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Forwarding this from the MPI-comments list to the Fortran working group...
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<span style="font-family: -webkit-system-font, Helvetica Neue, Helvetica, sans-serif; color:rgba(0, 0, 0, 1.0);" class=""><b class="">From:
</b></span><span style="font-family: -webkit-system-font, Helvetica Neue, Helvetica, sans-serif;" class="">Gilles Gouaillardet <<a href="mailto:gilles@rist.or.jp" class="">gilles@rist.or.jp</a>><br class="">
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<span style="font-family: -webkit-system-font, Helvetica Neue, Helvetica, sans-serif; color:rgba(0, 0, 0, 1.0);" class=""><b class="">Subject:
</b></span><span style="font-family: -webkit-system-font, Helvetica Neue, Helvetica, sans-serif;" class=""><b class="">[Mpi-comments] MPI_Comm_spawn_multiple: parameter description and Fortran bindings</b><br class="">
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<span style="font-family: -webkit-system-font, Helvetica Neue, Helvetica, sans-serif; color:rgba(0, 0, 0, 1.0);" class=""><b class="">Date:
</b></span><span style="font-family: -webkit-system-font, Helvetica Neue, Helvetica, sans-serif;" class="">February 6, 2018 at 3:04:00 AM EST<br class="">
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<span style="font-family: -webkit-system-font, Helvetica Neue, Helvetica, sans-serif; color:rgba(0, 0, 0, 1.0);" class=""><b class="">Reply-To:
</b></span><span style="font-family: -webkit-system-font, Helvetica Neue, Helvetica, sans-serif;" class="">Comments on the MPI Standard <<a href="mailto:mpi-comments@lists.mpi-forum.org" class="">mpi-comments@lists.mpi-forum.org</a>><br class="">
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<div class="">Dear MPI Forum,<br class="">
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The description of the 'array_of_commands` parameter passed to 'MPI_Comm_spawn_multiple()' is not crystal clear IMHO.<br class="">
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The standard simply states<br class="">
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MPI_COMM_SPAWN_MULTIPLE(count, array_of_commands, ...)<br class="">
IN count number of commands (positive integer, significant to MPI<br class="">
only at root | see advice to users)<br class="">
IN array_of_commands programs to be executed (array of strings,<br class="">
significant only at root)<br class="">
<br class="">
Advice to users. The argument count is interpreted by MPI only at<br class="">
the root, as is<br class="">
array_of_argv. Since the leading dimension of array_of_argv is<br class="">
count, a non-positive<br class="">
value of count at a non-root node could theoretically cause a<br class="">
runtime bounds check<br class="">
error, even though array_of_argv should be ignored by the<br class="">
subroutine. If this happens,<br class="">
you should explicitly supply a reasonable value of count on the<br class="">
non-root nodes. (End<br class="">
of advice to users.)<br class="">
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And the Fortran binding is<br class="">
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MPI_COMM_SPAWN_MULTIPLE(COUNT, ARRAY_OF_COMMANDS, ...)<br class="">
INTEGER COUNT<br class="">
CHARACTER*(*) ARRAY_OF_COMMANDS(*)<br class="">
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Intuitively, it seems obvious that 'array_of_commands' is an array of 'count' commands.<br class="">
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That being said, the standard does not state that, and it is unclear whether 'array_of_commands' should be<br class="">
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NULL-terminated (so to speak) or not.<br class="">
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Back to the Fortran binding, the following prototype, which is somehow consistent with 'array_of_argv',<br class="">
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could (help to) clear the confusion. The same comments also apply to the Fortran 2008 binding.<br class="">
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CHARACTER*(*) ARRAY_OF_COMMANDS(COUNT)<br class="">
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<br class="">
<br class="">
Gilles<br class="">
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<a href="mailto:jsquyres@cisco.com" class="">jsquyres@cisco.com</a></div>
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