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mpjdev, the low-level MPJ device
Aamir Shafiaamir.shafi@port.ac.uk
Distributed Systems Group12th March, 2004
Sequence Introduction
History of MPJ Overview of java.nio package ‘mpjdev’ implementation
Introduction Packing/Unpacking at the device level Communication Protocols
Eager Send Rendezvous Protocol
Quick Start Guide to mpjdev What’s next
Trinity: Neo... No one has ever done anything like this.Neo: That's why it's going to work.
Introduction Parallel Programming
Shared Memory Message Passing
Message Passing MPI PVM
Has Java got what it takes to be a parallel programming language ?
Message Passing in Java (MPJ)
Specification Document mpiJava 1.2.5
Uses native MPI
Pure java MPI-like libraries mpiJava 1.2.5
Uses native MPI Best candidate to be developed to MPJ http://www.hpjava.org/mpiJava.html DSG’s project MPJ (http://dsg.port.ac.uk/projects/mpj/) is tightly
coupled to this effort JMPI
Drawback, based on RMI http://euler.ecs.umass.edu/jmpi/
MPJava Based on java.nio Results encouraging No source-code
DOGMA – Dead MPP –
Basic library http://www.mi.uib.no/~bjornoh/mtj/mpp/
Sequence Introduction
History of MPJ Overview of java.nio package ‘mpjdev’ implementation
Introduction Packing/Unpacking at the device level Communication Protocols
Eager Send Rendezvous Protocol
Quick Start Guide to mpjdev What’s next
Oracle: You're cuter than I thought. I can see why she likes you.
New I/O overview Buffer classes,
Conversion among basic data types Direct and Indirect Buffer
Scalable Applications No more “one thread per client” One thread, many clients
Multiplex Synchronous I/O using the selectors
SocketChannel – New Abstraction Pipe – One way communication
Buffer classes in java.nio
‘T’Buffer classes, ‘T’ being all the basic data types
Any basic data type can be copied onto the ByteBuffer, (the basic primitive)
Buffer can be, Direct, allocateDirect(int) Indirect, allocate(int)
a. ByteBuffer buffer = ByteBuffer.allocate(8);b. buffer.putInt(4);c. buffer.flip();
a. ByteBuffer buffer = ByteBuffer.allocate(8);b. ByteBuffer buffer = ByteBuffer.allocateDirect(8);
Selector
Selector provide, connecting, accepting, reading & writing facilities to the SocketChannel OP_WRITE, OP_READ, OP_ACCEPT,
OP_CONNECT Depends on native OS facilities
Selection performs differently on Windows and Linux
Sequence of events for selectors
Taming the NIO circus Taming the NIO circus thread
http://forum.java.sun.com/thread.jsp?forum=4&thread=459338&start=0&range=15&hilite=false&q=
OutOfMemory Exception http://forum.java.sun.com/thread.jsp?thread=433702&f
orum=4&message=2136979 Selectors taking cent percent CPU
http://forum.java.sun.com/thread.jsp?forum=11&thread=494967
http://forum.java.sun.com/thread.jsp?forum=4&thread=494194
J2SE 1.5.0 beta solves many problems
Sequence Introduction
History of MPJ Overview of java.nio package ‘mpjdev’ implementation
Introduction Packing/Unpacking at the device level Communication Protocols
Eager Send Rendezvous Protocol
Quick Start Guide to mpjdev What’s next
Neo: What are you trying to tell me? That I can dodge bullets?Morpheus: No, Neo. I'm trying to tell you that when you're ready, you won't have to.
mpjdev – Introduction
What is device ? Sockets
Similar to ADI in MPICH Meant for library developers (MPJ),
not application programmers jGMA can use mpjdev
mpjdev – Introduction Single JVM Implementation
Processes are threads in the single JVM Native implementation
Uses native MPI LAPI Implementation
Eager-send Rendezous
Buffer packing/unpacking are taken from these implementations
mpjev functions Comm methods
Void send(Buffer, int dest, int tag) Req isend(Buffer, int dest, int tag) Req irecv(Buffer, int src, int tag)
For src, ANY_SRC For tag, ANY_TAG
Status recv(Buffer, int dest, int tag)
Req methods Status Wait() Status Wait(Req[])
‘mpjdev’ – Connectivity
Communication Protocols – Eager Send
Sender Receiver
Sel Sel
1 2 3 4 5 6
Huge Memory at Receiver
Rendezvous Protocol
1
Sender Queue
1
Recv Queue
Sender
Sel Sel
1
Receiver
1
Sender 1:
Sender posts send(), Req stored in Queue
Sender 2:
Sender sends the control message asking if matching recv is posted ?
Sender 3:
Sender receives response confirming there is a matching recv
Sender 4:
Sender sends the actual data
Receiver 1:
Checks if step 2 has already posted recv, if yes, initiates step 3, else posts a req in Que
Receiver 2:
Checks if step 1 has posted a recv request, if yes, initiates step 3, else posts a request.
NOTE :- STEP 1 & 2 needs synchronization
Receiver 3:
Writes back to sender that recv’r is ready to receive
Receiver 4:
Receives the data
Packing/Unpacking of Buffers write(t[] source, int offset,int length) gather(t[] source, int numEls, int offs,
int [] indexes) strGather(t[] source, int srcOff, int
rank, int exts, int strs, int [] indexes) read(t[] dest, int dstOff, int numEls) scatter(t[] dest, int numEls, int offs, int
[] indexes) strScatter(t[] dest, int dstOff, int rank,
int exts, int strs, int [] indexes) Java objects, same concepts
Message Format Primary header (Eight bytes),
First four bytes –nothing Last four byte --size of message
Primary PayLoad, Each primitive data type is written as a section,
SECTION_HEADER (8 bytes) First byte – Type of Message, int, float etc Last four bytes – Number of Elements in this section
SECTION_DATA The actual data itself Should be multiple of 8
Secondary header (Eight Bytes) First Four bytes –nothing Last Four bytes – Size of Java Object
Secondary PayLoad Actual java Object in bytes
Can Java object be written as a section in Primary Payload ?
Message Format, Single Section
int intArray[] = new int[2];
int[0] = 1; int[1] = 2;
WriteBuffer wBuffer = new WriteBuffer(24);
wBuffer.write(intArray, 0,2); wBuffer.pack();
X X X X Size (24) int T X X X 2(NoEls) int[0] int[1]
PRIMARY_HEADER SECTION_HEADER SECTION_HEADER
8 bytes 8 bytes 8 bytes
Message Format, Multiple Section
int intArray[] = new int[2]; long longArray = new long[2];
int[0] = 1; int[1] = 2; longArray[0] = 1L; longArray[1] = 2L;
WriteBuffer wBuffer = new WriteBuffer(48);
wBuffer.write(intArray, 0,2); wBuffer.write(longArray, 0,2);
wBuffer.pack();
X X X X Size (24) int X X X 2(NoEls) int[0] int[1] L X X X 2 long[0] long[1]
PRIMARY_HEADERSECTION_HEADERSECTION_DATA
8 bytes 8 bytes 8 bytes
S_HEADER S_DATA
8 bytes 16 bytes
Control Messages
Used in Rendezvous Protocol Format
Int – Rank of Destination Int – Rank of Source Int – Message Length Int – Message Tag
Should be as small as possible
Sequence Introduction
History of MPJ Overview of java.nio package ‘mpjdev’ implementation
Introduction Packing/Unpacking at the device level Communication Protocols
Eager Send Rendezvous Protocol
Quick Start Guide to mpjdev What’s next
Morpheus: There is a difference between knowing the path and walking thepath.
Directory Structure
Compiling the source files
Dependencies, J2SE1.5.0-beta Apache Ant (1.6.1)
If you want to compile from the source, otherwise
mpjdev.jar is lying in the mpjdev/lib folder
You need to add “mpjdev.jar” in your CLASSPATH
Running Examples - Config
Configuration mpjdev/conf/mpjdev.conf Total Number of Processes For each Process
FULLY_QUALIFIED_NAME@PORT@RANK Sorry – IP address won’t work at present
I never had to to write an IP
Running examples # cd mpjdev/test # javac -classpath ../lib/mpjdev.jar:.
BufferTest3.java # java -classpath ../lib/mpjdev.jar:.
BufferTest3 0 (O is the Rank)
Tracking problems java –version, is it 1.5. ? Are you using IP ? Email me
Writing your own programs As an example,
Two processes Initialize the device
CommImpl.init() Get your ID,
CommImpl.id() One process packs & sends data,
CommImpl.send(Buffer, int dest, int tag) Other process reads data & unpacks
CommImpl.recv(Buffer, int src, int tag) Finalize,
CommImpl.finish();
Sequence Introduction
History of MPJ Overview of java.nio package ‘mpjdev’ implementation
Introduction Packing/Unpacking at the device level Communication Protocols
Eager Send Rendezvous Protocol
Quick Start Guide to mpjdev What’s next
Neo: Why do my eyes hurt?Morpheus: You've never used them before.
A Few experiments No tests, yet Bottlenecks,
Transfer of huge messages seems inefficient Queues, java.util.Vector is not good enough
Would like to see how many processes, can selector handle ?
Potentially thousands Need bench-marks, keeping in view java
issues and bottlenecks, and test them Write our own
Future Badly need a runtime
Shell scripts starting jobs using ‘ssh’ or ‘rsh’ ?
MPJ, Group communications
I thought, I would have completed the whole MPJ, by now
Looking for my PhD project, in the same domain
Morpheus: Unfortunately, no one can be told what the Matrix is. You have tosee it for yourself.
Suggestions
?