Notes 2020 05 14

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Marc-Andre Hermanns edited this page May 14, 2020 · 1 revision

Meeting 2020-05-14

Participants

John DelSignore
Bengisu Elis
Marc-Andre Hermanns
Joachim Protze
Martin Schulz

Topics

Handle Introspection

Discussion based on Wiki page here
- Started by copy-pasting Jeff S.'s interface present in OMPI
- Each debugging handle has a constructor and free function
  - Debugging handle is only valid until the execution continues
    - I.e., only while the application is stopped
  - Constructor takes a address of MPI handle
- How does the debugger know that a handle is a request
  - Purely by convention (checking the name of the type)
    - What if some non-MPI application uses the name MPI_Request for a type
  - It's an opaque handle and it is required to be comparable in the base language (need to look up the text)
    - Can only be a scalar
- Should the input the handle query be the opaque handle value or a pointer to the opaque handle?
Which queries are possible?
- Communicators
  - Basic query
    - Printable name
      - John discourages to use a string argument type like char name[MPI_MAX_OBJECT_NAME]
        
        Cannot be an implementation dependent size
      - Alternative would be library allocates and user frees memory
        
        Not used in the 1st-party MPI API
        
        Used by some libc calls
    - Rank & size
    - Fortran handle
    - Extra info as key-value pair
      - Similar to ICV in OpenMP
  - Procs
    - List of Processes that are part of the communicator
What is mpidbg_process_t ?
- ID of current process
  - in OMPI the world rank
How does the (multi-process) debugger communicate which MPI process is to be queried for a specific UNIX process
Where does a debugger get the context of the process