Distributed Multi-Threading in GNU-Prolog
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This document discusses combining GNU Prolog with PM2 to enable distributed multi-threading capabilities. It presents an implementation where PM2 and GNU Prolog are connected without modifications. This allows GNU Prolog programs to execute across multiple computers through message passing. An execution model is described where a master node distributes work to worker nodes, which perform tasks and return results. Preliminary results show this approach achieves speedups for some real-world problems.
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Distributed Multi-Threading in GNU-Prolog
- 1. Distributed Multi-Threading in GNU Prolog Nuno Morgadinho, Salvador Abreu {nm, spa}@di.uevora.pt Departamento de Informática Évora 2007
- 2. Introduction • Distributed - one or more computers communicating over a network • Multi-Threading - more than one thread of execution • Thread - a flow of execution Slide 2 ICLP ’07 CICLOPS
- 3. Introduction • Obtain results faster for problems where performance is critical • The problem can be divided into smaller tasks which can be carried out simultaneously • Parallelism Slide 3 ICLP ’07 CICLOPS
- 4. What We Present • PM2 - a distributed multi-threading programming environment • GNU Prolog - efficient native Prolog compiler • Combination of both Slide 4 ICLP ’07 CICLOPS
- 5. GNU Prolog and PM2: Why? • GNU Prolog produces stand-alone executables • The size of the executables is relatively small • Doesn’t work with machine independent saved- states Slide 5 ICLP ’07 CICLOPS
- 6. Implementation • Established a model for connecting PM2 and GNU Prolog • The approach doesn’t involve modifications to GNU Prolog neither to PM2 • Compatibility with GNU Prolog libraries is retained Slide 6 ICLP ’07 CICLOPS
- 7. Approach • Tabard - new program that manages distributed instances of GNU Prolog engines • pm2prolog - new library that allows the development of distributed multithreaded Prolog applications Slide 7 ICLP ’07 CICLOPS
- 8. Functionality • Allow to execute computations remotely • Manage the engines responsible for the computations • Manage the communication involved between the several machines • Based on distributed memory and explicit message-passing Slide 8 ICLP ’07 CICLOPS
- 9. Example :- initialization(init). :- include('pm2prolog'). % thread with rank 0 init:- pm2_is_master, !, pm2_max_rank(MaxRank), start_prolog_workers(MaxRank), test_prolog_workers(MaxRank), read_test(MaxRank), stop_prolog_workers. % thread != 0 init:- worker_code. Slide 9 ICLP ’07 CICLOPS
- 10. Before Running • Configuration that specifies the list of machines • Each machine is mapped to one or more processing nodes or virtual processors (VPs) Slide 10 ICLP ’07 CICLOPS
- 11. Execution Model • Binary is copied to all machines • In VP0 (master) a gprolog engine is created • In the other VPs (workers) a pthread in C is created and stands awaiting messages Slide 11 ICLP ’07 CICLOPS
- 12. Execution Model • In the master, now in the Prolog thread, a predicate is called to send a message to every worker • The workers receive the message, initiate a gprolog engine and the thread stands awaiting more messages to come Slide 12 ICLP ’07 CICLOPS
- 13. Execution Model • In the master, work is distributed throughout the workers through message-passing • The workers receive tasks which they execute locally. As soon as they finish, they send their results back to the master Slide 13 ICLP ’07 CICLOPS
- 14. Execution Model • The master assembles the work results by reading as many messages as the number of previously sent messages • The master redistributes work again or orders the workers to finish their execution • The workers terminate • The master reiniciates the workers or terminates itself Slide 14 ICLP ’07 CICLOPS
- 15. Inside a Virtual Processor UNLOCK Message Queue LOCK WRITE READ WRITE ... C Thread Listener Prolog Thread write_message_queue() thread_send_message/2 Start_Prolog() thread_get_message/2 Stop_Prolog() pm2_self/1 ... ... RECEIVE SEND SOCKET Slide 15 ICLP ’07 CICLOPS
- 16. • Several VPs per physical machine is possible Node 1 Node 2 VP 2 VP 0 Prolog Proc Prolog Proc Node 3 VP 1 VP 2 Prolog Prolog Proc Proc ... ... Slide 16 ICLP ’07 CICLOPS
- 17. ISO Support • ISO/IEC Draft Technical Report 13211-5:2007, Prolog Multi-Threading Support • Extensions to take into consideration remote threads Slide 17 ICLP ’07 CICLOPS
- 18. PM2-Prolog Remote Threads • thread_create/2 • vid(Rank, ThreadID) • Rank - VP identifier • ThreadID - identifier of the thread inside Slide 18 ICLP ’07 CICLOPS
- 19. Experimental Evaluation 100 75 50 25 0 2004 2005 2006 2007 Results obtained with 7x Intel(R) Pentium(R) 4 2.80 Mhz each, Hyperthreading enabled, 512 Mbytes each, Linux 2.4.19 kernel, 100 Mbits TCP/IP Ethernet network Slide 19 ICLP ’07 CICLOPS
- 20. Conclusions • We presented a distributed multi-threading GNU Prolog system on top of PM2 • First results show that it can obtain substantial speedups, even for real-world • Proved the approach to be technically possible and can be of use to other implementers Slide 20 ICLP ’07 CICLOPS
- 21. Further Work • Improving our proposal • Extend the API with introspection and monitoring predicates • Experiment with more programs and bigger configurations • Build our own applications using this technology Slide 21 ICLP ’07 CICLOPS