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<p>Thanks all for your very insightful answers. <br>
</p>
<p>We are leveraging PETSc from Julia in a parallel distributed
memory context (several MPI tasks running the Julia REPL each).</p>
<p>Julia uses Garbage Collection (GC), and we would like to destroy
the PETSc objects automatically when the GC decides so along the
simulation.<br>
</p>
<p>In this context, we cannot guarantee deterministic destruction on
all MPI tasks as the GC decisions are local to each task, no
global semantics guaranteed.</p>
<p> As far as I understand from your answers, there seems to be the
possibility to defer the destruction of objects till points in the
parallel program in which you can guarantee collective semantics,
correct? If yes I guess that this may occur at any point in the
simulation, not necessarily at shut down via PetscFinalize(),
right? <br>
</p>
<p>Best regards,</p>
<p> Alberto.<br>
</p>
<p> <br>
</p>
<div class="moz-cite-prefix">On 24/10/21 1:10 am, Jacob
Faibussowitsch wrote:<br>
</div>
<blockquote type="cite"
cite="mid:171199C7-42C9-4D5C-96FD-83F08CFA33A8@gmail.com">
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
Depending on the use-case you may also find
PetscObjectRegisterDestroy() useful. If you can’t guarantee your
PetscObjectDestroy() calls are collective, but have some other
collective section you may call it then to punt the destruction of
your object to PetscFinalize() which is guaranteed to be
collective.
<div class=""><br class="">
</div>
<div class=""><a
href="https://petsc.org/main/docs/manualpages/Sys/PetscObjectRegisterDestroy.html"
class="" moz-do-not-send="true">https://petsc.org/main/docs/manualpages/Sys/PetscObjectRegisterDestroy.html</a></div>
<div class=""><br class="">
<div class="">
<div dir="auto" style="caret-color: rgb(0, 0, 0); color:
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class="">
<div dir="auto" style="caret-color: rgb(0, 0, 0); color:
rgb(0, 0, 0); letter-spacing: normal; text-align: start;
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text-decoration: none; word-wrap: break-word;
-webkit-nbsp-mode: space; line-break: after-white-space;"
class="">
<div>Best regards,<br class="">
<br class="">
Jacob Faibussowitsch<br class="">
(Jacob Fai - booss - oh - vitch)<br class="">
</div>
</div>
</div>
</div>
<div><br class="">
<blockquote type="cite" class="">
<div class="">On Oct 22, 2021, at 23:33, Jed Brown <<a
href="mailto:jed@jedbrown.org" class=""
moz-do-not-send="true">jed@jedbrown.org</a>> wrote:</div>
<br class="Apple-interchange-newline">
<div class="">
<meta charset="UTF-8" class="">
<span style="caret-color: rgb(0, 0, 0); font-family:
Menlo-Regular; font-size: 11px; font-style: normal;
font-variant-caps: normal; font-weight: normal;
letter-spacing: normal; text-align: start; text-indent:
0px; text-transform: none; white-space: normal;
word-spacing: 0px; -webkit-text-stroke-width: 0px;
text-decoration: none; float: none; display: inline
!important;" class="">Junchao Zhang <</span><a
href="mailto:junchao.zhang@gmail.com"
style="font-family: Menlo-Regular; font-size: 11px;
font-style: normal; font-variant-caps: normal;
font-weight: normal; letter-spacing: normal; orphans:
auto; text-align: start; text-indent: 0px;
text-transform: none; white-space: normal; widows: auto;
word-spacing: 0px; -webkit-text-size-adjust: auto;
-webkit-text-stroke-width: 0px;" class=""
moz-do-not-send="true">junchao.zhang@gmail.com</a><span
style="caret-color: rgb(0, 0, 0); font-family:
Menlo-Regular; font-size: 11px; font-style: normal;
font-variant-caps: normal; font-weight: normal;
letter-spacing: normal; text-align: start; text-indent:
0px; text-transform: none; white-space: normal;
word-spacing: 0px; -webkit-text-stroke-width: 0px;
text-decoration: none; float: none; display: inline
!important;" class="">> writes:</span><br
style="caret-color: rgb(0, 0, 0); font-family:
Menlo-Regular; font-size: 11px; font-style: normal;
font-variant-caps: normal; font-weight: normal;
letter-spacing: normal; text-align: start; text-indent:
0px; text-transform: none; white-space: normal;
word-spacing: 0px; -webkit-text-stroke-width: 0px;
text-decoration: none;" class="">
<br style="caret-color: rgb(0, 0, 0); font-family:
Menlo-Regular; font-size: 11px; font-style: normal;
font-variant-caps: normal; font-weight: normal;
letter-spacing: normal; text-align: start; text-indent:
0px; text-transform: none; white-space: normal;
word-spacing: 0px; -webkit-text-stroke-width: 0px;
text-decoration: none;" class="">
<blockquote type="cite" style="font-family: Menlo-Regular;
font-size: 11px; font-style: normal; font-variant-caps:
normal; font-weight: normal; letter-spacing: normal;
orphans: auto; text-align: start; text-indent: 0px;
text-transform: none; white-space: normal; widows: auto;
word-spacing: 0px; -webkit-text-size-adjust: auto;
-webkit-text-stroke-width: 0px; text-decoration: none;"
class="">On Fri, Oct 22, 2021 at 9:13 PM Barry Smith
<<a href="mailto:bsmith@petsc.dev" class=""
moz-do-not-send="true">bsmith@petsc.dev</a>> wrote:<br
class="">
<br class="">
<blockquote type="cite" class=""><br class="">
One technical reason is that
PetscHeaderDestroy_Private() may call<br class="">
PetscCommDestroy() which may call MPI_Comm_free()
which is defined by the<br class="">
standard to be collective. Though PETSc tries to limit
its use of new MPI<br class="">
communicators (for example generally many objects
shared the same<br class="">
communicator) if we did not free those we no longer
need when destroying<br class="">
objects we could run out.<br class="">
<br class="">
</blockquote>
PetscCommDestroy() might call MPI_Comm_free() , but it
is very unlikely.<br class="">
Petsc uses reference counting on communicators, so in
PetscCommDestroy(),<br class="">
it likely just decreases the count. In other words,
PetscCommDestroy() is<br class="">
cheap and in effect not collective.<br class="">
</blockquote>
<br style="caret-color: rgb(0, 0, 0); font-family:
Menlo-Regular; font-size: 11px; font-style: normal;
font-variant-caps: normal; font-weight: normal;
letter-spacing: normal; text-align: start; text-indent:
0px; text-transform: none; white-space: normal;
word-spacing: 0px; -webkit-text-stroke-width: 0px;
text-decoration: none;" class="">
<span style="caret-color: rgb(0, 0, 0); font-family:
Menlo-Regular; font-size: 11px; font-style: normal;
font-variant-caps: normal; font-weight: normal;
letter-spacing: normal; text-align: start; text-indent:
0px; text-transform: none; white-space: normal;
word-spacing: 0px; -webkit-text-stroke-width: 0px;
text-decoration: none; float: none; display: inline
!important;" class="">Unless it's the last reference to
a given communicator, which is a risky/difficult thing
for a user to guarantee and the consequences are
potentially dire (deadlock being way worse than a crash)
when the user's intent is to relax ordering for
destruction.</span><br style="caret-color: rgb(0, 0, 0);
font-family: Menlo-Regular; font-size: 11px; font-style:
normal; font-variant-caps: normal; font-weight: normal;
letter-spacing: normal; text-align: start; text-indent:
0px; text-transform: none; white-space: normal;
word-spacing: 0px; -webkit-text-stroke-width: 0px;
text-decoration: none;" class="">
<br style="caret-color: rgb(0, 0, 0); font-family:
Menlo-Regular; font-size: 11px; font-style: normal;
font-variant-caps: normal; font-weight: normal;
letter-spacing: normal; text-align: start; text-indent:
0px; text-transform: none; white-space: normal;
word-spacing: 0px; -webkit-text-stroke-width: 0px;
text-decoration: none;" class="">
<span style="caret-color: rgb(0, 0, 0); font-family:
Menlo-Regular; font-size: 11px; font-style: normal;
font-variant-caps: normal; font-weight: normal;
letter-spacing: normal; text-align: start; text-indent:
0px; text-transform: none; white-space: normal;
word-spacing: 0px; -webkit-text-stroke-width: 0px;
text-decoration: none; float: none; display: inline
!important;" class="">Alberto, what is the use case in
which deterministic destruction is problematic? If you
relax it for individual objects, is there a place you
can be collective to collect any stale communicators?</span></div>
</blockquote>
</div>
<br class="">
</div>
</blockquote>
<pre class="moz-signature" cols="72">--
Alberto F. Martín-Huertas
Senior Researcher, PhD. Computational Science
Centre Internacional de Mètodes Numèrics a l'Enginyeria (CIMNE)
Parc Mediterrani de la Tecnologia, UPC
Esteve Terradas 5, Building C3, Office 215,
08860 Castelldefels (Barcelona, Spain)
Tel.: (+34) 9341 34223
<a class="moz-txt-link-abbreviated" href="mailto:e-mail:amartin@cimne.upc.edu">e-mail:amartin@cimne.upc.edu</a>
FEMPAR project co-founder
web: <a class="moz-txt-link-freetext" href="http://www.fempar.org">http://www.fempar.org</a>
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