x.html#Concept-Index" title="Index" rel="index">Index</a>]</p>
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<h3 class="section">6.9 Avoiding MPI Deadlocks</h3>
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<p>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&rsquo;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>s