JCSP Tutorial

1
JCSP Tutorial Homework Hints

• COP 6614, Fall 2005

2
JCSP Tutorial

• The JCSP Library
• JCSP Processes
• Channels Interfaces
• Alting Channels Event Selection
• The Parallel Construct
• Putting It Together A Simple Example

3
The JCSP Library

• Developed by Peter Welch and Paul Austin
• Download Here
• http//www.cs.kent.ac.uk/projects/ofa/jcsp/
• Include the JCSP library in your project with
• import jcsp.lang.

4
JCSP Processes

• The process is the basic construct in JCSP
• Simply a class that implements the CSProcess
  interface.
• Ex
• public class MyProcess implements CSProcess
• public void run()

5
Channels Interfaces (1)

• Processes are wired together using channels.
• ChannelInput interface
• Interface for reading from a channel
• Consists of single method called read
• If called on an object, it will block until an
  object is actually written on the channel by a
  process at the other end of the channel.
• ChannelOutput interface
• Interface for writing from a channel
• Consists of a single method called write(Object
  o).
• A process that calls this method on an object
  will block until the object is accepted by the
  channel.

6
Channels Interfaces (2)

• Types of channel classes
• One2OneChannel ? implements a "single-writer-singl
  e-reader" type channel
• One2AnyChannel ?implements a "single-writer-multip
  le-readers" object channel. (Note This is not a
  broadcast mechanism in that the multiple readers
  actually compete with each other for reading from
  the channel only one reader can use the channel
  along with the writer at any given time.)
• Any2OneChannel ? implements a "multiple-writers-si
  ngle-reader" object channel. As in the above
  case, writing processes compete with each other
  to use the channel. Only the reader and one of
  the multiple writers can actually use the channel
  at any given time
• Any2AnyChannel ?implements a "multiple-writers-mul
  tiple-readers" object channel. Reading processes
  compete with each other to use the channel, as do
  writing processes. Only one reader and one writer
  can actually use the channel at any one time.

7
Channels Interfaces (3)

• Channels are non buffering by default, but JCSP
  supports buffering.
• Buffering is delegated to another class, which
  must implement an interface called
  ChannelDataStore. JCSP provides multiple built-in
  implementations for this interface, including the
  following
• ZeroBuffer default non buffering channel
• Buffer provides a blocking FIFO buffered
  semantics for the channel with which it is
  associated.
• InfiniteBuffer provides a FIFO semantics,
  except that only readers can be blocked if the
  buffer is empty. Writers are never blocked
  because the buffer capacity can be expanded
  indefinitely, or at least until the limit imposed
  by the underlying memory system is reached.

8
Alting Channels Event Selection

• A channel guard in JCSP can be of the following
  types AltingChannelInput / AltingChannelInputInt,
  which are ready whenever object/integer data
  (respectively) is pending in the corresponding
  channel The Alternative class provides methods
  for event-selection
• The method select() of the Alternative class
  corresponds to an arbitrary selection strategy.
• The method priSelect() corresponds to the highest
  priority strategy.
• The method fairSelect is fair in choosing between
  the more-than-one ready guards

9
The Parallel Construct

• Takes an array of individual CSProcess instances
  and runs them in parallel.
• A run of a Parallel process terminates when, and
  only when, all its component processes terminate.
  
• A mechanism for composing multiple individual
  processes together, using channels as "wires" to
  connect them.
• Example
• new Parallel
• (
• new CSProcess
• new SendEvenIntsProcess (chan),
• new ReadEvenIntsProcess (chan)
• ).run ()

10
Putting It All TogetherA Simple Example (1)

• Consider a simple process that produces the
  integers from 1 to 100 and another process which
  consumes them.
• Need 3 Processes
• Producer Process
• Consumer Process
• Driver Process to instantiate and start the
  producer and consumer processes.
• Producer and Consumer are wired together using
  ChannelInput and ChannelOutput interfaces.

11
Putting It All TogetherA Simple Example (2)
Int Producer Process
Int Consumer Process
Channel
Channel Input
Channel Output
12
Putting It All TogetherA Simple Example (3)

• Producer process to generate even integers
  between 1 and 100
• import jcsp.lang.
• public class SendEvenIntsProcess implements
  CSProcess
• private ChannelOutput out
• public SendEvenIntsProcess(ChannelOutput out)
• this.out out
• public void run()
• for (int i 2 i lt 100 i i 2)
• out.write (new Integer (i))

13
Putting It All TogetherA Simple Example (4)

• Consumer process to read even integers between 1
  and 100
• import jcsp.lang.
• public class ReadEvenIntsProcess implements
  CSProcess
• private ChannelInput in
• public ReadEvenIntsProcess(ChannelInput in)
• this.in in
• public void run()
• while (true)
• Integer d (Integer)in.read()
• System.out.println("Read "
  d.intValue())

14
Putting It All TogetherA Simple Example (5)

• The Driver Program
• import jcsp.lang.
• public class DriverProgram
• public static void main(String args)
• One2OneChannel chan new One2OneChannel()
• new Parallel
• (
• new CSProcess
• new SendEvenIntsProcess (chan),
• new ReadEvenIntsProcess (chan)
• ).run ()

15
Homework Hints (problem 1)Producer / Consumer

• The Producer process takes in the number of
  items and the speed at which it will produce an
  item as parameters.
• The Buffer process implements a circular queue of
  size 20. Once the Buffer process detects that the
  queue has been emptied, it will send a signal to
  the two consumers to indicate that the buffer is
  empty.
• The two Consumers will run at different speeds as
  defined by a parameter passed to it . The two
  consumers should then terminate normally when the
  Buffer process informs that there are no more
  items to consume.

16
Homework Hints (problem 1)Producer / Consumer

• 4 Processes
• 1 driver process (i.e. main)
• Producer process
• Consumer process
• Buffer Process

17
Homework Hints (problem 1)Producer / Consumer
Consumer1 receives items from the
buffer One2OneChannelInt chanConToBuff1 One2OneCha
nnelInt chanConFromBuff1

• Define Channels

NOTE Buffer / Consumer channels are
Bidirectional. Consumers send request To buffer
when wanting ton consume. Buffer will send item
to consumer if requesting Items are available
in the buffer.
Producer sends items (ints) to the
buffer One2OneChannelInt chanProdBuff
Consumer2 receives items from the
buffer One2OneChannelInt chanConToBuff2 One2OneCha
nnelInt chanConFromBuff2
Note Buffer has potential to receive multiple
events (receiving an item from a consumer and
message that data is available from the producer.
Need event selection (i.e. Alting Channel).
18
Homework Hints (problem 1)Producer / Consumer

• Producer Process
• public class Producer implements CSProcess
• public Producer(int numItems, int interval,
  One2OneChannelInt toBuffer)
• Create an int and send it to the buffer using
  toBuffer.write(i)
• Consumer Process
• public class Consumer implements CSProcess
• public Consumer(String str, int interval,
  ChannelOutputInt toBuffer, One2OneChannelInt
  fromBuffer)
• signal the buffer we are ready to consume using
  toBuffer.write(MORE)
• read the data from the channel int item
  fromBuffer.read()

19
Homework Hints (problem 1)Producer / Consumer

• Driver Process
• Instantiate channels
• One2OneChannelInt ProdBuff new
  One2OneChannelInt()
• One2OneChannelInt ConBuff1 new
  One2OneChannelInt()
• One2OneChannelInt ConBuff2 new
  One2OneChannelInt()
• Instantiate producer, consumer, buffer processes
• Example Consumer consumer1 new Consumer(100,
  ConToBuff1,ConFromBuff1)
• Start processes running in parallel
• Example new Parallel ( new CSProcess
  buffer,producer,consumer1, consumer2 ).run()

20
Homework Hints (problem 2)Optimal Algorithm

• Ricart-Agrawal Algorithm Implement the Optimal
  Algorithm for Mutual Exclusion for Computer
  Networks as given by Ricart-Agrawal (the paper
  was presented in class). The link for the paper
  can be found in the reading list.
• The number of nodes in the network (N) will be
  passed as parameter.
• Note Use message passing to resolve all
  synchronizations. (Do not use semaphores).

21
Homework Hints (problem 2)Optimal Algorithm

• Reviewing The Algorithm (1)

22
Homework Hints (problem 2)Optimal Algorithm

• Reviewing The Algorithm (1)

23
Homework Hints (problem 2)Optimal Algorithm

• Reviewing The Algorithm (3)

24
Homework Hints (problem 2)Optimal Algorithm

• Parallel Inside Of Parallel Architecture
• Node Processes consist of 3 Sub Processes
• Mutex Process invokes mutual exclusion for the
  node
• Request Process process that receives request
  messages
• Reply Process process that receives reply
  messages
• Node contained a database of shared variables
  between the 3 sub-processes must provide
  protected access to them via mutex.

25
Homework Hints (problem 2)Optimal Algorithm

• Channel Layout

Node (shared database)
Node (shared database)
26
Project 1 Due Date Oct 12

• ?