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<p class="MsoNormal"><span style="font-family:"Lucida Grande",sans-serif">Jim,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Lucida Grande",sans-serif"> I don’t fully understand your question. Is it “If all processes reach MPI_Barrier, are they guaranteed to exit the barrier without the need for any other MPI function to be called
on any process?” I would say yes.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Lucida Grande",sans-serif"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Lucida Grande",sans-serif">Rajeev<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Lucida Grande",sans-serif"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Lucida Grande",sans-serif"><o:p> </o:p></span></p>
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<p class="MsoNormal"><b><span style="font-size:12.0pt;color:black">From: </span></b><span style="font-size:12.0pt;color:black">mpi-forum <mpi-forum-bounces@lists.mpi-forum.org> on behalf of Jim Dinan via mpi-forum <mpi-forum@lists.mpi-forum.org><br>
<b>Reply-To: </b>Main MPI Forum mailing list <mpi-forum@lists.mpi-forum.org><br>
<b>Date: </b>Saturday, October 10, 2020 at 12:31 PM<br>
<b>To: </b>Main MPI Forum mailing list <mpi-forum@lists.mpi-forum.org><br>
<b>Cc: </b>Jim Dinan <james.dinan@gmail.com><br>
<b>Subject: </b>[Mpi-forum] Progress Question<o:p></o:p></span></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">Hi All,<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">A colleague recently asked a question that I wasn't able to answer definitively. Is the following code guaranteed to make progress?<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">MPI_Barrier();<o:p></o:p></p>
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<p class="MsoNormal">if rank == 1<o:p></o:p></p>
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<p class="MsoNormal"> create_file("test")<o:p></o:p></p>
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<p class="MsoNormal">if rank == 0<o:p></o:p></p>
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<p class="MsoNormal"> while not_exists("test")<o:p></o:p></p>
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<p class="MsoNormal"> sleep(1);<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">That is, can rank 1 require rank 0 to make MPI calls after its return from the barrier, in order for rank 1 to complete the barrier? If the code were written as follows:<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">isend(..., other_rank, &req[0])<o:p></o:p></p>
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<p class="MsoNormal">irecv(..., other_rank, &req[1])<o:p></o:p></p>
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<p class="MsoNormal">waitall(2, req)<o:p></o:p></p>
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<p class="MsoNormal">if rank == 1<o:p></o:p></p>
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<p class="MsoNormal"> create_file("test")<o:p></o:p></p>
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<p class="MsoNormal">if rank == 0<o:p></o:p></p>
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<p class="MsoNormal"> while not_exists("test")<o:p></o:p></p>
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<p class="MsoNormal"> sleep(1);<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">I think it would clearly not guarantee progress since the send data can be buffered. Is the same true for barrier?<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">Cheers,<o:p></o:p></p>
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<p class="MsoNormal"> ~Jim.<o:p></o:p></p>
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