Tags and Contexts

• Separation of messages used to be accomplished by use of tags, but

  • this requires libraries to be aware of tags used by other libraries.
  • this can be defeated by use of “wild card” tags.

• Contexts are different from tags

  • no wild cards allowed
  • allocated dynamically by the system when a library sets up a communicator for its own use.

• User-defined tags still provided in MPI for user convenience in organizing application

• Use MPI_Comm_split to create new communicators

Notes: