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First, are there folks who still maintain or need to work with legacy Fortran code that relies on
<code>include 'mpif.h</code> interface?</div>
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Our CI testing machine for Macos recently upgraded and left us (MPICH development) with some regression failures. The failures are from not recognizing special constants such as MPI_BOTTOM and MPI_IN_PLACE. These constants are implemented using
<code>COMMON BLOCK</code>. For those who are not familiar, COMMON BLOCK allows different FORTRAN objects to declare global variables and to be merged at link time. The upgraded
<code>dyld</code> on Mac refuse to do that between user code and <code>libmpifort.dylib</code>, resulting in constants such as
<code>MPI_IN_PLACE</code> not being recognized.<br>
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The better way of implementing global variables in Fortran is via the module interface. But what about those legacy codes that can't be updated?</div>
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Here are the options:</div>
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1. Figure out a way to make COMMON BLOCKS on modern Mac work – we need help!</div>
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2. Leave it as is - everything will work except legacy Fortran on MacOS. We add a note in the documentation and move on.</div>
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3. Suggest users to <code>use mpi</code> instead. But if that suggestion will always work, maybe we can put "use mpi" inside "mpif.h" – assuming that all Fortran compilers are able to support the module interface today even when users don't realize that.</div>
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The option 3 is what the subject line refers to. <br>
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Feedback?</div>
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Hui Zhou<br>
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