Simulation with PsimJ2 and Java

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Simulation with PsimJ2 and Java

• Synchronous Cooperation

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Synchronous Cooperation

• Is carried out by two or more processes that
  execute a joint activity for a finite time
  interval.
• This involves the simultaneous participation of
  the processes
• One example is the modeling of direct
  communication among processes (inter-process
  communication).

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Master-Slave Synchronization

• In PsimJ2, one process is chosen as the master.
  This is the dominant process during the
  cooperation interval.
• The other processes are the slaves. These are
  modeled as passive participants during the
  interval of cooperation.
• When the cooperation ends, all processes continue
  with their own independent activities.

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Joint Activity

• For two processes to cooperate
• The master process requests a cooperation with a
  slave process to execute a joint activity.
• The slave process requests a cooperation with a
  master process in order to execute a joint
  activity

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Joint Activity Between Master and Slave
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Synchronized Wait in the Cooperation

• When the master process requests cooperation, and
  there is no slave process available, the master
  process has to wait
• If the master process has to wait, it is
  suspended and placed on the master queue
• When a slave process requests cooperation, and
  the master is not available, the slave process
  has to wait (suspended and placed on the slave
  queue)

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Synchronization Object

• The mechanism that implements this type of
  synchronization is defined in class Waitq.
• An object of this class is used as the passive
  object necessary for the synchronization of the
  processes (active objects) involved

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Master-Slave Cooperation
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Waitq Class in PsimJ2

• The cooperation mechanism is implemented in
  class Waitq
• The synchronization mechanism is controlled by an
  object of class Waitq.
• The relevant public members of class Waitq
• length(), for length of the slave queue
• lengthm(), for length of the master queue
• qwait(), called by slave processes
• coopt(), called by master processes

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Defining an Object of Class Waitq

• Declare and create an object of class Waitq
• Waitq coop_obj
• coop_obj new Waitq(Coop)

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Cooperation Requests

• Method coopt() is invoked by the master process.
  For example,
• sl_obj (Slave ) coop_obj.coopt() // get ref
  to slave
• The call is invoked on object coop_obj.

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Cooperation Requests

• Method qwait() is invoked by the slave process.
  For example,
• coop_obj.qwait() // request cooperation

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Deciding to Cooperate

• As with other classes in PsimJ2, a process may
  decide not to cooperate if there are no slave
  processes in the slave queue
• if(coop_obj.length() gt 0) // slaves available?
• sl_obj (Slave) waitq_obj.coopt()
• // joint activity with slave process
• else
• // perform some other activity

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Model with Synchronous Communication

• There are several sender processes
• There are several receiver processes
• A channel connects a receiver process to a sender
  process.
• A sender process directly communicates to with a
  receiver process in order to transfer a message.

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Model Implementation

• The sender processes are objects of class Sender
• The receiver processes are objects of class
  Receiver
• The channels are passive objects of class Comchan
  that include a reference to class Waitq
• The model is stored in file scomm.jar.

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Results of a Simulation Run

• Trace that shows sequence of events the times
  that a pair of processes communicate
• Total wait period for each receiver process
• Total wait period for each sender process
• Channel utilization

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Synchronous Communication Between Two Processes
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Multiple Slave Processes

• A single master process may need to cooperate
  with several slave processes simultaneously
  during cooperation interval
• A simple solution is for the master process to
  place every slave process in a queue until the
  end of the cooperation interval

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Java Implementation for Several Slave Processes
int slave 1 // current number of slave
processes Squeue s_queue new Squeue(Slaves)
while ( slave lt NUM_SLAVES ) slave_ref
(Slave) waitq_obj.coopt() s_queue.into(slave_r
ef) // place slave process in s_queue
slave // perform the joint activity //
dequeue and reactivate the slave processes