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List: squeak-vm-dev
Subject: Re: [Vm-dev] [Cuis-dev] Crashes on snapshot with the new compactor
From: Juan Vuletich <JuanVuletich () zoho ! com>
Date: 2017-03-27 3:26:20
Message-ID: 58D8865C.6020506 () zoho ! com
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Hi Eliot,
Nobody has reported crashes on image save on Cuis. I never experienced
one. So, I guess it is ok to wait for the VM fix, as the extra GC as a
workaround doesn't seem needed in Cuis.
Thanks,
On 25/03/2017 05:27 p.m., Eliot Miranda via Cuis-dev wrote:
> Hi All,
>
> a number of people are being affected by crashes on snapshotting
> the image, the worst possible time for a crash. There is a bug in the
> new compactor that unfortunately bites when saving. The compactor is
> invoked as part of a full garbage collect after the garbage collector
> has feed unreachable objects. Normally the new compactor makes only a
> single pass through the heap, which may not move all the objects that
> are possible to move. (The amount of objects that can be moved in a
> single pass is limited by available free space.) But on snapshot the
> compactor makes as may passes as are necessary to slide all movable
> objects down as far as possible. Unfortunately there is a bug in this
> second pass.
>
> Fixing this bug is now my priority. I have an example image from
> Esteban Lorenzano to test. I am asking anyone else that can provide
> an image that reliably crashes when trying to save it to make the
> image and changes available to me for testing if possible.
>
> In the mean time one may be able to work around the problem by doing a
> full garbage collect before snapshot. This should do a GC with a
> single compaction pass which should not fail, and then make it much
> more likely that the GC during snapshot will do a single compaction
> pass, since fewer objects should be mobile after the single pass
> compaction in the explicit GC.
>
> To do this in Pharo I would put a full gc here:
>
> SessionManager>>snapshot: save andQuit: quit
> | isImageStarting snapshotResult |
> ChangesLog default logSnapshot: save andQuit: quit.
>
> >> SmalltalkImage current primitiveGarbageCollect.
>
> self currentSession stop: quit."Image not usable from here until the
> session is restarted!"
> ...
>
> In Squeak I would put a full GC here:
>
> snapshot: save andQuit: quit withExitCode: exitCode embedded: embeddedFlag
> "Mark the changes file and close all files as part of
> #processShutdownList.
> If save is true, save the current state of this Smalltalk in the image
> file.
> If quit is true, then exit to the outer OS shell.
> If exitCode is not nil, then use it as exit code.
> The latter part of this method runs when resuming a previously saved
> image. This resume logic checks for a document file to process when
> starting up."
>
> | resuming msg |
> Object flushDependents.
> Object flushEvents.
>
> ...
> Smalltalk processShutDownList: quit.
> >>SmalltalkImage current primitiveGarbageCollect.
> Cursor write show.
> save ifTrue: [resuming := embeddedFlag
> ifTrue: [self snapshotEmbeddedPrimitive]
> ifFalse: [self snapshotPrimitive]] "<-- PC frozen here on image file"
> ifFalse: [resuming := false].
>
> I do apologise for the bug. I hope it will be fixed within a few days.
>
> _,,,^..^,,,_
> best, Eliot
>
>
> _______________________________________________
> Cuis-dev mailing list
> Cuis-dev@cuis-smalltalk.org
> http://cuis-smalltalk.org/mailman/listinfo/cuis-dev_cuis-smalltalk.org
--
Juan Vuletich
www.cuis-smalltalk.org
https://github.com/Cuis-Smalltalk/Cuis-Smalltalk-Dev
@JuanVuletich
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Hi Eliot,<br>
<br>
Nobody has reported crashes on image save on Cuis. I never
experienced one. So, I guess it is ok to wait for the VM fix, as the
extra GC as a workaround doesn't seem needed in Cuis.<br>
<br>
Thanks,<br>
<br>
On 25/03/2017 05:27 p.m., Eliot Miranda via Cuis-dev wrote:
<blockquote
cite="mid:CAC20JE17h+ZNzagDh=xr+_st+D5YgPML2N+uLo_+pawqwWZ1Rw@mail.gmail.com"
type="cite">
<div dir="ltr">Hi All,
<div><br>
</div>
<div> a number of people are being affected by crashes on
snapshotting the image, the worst possible time for a crash.
There is a bug in the new compactor that unfortunately bites
when saving. The compactor is invoked as part of a full
garbage collect after the garbage collector has feed
unreachable objects. Normally the new compactor makes only a
single pass through the heap, which may not move all the
objects that are possible to move. (The amount of objects
that can be moved in a single pass is limited by available
free space.) But on snapshot the compactor makes as may
passes as are necessary to slide all movable objects down as
far as possible. Unfortunately there is a bug in this second
pass.</div>
<div><br>
</div>
<div>Fixing this bug is now my priority. I have an example
image from Esteban Lorenzano to test. I am asking anyone else
that can provide an image that reliably crashes when trying to
save it to make the image and changes available to me for
testing if possible.</div>
<div><br>
</div>
<div>In the mean time one may be able to work around the problem
by doing a full garbage collect before snapshot. This should
do a GC with a single compaction pass which should not fail,
and then make it much more likely that the GC during snapshot
will do a single compaction pass, since fewer objects should
be mobile after the single pass compaction in the explicit GC.</div>
<div><br>
</div>
<div>To do this in Pharo I would put a full gc here:</div>
<div><br>
</div>
<div>
<div>SessionManager>>snapshot: save andQuit: quit</div>
<div><span class="gmail-Apple-tab-span" style="white-space:
pre;"> </span>| isImageStarting snapshotResult |</div>
<div><span class="gmail-Apple-tab-span" style="white-space:
pre;"> </span>ChangesLog default logSnapshot: save
andQuit: quit.</div>
<div><span class="gmail-Apple-tab-span" style="white-space:
pre;"><br>
</span></div>
<div><span class="gmail-Apple-tab-span" style="white-space:
pre;">>> SmalltalkImage current
primitiveGarbageCollect.</span></div>
<div><span class="gmail-Apple-tab-span" style="white-space:
pre;"><br>
</span></div>
<div><span class="gmail-Apple-tab-span" style="white-space:
pre;"> </span>self currentSession stop: quit.<span
class="gmail-Apple-tab-span" style="white-space: pre;"> </span>"Image
not usable from here until the session is restarted!"</div>
</div>
<div>...</div>
<div><br>
</div>
<div>In Squeak I would put a full GC here:</div>
<div><br>
</div>
<div>
<div>snapshot: save andQuit: quit withExitCode: exitCode
embedded: embeddedFlag</div>
<div><span class="gmail-Apple-tab-span" style="white-space:
pre;"> </span>"Mark the changes file and close all files
as part of #processShutdownList.</div>
<div><span class="gmail-Apple-tab-span" style="white-space:
pre;"> </span>If save is true, save the current state of
this Smalltalk in the image file.</div>
<div><span class="gmail-Apple-tab-span" style="white-space:
pre;"> </span>If quit is true, then exit to the outer OS
shell.</div>
<div><span class="gmail-Apple-tab-span" style="white-space:
pre;"> </span>If exitCode is not nil, then use it as exit
code.</div>
<div><span class="gmail-Apple-tab-span" style="white-space:
pre;"> </span>The latter part of this method runs when
resuming a previously saved image. This resume logic checks
for a document file to process when starting up."</div>
<div><br>
</div>
<div><span class="gmail-Apple-tab-span" style="white-space:
pre;"> </span>| resuming msg |</div>
<div><span class="gmail-Apple-tab-span" style="white-space:
pre;"> </span>Object flushDependents.</div>
<div><span class="gmail-Apple-tab-span" style="white-space:
pre;"> </span>Object flushEvents.</div>
<div><br>
</div>
<div><span style="white-space: pre;">...</span></div>
<div><span class="gmail-Apple-tab-span" style="white-space:
pre;"> </span>Smalltalk processShutDownList: quit.</div>
<div>>><span style="white-space: pre;"> SmalltalkImage
current primitiveGarbageCollect.</span></div>
<div><span class="gmail-Apple-tab-span" style="white-space:
pre;"> </span>Cursor write show.</div>
<div><span class="gmail-Apple-tab-span" style="white-space:
pre;"> </span>save ifTrue: [resuming := embeddedFlag </div>
<div><span class="gmail-Apple-tab-span" style="white-space:
pre;"> </span>ifTrue: [self snapshotEmbeddedPrimitive] </div>
<div><span class="gmail-Apple-tab-span" style="white-space:
pre;"> </span>ifFalse: [self snapshotPrimitive]] "<--
PC frozen here on image file"</div>
<div><span class="gmail-Apple-tab-span" style="white-space:
pre;"> </span>ifFalse: [resuming := false].</div>
</div>
<div><br>
</div>
<div>I do apologise for the bug. I hope it will be fixed within
a few days.</div>
<div><br>
</div>
<div class="gmail_signature">
<div dir="ltr">
<div><span style="font-size: small; border-collapse:
separate;">
<div>_,,,^..^,,,_<br>
</div>
<div>best, Eliot</div>
</span></div>
</div>
</div>
</div>
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_______________________________________________
Cuis-dev mailing list
<a class="moz-txt-link-abbreviated" \
href="mailto:Cuis-dev@cuis-smalltalk.org">Cuis-dev@cuis-smalltalk.org</a> <a \
class="moz-txt-link-freetext" \
href="http://cuis-smalltalk.org/mailman/listinfo/cuis-dev_cuis-smalltalk.org">http://cuis-smalltalk.org/mailman/listinfo/cuis-dev_cuis-smalltalk.org</a>
</pre>
</blockquote>
<br>
<br>
<pre class="moz-signature" cols="72">--
Juan Vuletich
<a class="moz-txt-link-abbreviated" \
href="http://www.cuis-smalltalk.org">www.cuis-smalltalk.org</a> <a \
class="moz-txt-link-freetext" \
href="https://github.com/Cuis-Smalltalk/Cuis-Smalltalk-Dev">https://github.com/Cuis-Smalltalk/Cuis-Smalltalk-Dev</a>
@JuanVuletich</pre>
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