[fdo-internals] gcc mt_alloc related bugs?

[Traian Stanev]

Yikes! I think a repressed memory is coming back. I gave up on getting my x64 MapGuide build to run after failing to resolve such an error in Xalan strings. I was using gcc 3.4 also.
 
Traian
 

	-----Original Message----- 
	From: fdo-internals-bounces at lists.osgeo.org on behalf of Frank Warmerdam (External) 
	Sent: Fri 2/16/2007 3:26 AM 
	To: FDO Internals Mail List 
	Cc: 
	Subject: [fdo-internals] gcc mt_alloc related bugs? 
	
	

	Folks,
	
	I mentioned a couple days ago that I was still seeing crashes under
	some circumstances after my 64bit fixes.  I have spent more hours than
	I wish to contemplate digging into these crashes and have not come up
	with a particular satisfying answer.
	
	The crashes seemed to be related to corruption of the freelist
	datastructures maintained by the mt_alloc allocator for stl vector
	objects (ie. the XalanDOMString).
	
	On Linux with glibc it seems you can define the environment variable
	GLIBCXX_FORCE_NEW to force a new and delete to be done each time stl
	container allocate or free memory, instead of using the mt_alloc pool
	allocator.  This seems to avoid the problem.  I *thought* when running
	in this mode I would finally be able to find the bug in the FDO code
	using valgrind, but things run perfectly clean!
	
	Based on a variety of googling, I am now suspecting that my Ubuntu
	gcc 3.4 build is suffering from the problem described at:
	
	   http://bugs.donarmstrong.com/cgi-bin/bugreport.cgi?bug=293466
	
	So, if people are running into strange crashes, and tracebacks in
	gcc show it being deep in the glibc mt_allocator while destroying
	XalanDOMString's, I would suggest defining the GLIBCXX_FORCE_NEW
	environment variable.  I results in a 20-30% speed reduction in
	the FDO core unit tests, so there is a performance impact.  But things
	run clean.
	
	I *imagine* this is fixed in newer versions of Debian/Ubuntu.  I'm running
	one generation behind (Ubuntu Breezy Badger).
	
	God my head hurts.
	
	PS. Google on mt_alloc and GLIBCXX_FORCE_NEW is educational for those
	so inclined.  Mateusz - please read up on this so you can help me next time
	I have this problem, and I've completely forgotten what I learned this time.
	
	:-)
	
	Now enjoying my FDO Core UnitTest results:
	
	OK (102)
	
	
	Best regards,
	--
	---------------------------------------+--------------------------------------
	I set the clouds in motion - turn up   | Frank Warmerdam, warmerdam at pobox.com
	light and sound - activate the windows | http://pobox.com/~warmerdam
	and watch the world go round - Rush    | President OSGeo, http://osgeo.org
	
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