[Mpi3-tools] Current Version of the MPIR document

[Ashley Pittman]

On 28 Jun 2010, at 22:35, John DelSignore wrote:
>> Like the original work this document specifies a definition for MPIR_PROCDESC, it however then goes on to say that the definition isn't fixed but rather is up to the implementation.
>> 
>> typedef struct {
>>  char *host_name;
>>  char *executable_name;
>>  int pid;
>> } MPIR_PROCDESC;
>> 
>> Section 9.2 paragraph 4:
>> The pid member is the integer process identifier of the MPI process. Note that historically pid was defined as a C language int, which is an integer of an unknown size, which might be smaller than the size of a process identifier for the target system. Implementations should define pid as an integer size that is large enough to hold a process identifier for the target system. For example, implementations should use pid_t as the type of pid provided that pid_t is an integer type.
> 
> I believe that that paragraph is accurate. The intent of MPIR has always been that the layout and sizes of the fields in MPIR_PROCDESC and the size of MPIR_PROCDESC itself are communicated through the debug information, and that the offsets and sizes were not hard-coded into the debugger. It was done this way for portability and to allow MPI implementations to rearrange the fields or toss extra fields into the structure.

I have to disagree based on the contents of the original header file.  This information is repeated on the ANL webpage where the header file is hosted, apologies for formatting here:

http://www.mcs.anl.gov/research/projects/mpi/mpi-debug/attach.h.html

/* A little struct to hold the target processor name and pid for
 * each process which forms part of the MPI program.
 * We may need to think more about this once we have dynamic processes...
 *
 * DO NOT change the name of this structure or its fields. The debugger knows
 * them, and will be confused if you change them.
 */

typedef struct
 {
  char * host_name;           
/* Something we can pass to inet_addr */

  char * executable_name;     
/* The name of the image */

  int    pid;		      
/* The pid of the process */

} MPIR_PROCDESC;

http://www.mcs.anl.gov/research/projects/mpi/mpi-debug/

MPIR_proctable
This is an array of structures with type
typedef struct {
  char * host_name;           /* Something we can pass to inet_addr */
  char * executable_name;     /* The name of the image */
  int    pid;		      /* The pid of the process */
} MPIR_PROCDESC;

>> Are there MPI librarys in existence which don't use int as the type for pid?
> 
> I don't know, but I'd guess there could be. I have some vague recollection that on Cray Catamount, pids were 64-bit and MPI was supported, so it's likely that MPI used 64-bit pids. Also, I think that IRIX has 64-bit pids, but SGI MPI didn't use the MPIR interface, they used "array services".
> 
>> I've certainly not seen any and never seen it necessary to read the type of MPIR_PROCDESC because it's type is well specified.
> 
> Just because you haven't seen any doesn't mean that they don't exist. You've been cheating and getting away with it.

Obviously the rest of my argument rests on the initial premise being true.

Ashley,

-- 

Ashley Pittman, Bath, UK.

Padb - A parallel job inspection tool for cluster computing
http://padb.pittman.org.uk