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<p style="margin-top:0;margin-bottom:0">I have found an issue with the use of Thread_Init object, the following code does not work:<br>
</p>
<p style="margin-top:0;margin-bottom:0"><i><br>
</i></p>
<p style="margin-top:0;margin-bottom:0"><span style="font-size:12pt;" id="divtagdefaultwrapper"></p>
<div><i>#pragma omp parallel</i></div>
<i></i>
<div><i>{</i></div>
<i></i>
<div><i> PPL::Thread_Init thread_init;<br>
</i></div>
<i></i>
<div><i>#pragma omp for<br>
for(int i=0; i<1000; i++){<br>
PPL::C_Polyhedron ph1(3); <br>
PPL::C_Polyhedron ph2(3);<br>
ph1.intersection_assign(ph2);<br>
}</i></div>
<i></i>
<div><i>}</i></div>
<div><span style="font-size:12pt;" id="divtagdefaultwrapper"><i>PPL::C_Polyhedron ph3(3); // => Segment fault</i><i></i></span></div>
<div><span style="font-size:12pt;" id="divtagdefaultwrapper"><br>
</span></div>
<div><span style="font-size:12pt;" id="divtagdefaultwrapper">It seems that when all the thread_init variables are delete, it is then impossible to instantiate or proceed to any operation with ppl.</span></div>
<div><span style="font-size:12pt;" id="divtagdefaultwrapper">A workaround is to instantiate a new Thread_Init variable but this is a bit heavy.</span></div>
<div><span style="font-size:12pt;" id="divtagdefaultwrapper"><br>
</span></div>
<div><span style="font-size:12pt;" id="divtagdefaultwrapper"><span style="font-size:12pt;" id="divtagdefaultwrapper">
<div><i>#pragma omp parallel</i></div>
<i></i>
<div><i>{</i></div>
<i></i>
<div><i> PPL::Thread_Init thread_init;<br>
</i></div>
<i></i>
<div><i>#pragma omp for<br>
for(int i=0; i<1000; i++){<br>
PPL::C_Polyhedron ph1(3); <br>
PPL::C_Polyhedron ph2(3);<br>
ph1.intersection_assign(ph2);<br>
}</i></div>
<i></i>
<div><i>}</i></div>
<div><i><span style="font-size:12pt;" id="divtagdefaultwrapper"><span style="font-size:12pt;" id="divtagdefaultwrapper"><span style="font-size:12pt;" id="divtagdefaultwrapper">PPL::Thread_Init thread_init;</span></span></span><br>
</i></div>
<div><span style="font-size:12pt;" id="divtagdefaultwrapper"><i>PPL::C_Polyhedron ph3(3); // => OK</i></span></div>
<div><span style="font-size:12pt;" id="divtagdefaultwrapper"><br>
</span></div>
<div><span style="font-size:12pt;" id="divtagdefaultwrapper">Any other idea?</span></div>
<div><span style="font-size:12pt;" id="divtagdefaultwrapper"><br>
</span></div>
<div><span style="font-size:12pt;" id="divtagdefaultwrapper">Thomas</span><span style="font-size:12pt;" id="divtagdefaultwrapper"></span><br>
<span style="font-size:12pt;" id="divtagdefaultwrapper"></span></div>
</span></span></div>
</span><br>
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<div id="divRplyFwdMsg" dir="ltr"><font face="Calibri, sans-serif" style="font-size:11pt" color="#000000"><b>De :</b> Thomas LE MÉZO<br>
<b>Envoyé :</b> mercredi 3 janvier 2018 12:26:09<br>
<b>À :</b> enea.zaffanella@unipr.it<br>
<b>Cc :</b> The Parma Polyhedra Library developers' list<br>
<b>Objet :</b> RE: [PPL-devel] OpenMP & PPL</font>
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<p style="margin-top:0; margin-bottom:0">It seems to work! To avoid multiple instantiation of
<span>thread_init</span>, a solution is to break down the "omp parallel for" in two lines:<br>
</p>
<p style="margin-top:0; margin-bottom:0"><br>
</p>
<p style="margin-top:0; margin-bottom:0"></p>
<div>#pragma omp parallel</div>
<div>{</div>
<div><span> PPL::Thread_Init thread_init;</span><br>
</div>
<div>#pragma omp for<br>
for(int i=0; i<1000; i++){<br>
<span><span>PPL</span></span>::C_Polyhedron ph1(3); <span></span><br>
<span><span>PPL</span></span>::C_Polyhedron ph2(3);<br>
ph1.intersection_assign(ph2);<br>
}</div>
<div>}<br>
</div>
<br>
<p></p>
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Thank you very much,</div>
<div dir="ltr" style="font-size:12pt; color:rgb(0,0,0); font-family:Calibri,Helvetica,sans-serif,"EmojiFont","Apple Color Emoji","Segoe UI Emoji",NotoColorEmoji,"Segoe UI Symbol","Android Emoji",EmojiSymbols">
Thomas<br>
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<br>
<br>
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<div id="x_divRplyFwdMsg" dir="ltr"><font color="#000000" face="Calibri, sans-serif" style="font-size:11pt"><b>De :</b> Enea Zaffanella <zaffanella.enea@gmail.com> de la part de Enea Zaffanella <zaffanella@cs.unipr.it><br>
<b>Envoyé :</b> mercredi 3 janvier 2018 11h17<br>
<b>À :</b> The Parma Polyhedra Library developers' list; Thomas LE MÉZO<br>
<b>Objet :</b> Re: [PPL-devel] OpenMP & PPL</font>
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<p><br>
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<br>
<div class="x_x_moz-cite-prefix">On 31/12/2017 17:33, Thomas LE MÉZO wrote:<br>
</div>
<blockquote type="cite">
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<p style="margin-top:0; margin-bottom:0">Dear <span>Enea, Dear all,</span></p>
<p style="margin-top:0; margin-bottom:0"><span><br>
</span></p>
<p style="margin-top:0; margin-bottom:0"><span>I tried recently to implement a multi-thread version of my thesis code using PPL library. I used OpenMP and the last version of ppl on devel git branch as I read you have been working on a thread-safe implementation
(thread-safe option with configure). I didn't succeed in writing a correct program; see for instance this simple code that return a segmentation fault :</span></p>
<p style="margin-top:0; margin-bottom:0"><span><br>
</span></p>
<p style="margin-top:0; margin-bottom:0"><span><span>#include <omp.h></span><br>
</span></p>
<p style="margin-top:0; margin-bottom:0"><span><span>namespace PPL = Parma_Polyhedra_Library;</span><br>
</span></p>
<p style="margin-top:0; margin-bottom:0"><span><br>
</span></p>
<p style="margin-top:0; margin-bottom:0"><span><span>int main(){</span><br>
</span></p>
<p style="margin-top:0; margin-bottom:0"><span></span></p>
<div>#pragma omp parallel for<br>
for(int i=0; i<1000; i++){<br>
<span><span>PPL</span></span>::C_Polyhedron ph1(3); // => segmentation fault
<span>at line 83 of Linear_Expression.cc</span><br>
<span><span>PPL</span></span>::C_Polyhedron ph2(3);<br>
ph1.intersection_assign(ph2);<br>
}</div>
<div> return 0;</div>
<div>}<br>
</div>
<br>
<p style="margin-top:0; margin-bottom:0">Would you have any idea about what is wrong?</p>
</div>
</blockquote>
<br>
Each thread should be properly initialized by creating a PPL::Thread_Init object (and finalized by destroying it).<br>
See for instance test01() in tests/Polyhedron/threadsafe1.cc<br>
As an alternative, you could use the make_threadable wrapper (see test02() in the same test).<br>
<br>
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<p style="margin-top:0; margin-bottom:0">Is PPL compatible with using OpenMP?</p>
</div>
</blockquote>
<br>
I never tried using it with OpenMP ... however, as long as thread initializations (and finalizations) are performed as suggested above, things should be working (there is also a library initialization part, but that is automatically done when working in C++).<br>
<br>
In you code, I would try adding<br>
<br>
PPL::Thread_Init thread_init;<br>
<br>
as the very first line of the loop body.<br>
This would maybe create more init objects than needed,<br>
but (if I remember correctly) that should not be a problem.<br>
<br>
Let us know how it goes.<br>
<br>
Enea<br>
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</p>
<p style="margin-top:0; margin-bottom:0">Thanks a lot in advance,</p>
<p style="margin-top:0; margin-bottom:0">Thomas<br>
</p>
<br>
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