Slide 1Slide 2Slide 3Slide 4Slide 5Slide 6Slide 7Slide 8Slide 9Slide 10Slide 11Cork: Dynamic Memory Leak Detection for Garbage-Collected Languages Maria Jump & Kathryn McKinleyPresented by Yuhao ZhuCS 395TMotivationGarbage collection has to be conservativeWhich leads to maintaing references to inactive objsDifficult to find these bugsMemory leak detectionEfficiencyPrecisionEasy to parseNow we have Cork!Type Points-From GraphNode: total volumn of type tEdge: t'->t where an obj of type t is pointing to obj of type t'Constructed during whole heap collection (scanning phase)Additional type lookup (upon scanning an obj)Detecting heap growthBasic idea: differencing consecutive TPFGs, but needs to consider fluctuationsRatio Ranking Technique:Decay factor (f):Phase growth factor (g): Q > 1Ranking by accumulating g over several collections, rewarding growth and penalizing decayObjs with rank > Rthreshold are considered as candidatesMemory leak localizationData structuresSlice: a path on which the ranks of all edges are positiveThe slice contains the dynamic data structures containing candidate nodesAllocation site:Reports all allocation sites for candidatesAssociate a SiteMap of a particular type with each allocation site duing compilationSeach the maps to find allocation sites for a typeOptimizationsEfficiencyOnly look at four recent TPFGsEach type has its own type information (over four collections) recorded in its Type Information BlockScalabilityEdges are linear with respect to the nodes (quadratic in theory)Remove edges from the edge pool and adding to the edge listsEvaluation44% types are resident at a timeMore than half of the edges are pruned (rank < 0)Very very little space overheadEvaluation (cont.) 11.1% to 13.2% for scan time, 12.3% to 14.9% for collector time, resulting in 1.9% to 4.0% for total timeEvaluation (cont.)Accuracy (sensitivity) analysisThe larger the better, but at some point it stopsEvaluation (cont.)Two case studies: SPECjbb2000 and EclipseFind the candidates -> correlate to the code -> localize the bugHuman ingenuity is still required!DiscussionHow to deal with unmanaged languages where type information is not contained?How to further reduce the need for programmers'
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