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Add FFTW3
author Chris Cannam <cannam@all-day-breakfast.com>
date Wed, 20 Mar 2013 15:35:50 +0000
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+<html lang="en">
+<head>
+<title>Avoiding MPI Deadlocks - FFTW 3.3.3</title>
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+<link rel="up" href="Distributed_002dmemory-FFTW-with-MPI.html#Distributed_002dmemory-FFTW-with-MPI" title="Distributed-memory FFTW with MPI">
+<link rel="prev" href="FFTW-MPI-Wisdom.html#FFTW-MPI-Wisdom" title="FFTW MPI Wisdom">
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+Copyright (C) 2003 Matteo Frigo.
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+<div class="node">
+<a name="Avoiding-MPI-Deadlocks"></a>
+<p>
+Next:&nbsp;<a rel="next" accesskey="n" href="FFTW-MPI-Performance-Tips.html#FFTW-MPI-Performance-Tips">FFTW MPI Performance Tips</a>,
+Previous:&nbsp;<a rel="previous" accesskey="p" href="FFTW-MPI-Wisdom.html#FFTW-MPI-Wisdom">FFTW MPI Wisdom</a>,
+Up:&nbsp;<a rel="up" accesskey="u" href="Distributed_002dmemory-FFTW-with-MPI.html#Distributed_002dmemory-FFTW-with-MPI">Distributed-memory FFTW with MPI</a>
+<hr>
+</div>
+
+<h3 class="section">6.9 Avoiding MPI Deadlocks</h3>
+
+<p><a name="index-deadlock-417"></a>
+An MPI program can <em>deadlock</em> if one process is waiting for a
+message from another process that never gets sent.  To avoid deadlocks
+when using FFTW's MPI routines, it is important to know which
+functions are <em>collective</em>: that is, which functions must
+<em>always</em> be called in the <em>same order</em> from <em>every</em>
+process in a given communicator.  (For example, <code>MPI_Barrier</code> is
+the canonical example of a collective function in the MPI standard.) 
+<a name="index-collective-function-418"></a><a name="index-MPI_005fBarrier-419"></a>
+
+   <p>The functions in FFTW that are <em>always</em> collective are: every
+function beginning with &lsquo;<samp><span class="samp">fftw_mpi_plan</span></samp>&rsquo;, as well as
+<code>fftw_mpi_broadcast_wisdom</code> and <code>fftw_mpi_gather_wisdom</code>. 
+Also, the following functions from the ordinary FFTW interface are
+collective when they are applied to a plan created by an
+&lsquo;<samp><span class="samp">fftw_mpi_plan</span></samp>&rsquo; function: <code>fftw_execute</code>,
+<code>fftw_destroy_plan</code>, and <code>fftw_flops</code>. 
+<a name="index-fftw_005fexecute-420"></a><a name="index-fftw_005fdestroy_005fplan-421"></a><a name="index-fftw_005fflops-422"></a>
+<!--  -->
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