The Grid-Occam Project

1
The Grid-Occam Project

• Dipl.-Inf. Bernhard Rabe
• Dipl.-Inf. Peter Tröger
• Dr. Martin von Löwis
• Prof. Dr. rer. nat. habil. Andreas Polze
• Operating Systems Middleware Group
• Hasso-Plattner-Institute, University of Potsdam

2
Outline

• Introduction into Occam
• The Grid-Occam Idea
• The Grid-Occam lecture
• Grid-Occam programs
• Conclusions

3
Occam History

• Based on Sir T. Hoares ideas of Communicating
  Sequential Processes (CSP)
• Parallel processing language
• Abstraction from underlying hardware, software
  and network environment
• Developed by INMOS for transputer systems
• Distributed memory system
• 4 high-speed hardware links
• Routing of messages for unconnected processors
  (virtual channel router)

4
Occam Language

• Primitive actions
• Variable assignment
• Channel output
• Channel input
• SKIP
• STOP
• Sequential process combination (SEQ)
• Parallel process combination (PAR)

PROC hello() INT x,y CHAN OF INT c,d PAR
SEQ c ! 117 d ? x SEQ c ? y d ! 118
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ALT and Arrays

• Alternative process combination (ALT)
• Arrays

ALT keyboard ? var1 to.computer ! var1
from.computer ? var1 screen ! var1
VALUE num.of.fields IS 500 num.of.fieldsREAL64
a,b num.of.fieldsCHAN OF REAL64 c
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Rules in Occam

• Rendezvous behavior of channels
• Receiver blocks until the sender wrote the value
• Sender continues after the receiver read the
  value
• Variables can only be written by one process in
  parallel
• Likewise, only a single process can read from a
  channel, and another single process can write to
  the channel

7
Building a Grid Application
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The Grid-Occam Idea

• Bring parallelism as first-level language
  construct to modern distributed environments
• Consistent programming model for different
  granularities of distribution (threads, cluster
  nodes, grid nodes)
• Support for heterogeneous execution platforms
• .NET implementation on Rotor (MacOS X, Windows,
  FreeBSD)
• Integration of legacy source code (e.g. Fortran)
• Clear distinction of language compiler and
  infrastructure-dependent runtime library
• Multithreaded runtime library
• MPI runtime library
• Grid runtime library
• Support nested nature of granularity levels

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Compiler and Libraries

• Occam compiler
• Generates C code
• Code utilizes common interface for all runtime
  library implementations
• Multithreaded (MT) runtime library
• Channels with interlocked shared memory,
  rendezvous behavior through multiple semaphore
  locks
• Shared memory for global variables
• .NET threads for parallel Occam processes
• MPI runtime library
• Minimal topology information (RANK, SIZE)
• Fully interconnected node topology
• Fine-granular parallel execution on one node by
  using the MT library
• Rendezvous channels through synchronized send
  operation

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Grid Runtime Library Idea

• Grid-Occam as coordination language
• External code represented as Occam procedure
• Runtime library submits external executable to a
  grid resource
• Usage of standard job submission APIs (DRMAA,
  GAT, COG)
• Best-effort process placement
• Utilize infrastructure information (e.g. MDS)
• Consideration of channel bandwidth information
  (NWS)
• (Partial) task graph generated by the compiler
• Mapping algorithms from cluster research
  community
• Distributed computation in the Grid
• Based on Grid-enabled MPI (Mpich-G2)
• Based on WSRF services (Occam channel service)
• Proof of concept
• Expose web services / WSRF services as Occam
  channel

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Grid-Occam Execution Environment
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The Accompanying Lecture

• Run in Summer semester 2004
• 5 groups of 3-4 students
• All groups produced .NET-based distributed
  runtime environments for Occam
• Runtime environments
• Support for SEQ, PAR, ALT
• Hello World using 2 processes/2 channels as
  initial assignment
• pthread-implementation of runtime was given to
  students
• Compiler construction
• Focus on tools ANTLR, Coco/R, lex/yacc, kimwitu,
  
• All compilers support a common Occam subset and
  different extensions

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Translated into C

• namespace Occam.UserCode
• public class Parallel0 Occam.DistributedSequ
  ence
• int _x_3 Occam.Channel _d_2
  Occam.Channel _c_1
• public Parallel0(int _x_3, Occam.Channel
  _d_2, Occam.Channel _c_1)
• this._x_3 _x_3
• this._d_2 _d_2
• this._c_1 _c_1
• public override void Run()
• _c_1.Write((int)(117))
• _x_3 (int)_d_2.Read()
• public void Result(out int _x_3)
• _x_3 this._x_3
• public class Parallel1 Occam.DistributedSequ
  ence

public class MainClass
ProgramEntry public static void
_main5() Occam.Channel _c_1
new Occam.Channel(), _d_2 new
Occam.Channel() int _x_3 0
Parallel0 parallel0 (Parallel0)Runtime.Crea
teSequence(typeof(Parallel0 ), _x_3, _d_2,
_c_1) int _y_4 0
Parallel1 parallel1 (Parallel1)Runtime.CreateSeq
uence(typeof(Parallel1 ), _y_4, _d_2, _c_1)
Occam.Runtime.Parallel(parallel0,
parallel1) parallel0.Result(out
_x_3) parallel1.Result(out _y_4)

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Translated into C (2nd approach)
public virtual void SEQ1()
WriteChannel c1__cf.getWriteChannel("c1")
c1__.write(117) ReadChannel
d1__cf.getReadChannel("d2") x3_
((System.Int32)d1__.read() )
public virtual void SEQ2()
ReadChannel c2__cf.getReadChannel("c1")
y4_ ((System.Int32)c2__.read() )
WriteChannel d2__cf.getWriteChannel("d2")
d2__.write(118)
OccamMainProcess() public virtual
void PAR1() ArrayList
occamProcesses new ArrayList()
occamProcesses.Add(new OccamProcess(SEQ1))
occamProcesses.Add(new OccamProcess(SEQ2))
env.execPAR(occamProcesses)

• OccamProgram()
• public class MyOccamProgram
• private IExecutionEnvironment env
• private ChannelFactory cf
• private IVariableStore vs
• private int x3_ private int y4_
• public MyOccamProgram(IExecutionEnvironmen
  t executionEnvironment)
• envexecutionEnvironment
• cfenv.getChannelFactory()
• public MyOccamProgram(MyOccamProgram
  originalProcess)
• envoriginalProcess.env
• cforiginalProcess.cf
• x3_originalProcess.x3_
• y4_originalProcess.y4_
• public static void Main(string args)
• BootstrapLoader loader new
  BootstrapLoader(args, Assembly.GetCallingAssembly(
  ))

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Optimizing Datamanagement

• PROC hello()
• INT x,y
• CHAN OF INT c,d
• PAR
• SEQ
• c ! 117
• d ? x
• SEQ
• c ? y
• d ! 118

PROC hello() CHAN OF INT c,d PAR INT x
SEQ c ! 117 d ? x INT y SEQ c ?
y d ! 118
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Conclusions

• First implementation of Occam in common
  intermediate language, and also the first
  implementation that implements Webservice
  channels in Occam.
• Investigation of paradigms, design patterns and
  implementation techniques for enhancing
  middleware technology for predictable computing.
• Linking grid computing and parallel computing
  techniques.
• Teaching compiler construction, concurrent
  programming, (weakly consistent) distributed
  shared memory models.

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Thank you, any questions ?
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