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<p class="MsoNormal"><span style="font-family:"Lucida Grande",sans-serif">Does it mean that in the following program, although all processes have called barrier, some process may not exit the barrier for 100 days?<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">MPI_Init<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Lucida Grande",sans-serif">MPI_Barrier<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Lucida Grande",sans-serif">sleep(100 days)<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Lucida Grande",sans-serif">MPI_Finalize<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">Jim Dinan <james.dinan@gmail.com><br>
<b>Date: </b>Sunday, October 11, 2020 at 10:31 AM<br>
<b>To: </b>"Thakur, Rajeev" <thakur@anl.gov><br>
<b>Cc: </b>Main MPI Forum mailing list <mpi-forum@lists.mpi-forum.org><br>
<b>Subject: </b>Re: [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 Rajeev,<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">Yes, that's the question and my initial answer was the same as yours. However, we then started talking about the implementation of the barrier, which led to the second example. For example, consider a situation where there is an error in
transmission and the implementation needs to enter the progress engine to retry a send operation in software.<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal"> ~Jim.<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">On Sat, Oct 10, 2020 at 5:10 PM Thakur, Rajeev <<a href="mailto:thakur@anl.gov">thakur@anl.gov</a>> wrote:<o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-family:"Lucida Grande",sans-serif">Jim,</span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><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.</span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-family:"Lucida Grande",sans-serif"> </span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-family:"Lucida Grande",sans-serif">Rajeev</span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-family:"Lucida Grande",sans-serif"> </span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-family:"Lucida Grande",sans-serif"> </span><o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><b><span style="font-size:12.0pt;color:black">From:
</span></b><span style="font-size:12.0pt;color:black">mpi-forum <<a href="mailto:mpi-forum-bounces@lists.mpi-forum.org" target="_blank">mpi-forum-bounces@lists.mpi-forum.org</a>> on behalf of Jim Dinan via mpi-forum <<a href="mailto:mpi-forum@lists.mpi-forum.org" target="_blank">mpi-forum@lists.mpi-forum.org</a>><br>
<b>Reply-To: </b>Main MPI Forum mailing list <<a href="mailto:mpi-forum@lists.mpi-forum.org" target="_blank">mpi-forum@lists.mpi-forum.org</a>><br>
<b>Date: </b>Saturday, October 10, 2020 at 12:31 PM<br>
<b>To: </b>Main MPI Forum mailing list <<a href="mailto:mpi-forum@lists.mpi-forum.org" target="_blank">mpi-forum@lists.mpi-forum.org</a>><br>
<b>Cc: </b>Jim Dinan <<a href="mailto:james.dinan@gmail.com" target="_blank">james.dinan@gmail.com</a>><br>
<b>Subject: </b>[Mpi-forum] Progress Question</span><o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"> <o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto">Hi All,<o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"> <o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto">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" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"> <o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto">MPI_Barrier();<o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto">if rank == 1<o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"> create_file("test")<o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto">if rank == 0<o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"> while not_exists("test")<o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"> sleep(1);<o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"> <o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto">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" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"> <o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto">isend(..., other_rank, &req[0])<o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto">irecv(..., other_rank, &req[1])<o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto">waitall(2, req)<o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto">if rank == 1<o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"> create_file("test")<o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto">if rank == 0<o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"> while not_exists("test")<o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"> sleep(1);<o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"> <o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto">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" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"> <o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto">Cheers,<o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"> ~Jim.<o:p></o:p></p>
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