[asterisk-bugs] [Asterisk 0017277]: [patch] The heap data structure can't cope with a removal and reinsert

Thu May 6 09:04:39 CDT 2010

A NOTE has been added to this issue. 
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https://issues.asterisk.org/view.php?id=17277 
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Reported By:                cappucinoking
Assigned To:                russell
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Project:                    Asterisk
Issue ID:                   17277
Category:                   Tests/General
Reproducibility:            always
Severity:                   block
Priority:                   normal
Status:                     closed
Asterisk Version:           SVN 
JIRA:                       SWP-1405 
Regression:                 No 
Reviewboard Link:            
SVN Branch (only for SVN checkouts, not tarball releases): 1.6.2 
SVN Revision (number only!):  
Request Review:              
Resolution:                 fixed
Fixed in Version:           
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Date Submitted:             2010-05-03 12:42 CDT
Last Modified:              2010-05-06 09:04 CDT
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Summary:                    [patch] The heap data structure can't cope with a
removal and reinsert
Description: 
Whilst looking into why qualify events are being scheduled out of sequence
I started looking into why items on the maxheap weren't in the correct
order.
The qualify code is a different use case then the current tests allow for.
When a response to a qualify request is made, the event is rescheduled via
a remove and re-add to the maxheap structure.
I have written a test to demonstrate the failure of the heap to keep the
items in order when removing and re-inserting items.

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Relationships       ID      Summary
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related to          0016936 [patch] Qualify frequency has big pause...
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 (0121471) svnbot (reporter) - 2010-05-06 09:04
 https://issues.asterisk.org/view.php?id=17277#c121471 
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Repository: asterisk
Revision: 261498

_U  branches/1.6.2/
U   branches/1.6.2/main/heap.c

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r261498 | russell | 2010-05-06 09:04:36 -0500 (Thu, 06 May 2010) | 47
lines

Merged revisions 261496 via svnmerge from 
https://origsvn.digium.com/svn/asterisk/trunk

........
  r261496 | russell | 2010-05-06 08:58:07 -0500 (Thu, 06 May 2010) | 40
lines

  Fix handling of removing nodes from the middle of a heap.

  This bug surfaced in 1.6.2 and does not affect code in any other
released
  version of Asterisk.  It manifested itself as SIP qualify not happening
when
  it should, causing peers to go unreachable.  This was debugged down to
scheduler
  entries sometimes not getting executed when they were supposed to, which
was in
  turn caused by an error in the heap code.

  The problem only sometimes occurs, and it is due to the logic for
removing an entry
  in the heap from an arbitrary location (not just popping off the top). 
The scheduler
  performs this operation frequently when entries are removed before they
run (when
  ast_sched_del() is used).

  In a normal pop off of the top of the heap, a node is taken off the
bottom,
  placed at the top, and then bubbled down until the max heap property is
restored
  (see max_heapify()).  This same logic was used for removing an arbitrary
node
  from the middle of the heap.  Unfortunately, that logic is full of fail.
 This
  patch fixes that by fully restoring the max heap property when a node is
thrown
  into the middle of the heap.  Instead of just pushing it down as
appropriate, it
  first pushes it up as high as it will go, and _then_ pushes it down.

  Lastly, fix a minor problem in ast_heap_verify(), which is only used for
  debugging.  If a parent and child node have the same value, that is not
an
  error.  The only error is if a parent's value is less than its children.

  A huge thanks goes out to cappucinoking for debugging this down to the
scheduler,
  and then producing an ast_heap test case that demonstrated the breakage.
 That
  made it very easy for me to focus on the heap logic and produce a fix. 
Open source
  projects are awesome.

  (closes issue https://issues.asterisk.org/view.php?id=16936)
  Reported by: ib2
  Tested by: cappucinoking, crjw

  (closes issue https://issues.asterisk.org/view.php?id=17277)
  Reported by: cappucinoking
  Patches:
        heap-fix.rev2.diff uploaded by russell (license 2)
  Tested by: cappucinoking, russell
........

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http://svn.digium.com/view/asterisk?view=rev&revision=261498 

Issue History 
Date Modified    Username       Field                    Change               
====================================================================== 
2010-05-06 09:04 svnbot         Checkin                                      
2010-05-06 09:04 svnbot         Note Added: 0121471                          
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