `MVar` s. If we have a good `BoundedChan a` type, semaphores can be easily implemented with `BoundedChan ()`. Currently we have various bound channel implementations, but these implementations are often not very efficient or too complex. For example the `BoundedChan` from [http://hackage.haskell.org/package/BoundedChan-1.0.3.0/docs/Control- Concurrent-BoundedChan.html BoundedChan] is based on an array of `MVar` s, thus consumes much more memory than a primitve channel which only have to record parked `StgTSO` s. I'm thinking adding something like: {{{ typedef struct { StgHeader header; struct StgMVarTSOQueue_ *head; struct StgMVarTSOQueue_ *tail; StgInt capacity; // the channel's capacity StgInt read_index; // the reading end's index StgInt write_index; // the writing end's index StgClosure *payload[]; // payload array in continuous memory } StgMChan; }}} I still can't work out all the details, but I'm confident something similar to this will work. -- -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/15267#comment:1 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler

#15267: Extend TVar/MVar to N capacity / Add primitive channel type -------------------------------------+------------------------------------- Reporter: winter | Owner: (none) Type: feature request | Status: new Priority: high | Milestone: 8.8.1 Component: Runtime System | Version: 8.4.3 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Changes (by lelf): * cc: lelf (added) -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/15267#comment:4 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler