Distributed Multi-Threading in GNU-Prolog

Distributed Multi-Threading in GNU Prolog Nuno Morgadinho, Salvador Abreu {nm, spa}@di.uevora.pt Departamento de Informática Évora 2007

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

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

What We Present • PM2 - a distributed multi-threading programming environment • GNU Prolog - efﬁcient native Prolog compiler • Combination of both Slide 4 ICLP ’07 CICLOPS

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

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

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

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

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

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

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

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

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

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

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

• 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

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

PM2-Prolog Remote Threads • thread_create/2 • vid(Rank, ThreadID) • Rank - VP identiﬁer • ThreadID - identiﬁer of the thread inside Slide 18 ICLP ’07 CICLOPS

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

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

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

Distributed Multi-Threading in GNU-Prolog

by Nuno Morgadinho on Nov 04, 2009

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Distributed Multi-Threading in GNU-Prolog — Presentation Transcript