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PVM Components and Terminology

System components

• pvmd3 daemon
  • Runs on each host

  • Provides inter-host point of contact

  • Provides authentication of tasks

  • Executes processes on host

  • Provides fault tolerance

  • Message routing and source and sink for messages

• libpvm programming library
  • Contains the message passing routines and is linked to each application component

• application components
  • User's programs, containing message passing calls, which are executed as PVM tasks

PVM Terminology

• Host
  • A physical machine such as a workstation

• Virtual Machine
  • A combination of hosts running as a single concurrent resource

• Process
  • A program, data, stack, etc such as a Unix process or node program

• Task
  • A PVM process - the smallest unit of computation

• TID
  • A unique identifier, within the virtual machine, which is associated with each task

• Message
  • An ordered list of data to be sent between tasks

Message Passing

Send and receive

• Sending a message is a 3 step process
  • Initialize a buffer using the pvmfinitsend function

  • Pack the data into the buffer using pvmfpack

  • Send the contents of the buffer to another process using pvmfsend or to a number of processes (multi-cast) using pvmfmcast

• Receiving a message is a 2 step process
  • Call the blocking routine pvmfrecv or the non-blocking routine pvmfnrecv

  • Unpack the message using pvmfunpack

Message Buffers

• PVM permits a user to manage multiple buffers but
  • there is only one active send and one active receive buffer per process at any given moment

  • the packing, sending, receiving and unpacking routines only affect active buffers

  • the developer may switch between multiple buffers for message passing

Packing Data

• In C PVM supports a number of different routines for packing data this corresponds to the different types of data to be packed

• PVM only provides one FORTRAN routine (pvmfpack) for packing data. pvmfpack handles all data types