[Mpi-comments] (A) Typo and (B) mal-correction in all MPI_Wait.../Test... descriptions
Rolf Rabenseifner
rabenseifner at hlrs.de
Fri Jun 8 10:42:01 CDT 2018
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) .
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