[Mpi-comments] (A) Typo and (B) mal-correction in all MPI_Wait.../Test... descriptions

[Rolf Rabenseifner]

Dear all,

A) Typo:

My colleague Martin Bernreuther detected the following typo:

MPI-3.1 Section "3.7.3 Communication Completion", "MPI_WAIT"
page 53, lines 24-25 read

"[...]. Any other type of request
is and the request handle is set to MPI_REQUEST_NULL. [...]"

but should read
"[...]. Any other type of request
is deallocated and the request handle is set to MPI_REQUEST_NULL. [...]"

In other Locations, this sentence is correct, i.e., includes the
word "deallocated", see MPI-3.1 
 - page 54, lines 20-21 in MPI_TEST, 
 - page 57, lines 45-46 in MPI_WAITANY,
 - page 58, lines 35-36 in MPI_TESTANY,
 - page 59, lines 23-24 in MPI_WAITALL,
 - page 60, lines 25-26 in MPI_TESTALL,
 - page 61, lines 19-20 in MPI_WAITSOME,
whereas MPI_TESTALL does not contain this sentence due
to a shorter description.


B) Mal-correction:

The correction from MPI-2.2 to MPI-3.0 contains wrong wording for 
MPI_Wait/Test... in the case of inactive request handles.

The correction was done to include also nonblocking collectives and IO.
But the change to MPI-3.0 was not correct for inactive persistent request handles.

MPI-1.1 - MPI-2.2 used the wording:

"A call to MPI WAIT returns when the operation identified by request is complete. 
If the communication object associated with this request was created by a nonblocking send or
receive call, then the object is deallocated by the call to MPI WAIT and the request handle
is set to MPI REQUEST NULL. 
MPI WAIT is a non-local operation.
The call returns, in status, [...].
One is allowed to call MPI WAIT with a null or inactive request argument. In this case
the operation returns immediately with empty status."

For inactive persistent request handles, the text says:
- no change for the request handle,
- empty status returned.

  
MPI-3.0 and MPI-3.1 uses the following modified wording:

"A call to MPI_WAIT returns when the operation identified by request is complete. 
If the request is an active persistent request, it is marked inactive. Any other type of request
is [deallocated] and the request handle is set to MPI_REQUEST_NULL. 
MPI_WAIT is a non-local operation.
The call returns, in status, [...].
One is allowed to call MPI_WAIT with a null or inactive request argument. In this case
the operation returns immediately with empty status."

For inactive persistent request handles, the text says:
- that it shpould be set to MPI_REQUEST_NULL, and
- empty status returned.

The MPI_REQUEST_NULL was never intented and I expect that no MPI-library 
has implemented that wrong behavior.
Note that in the case of an array of request handles, in a sequence of MPI_Wait/Test-any/some
calls, it is allowed to keep the whole array untouched until all regular requests
are set to MPI_REQUEST_NULL and all active persistent requests are changed to inactive.


Proposal for correcting thos bug:

Change all sentences

"Any other type of request
 is deallocated and the request handle is set to MPI_REQUEST_NULL."

into

"Any other type of non-persistent request
 is deallocated and the request handle is set to MPI_REQUEST_NULL."
 
The locations are:

 - page 53, lines 24-25 in MPI_WAIT (together with the typo, see (A) above)
 - page 54, lines 20-21 in MPI_TEST, 
 - page 57, lines 45-46 in MPI_WAITANY,
 - page 58, lines 35-36 in MPI_TESTANY,
 - page 59, lines 23-24 in MPI_WAITALL,
 - page 60, lines 25-26 in MPI_TESTALL,
 - page 61, lines 19-20 in MPI_WAITSOME.


Best regards
Rolf 


-- 
Dr. Rolf Rabenseifner . . . . . . . . . .. email rabenseifner at hlrs.de .
High Performance Computing Center (HLRS) . phone ++49(0)711/685-65530 .
University of Stuttgart . . . . . . . . .. fax ++49(0)711 / 685-65832 .
Head of Dpmt Parallel Computing . . . www.hlrs.de/people/rabenseifner .
Nobelstr. 19, D-70550 Stuttgart, Germany . . . . (Office: Room 1.307) .