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Diagnosing Unbounded Heap Growth in C++ Problem Description

Diagnosing Unbounded Heap Growth in C++ Problem Description. Types of Unbounded Heap Growth Reference Lost (Leak) Reference lost to memory without freeing it Well studied, wide variety of tools that identify leaks Reference Retained But no longer needed

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Diagnosing Unbounded Heap Growth in C++ Problem Description

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  1. Diagnosing Unbounded Heap Growth in C++Problem Description • Types of Unbounded Heap Growth • Reference Lost (Leak) • Reference lost to memory without freeing it • Well studied, wide variety of tools that identify leaks • Reference Retained • But no longer needed • On shutdown, memory freed, so not reported as leak • If growing, it’s accumulating in a data structure • Few tools exist to deal with this problem in C++ • Valgrind, IBM Rational Purify, Insure++ do not detect this • Generally also referred to as a leak

  2. Diagnosing Unbounded Heap Growth in C++Problem Description • Memory Tumor • Data structure with unbounded growth • Examples: • Storing unlimited history info in memory • Incorrect removal functions • Simplest example: void main() { std::vector<int> tumorV; while( inputKey != ESC ) tumorV.push_back(1); }

  3. Diagnosing Unbounded Heap Growth in C++Detection Approach • 3 Aspects of Tumor Detection • Container tracking • Hold references to all data structures in the system • Growth tracking • Track size changes per data structure over time • Report those with unbounded growth • Automated Test • Created by user to exercise all code paths

  4. Diagnosing Unbounded Heap Growth in C++ Review • Container tracking • CAT (Central Aggregate Tracker) • Maintains references to all aggregates in the system • Create wrappers for each aggregate type in system • Templated constructors, multiple inheritance • Add to CAT on construction, remove on destruction • Namespace replacement to enable wrappers • Find and replace to apply new namespace • Wrappers disabled with compile time flag • Example: trak::std::vector<int>

  5. Diagnosing Unbounded Heap Growth in C++ Detection Approach • Growth Tracking • Take periodic samples of the CAT • Exponentially increasing interval sizes • Reduces false positives & negatives over time • Report growing aggregates at each sample

  6. Diagnosing Unbounded Heap Growth in C++Testing • Automated Test • Detecting growth requires a test that exhibits the growth • Good complete test design is important • Need cyclic tests that cover all code paths • May require multiple tests • Slow growing tumors may grow quickly with different usage patterns • Eg. WebKitMiniBrowser pop-up windows

  7. Diagnosing Unbounded Heap Growth in C++ Detection Approach • Growth Tracking • Heuristic • Take periodic samples of the CAT • Two Interval Analysis • 1st interval establishes aggregate age, gives time to stabilize • 2nd interval proves stability, non-tumors shouldn’t grow • 2nd interval becomes the 1st for next more accurate test

  8. Diagnosing Unbounded Heap Growth in C++ Detection Approach • Growth Tracking • Two interval analysis 4 2 3 1 memory time

  9. Diagnosing Unbounded Heap Growth in C++ Detection Approach • Growth Tracking • Two interval analysis Reported as tumor (false positive) Not reported (growth stabilized) 4 2 3 1 memory time

  10. Diagnosing Unbounded Heap Growth in C++ Detection Approach • Growth Tracking • Heuristic • Take periodic samples of the CAT • Two Interval Analysis • 1st interval establishes aggregate age, gives time to stabilize • 2nd interval proves stability, non-tumors shouldn’t grow • 2nd interval becomes the 1st for next more accurate test • Exponentially increasing interval sizes • Reduces false positives & negatives over time

  11. Diagnosing Unbounded Heap Growth in C++ Detection Approach • Growth Tracking • Exponentially increasing interval size In this example: constant intervals would not report growth half the time 4 2 3 1 memory time

  12. Diagnosing Unbounded Heap Growth in C++ Detection Approach • Growth Tracking • Heuristic • Take periodic samples of the CAT • Two Interval Analysis • 1st interval establishes aggregate age, gives time to stabilize • 2nd interval proves stability, non-tumors shouldn’t grow • 2nd interval becomes first for next more accurate test • Exponentially increasing interval sizes • Reduces false positives & negatives over time • Monitor size maximums • Reduces size fluctuation false positives

  13. Diagnosing Unbounded Heap Growth in C++ Detection Approach • Growth Tracking • Max size variable Growth would be reported without max size 4 2 3 1 ceiling memory time

  14. Diagnosing Unbounded Heap Growth in C++ Detection Approach • Growth Tracking • Heuristic • Take periodic samples of the CAT • Two Interval Analysis • 1st interval establishes aggregate age, gives time to stabilize • 2nd interval proves stability, non-tumors shouldn’t grow • 2nd interval becomes the 1st for next more accurate test • Exponentially increasing interval sizes • Reduces false positives & negatives over time • Monitor size maximums • Reduces size fluctuation false positives • At each interval report all aggregates that: • Increased their size maximum • Have existed for two full intervals • Sort results by size & reporting frequency to prioritize investigation

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