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| The GPH Language |
Glasgow Parallel Haskell, or GPH for short, is a non-strict parallel functional programming language. GPH is an extension of Haskell, adding a primitive for parallel composition par, that is used together with sequential composition seq to express how a program should be evaluated in parallel.
| Download |
Glasgow Parallel Haskell (GPH) is implemented as a special setup of the Glasgow Haskell Compiler (GHC). Recent GPH versions are available as source or binary bundles from our FTP server (see below). You must also download and install PVM (Parallel Virtual Machine), if you want to execute programs on several processors.
gum-4-06.
The unstable branch of development is GUM-6.6 and it is currently being tested on a Beowulf cluster. The unstable branch is available as a source bundle upon request to the mailing list.
Ports to other architectures (available on request):
| Documentation |
| Papers |
The following web page gives a list of selected papers covering all aspects of GPH. On other pages, recent papers and papers on architecture independence are available.
| Current Developments |
The main direction in developing the parallel runtime-system further is towards architecture-independent parallelism. We are at the moment extending the GUM system with new mechanisms for load balancing and work distribution in order to improve the performance on high-latency machines. This work is summarised in a separate web page on architecture-independent parallelism.
Another strand of research is improved performance prediction of GPH. We are currently working on an operational semantics for GPH, which will allow us to predict the amount of parallelism generated by a particular evaluation strategy.
Closely related to GPH is a new language designed for the distributed execution of Haskell programs: GdH (Glasgow distributed Haskell). We have just finished a first implementation of GdH and tried it on a couple of distributed applications. At the moment we are investigating possibilities of adding fault tolerance to this system. You can find details at the GdH Home Page.
| Activity reports |
| GPH Algorithms Repository |
The parallel algorithms library for GPH is rather dated by now but still available. To get a set of test programs better download the following source bundle of test programs for GUM-4.06.
| Mailing List |
The GPH mailing list exists to keep people informed about the use and
implementation of the GPH programming language:
gph@macs.hw.ac.uk.
To join/leave the mailing list, or look up the archives, visit this web page.
| Developing Parallel Programs |
The great thing about GPH is that it's so easy to take a sequential program written in Haskell, and add par and seq annotations to make it parallel. However, to get the best parallelism out of your code isn't always trivial, so tools and libraries have been developed to make the process easier. Here's a recommended list of things to help with program development:
Guidelines on developing large parallel functional programs with GPH are in the following paper:
GranSim For simulating GPH on a single processor; Strategies A library that provides better abstraction and common parallel strategies; Profiling To visually show the behaviour of your parallel program.
- Engineering Large Parallel Functional Programs
- Hans-Wolfgang Loidl and Phil Trinder, IFL, 1997.
| Evaluation Strategies |
Annotating a program with par and seq can obfuscate the code. A more advanced means of abstraction is possible that allows the structure to remain intact, but with additional suffixes that describe its parallel execution. This new abstraction is provided by using higher-order functions, that have been dubbed evaluation strategies. A library of common parallel programming strategies has been developed, and is described in the paper:
- Algorithm + Strategy = Parallelism, HTML
- Kevin Hammond, Hans-Wolfgang Loidl, Simon Peyton Jones, and Phil Trinder, JFP 8(1), 1998.
| Simulating Parallelism (GranSim) |
Before running programs on a parallel machine, it is recommended that you first simulate your code on a single processor. The simulator called GranSim allows you to control a whole variety of parameters, including message latency, and collects more detailed execution profiles than the real parallel implementation does. When developing programs it is particularly useful to get GranSim to simulate an ideal architecture, i.e. a machine with infinite processors, and no communication cost. More details can be found on GranSim's homepage, and in the user 's guide:
- GranSim user's guide, HTML
- Hans-Wolfgang Loidl, 1996.
| Parallel Execution (GUM) |
GUM is the name of the runtime system that provides support on real parallel architectures. Communication between processors is facilitated by using the message-passing library PVM in a Unix environment. Since abstract C is used as the intermediate language, GPH is available on any architecture that provides both gcc and PVM. GUM has also been ported to other message-passing libraries such as MPI and Thinking Machines CMMD, although these ports have not been released. The following paper fully describes GUM:
- GUM: a portable parallel implementation of Haskell.
- Kevin Hammond, Jim Mattson, Andrew Partridge, Simon Peyton Jones, and Phil Trinder, PLDI, 1996.
| Ports |
GUM is currently available on the following parallel architectures:
| Architecture | Constructor(s) | |
| Shared-memory multiprocessor | Sun Solaris | Glasgow folk |
| Networks of workstations | Sun Solaris | |
| DEC Alpha | ||
| Intel Linux | Ed Barry | |
| Distributed-memory multiprocessor | Thinking Machines CM5 | Kei Davis |
Please let us know if you you have ported GPH to any other platforms not listed here by e-mailing gph@macs.hw.ac.uk.
| Profiling |
Both GranSim and GUM produce log files which are profiles of the parallel execution of a program. These log files can be converted to PostScript with scripts that are included with the GPH compiler. Some examples can be found on the GranSim homepage.
| Applications |
The following papers all describe large applications that have been written with GPH:
- Parallelising a Large Functional Program; Or: Keeping LOLITA Busy
- Hans-Wolfgang Loidl, Richard Morgan, Phil Trinder, Sanjay Poria, Chris Cooper, Simon Peyton Jones, and Roberto Garigliano, IFL, 1997.
- A Case Study of Data-intensive Programs in Parallel Haskell
- Phil Trinder, Kevin Hammond, Hans-Wolfgang Loidl, Simon Peyton Jones, and J. Wu, Glasgow FP Workshop, 1996.
- LinSolv: a Case Study in Strategic Parallelism
- Hans-Wolfgang Loidl, Glasgow FP Workshop, 1997.
- Naira: A Parallel 2 Haskell Compiler
- Sahala Junaidu, Tony Davie, and Kevin Hammond, IFL, 1997.
- Refining a Parallel Algorithm For Calculating Bowings
- Cordy Hall, Hans-Wolfgang Loidl, Phil Trinder, Kevin Hammond, and John O'Donnell, Glasgow FP Workshop, 1997.
| People |
The following list includes past and present developers, users, and people that have a serious interest in GPH.
| Projects |
- APART 624
- The APART project focusses on achieving architecture-independent parallelism with GPH and extensions to the current runtime-system.
- APSET
- APSET is a project being carried out at the Open University and Heriot-Watt University to provide better profiling tools for GPH.
- Eden
- Eden is a parallel functional language that is being implemented by extending GHC.
- Instances generator for Haskell
- A Haskell preprocessor that is particularly useful for generating instances of the class NFData, that is used by evaluation strategies.
| Workshops |
- Glasgow FP Workshops
- The functional programming group at Glasgow organises an annual workshop covering all aspects of functional programming.
- IFL
- The International Workshop on Functional Languages has been held annually since 1989, and covers research related to the implementation of functional languages. Here are some links to IFL workshops: Norwich 1994, Bonn 1996, St. Andrews 1997, London 1998, Aachen 2000, Stockholm 2001.
- SCOFPIG
- The Scottish Functional Parallel Interest Group is an informal collection of researchers that are interested in parallel functional programming. Meetings are held two or three times a year at a Scottish University.
- Scottish FP Workshops
- The Scottish Universities that are active in functional programming organise an annual workshop. Participation is open, and the workshop covers all aspects of functional programming.