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Addressing Unbounded Heap Growth in C++: Detection Strategies

Learn about diagnosing unbounded heap growth in C++ with detection approaches such as CAT, growth tracking, and automated tests. Discover how to identify memory tumors and prevent memory leaks effectively.

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Addressing Unbounded Heap Growth in C++: Detection Strategies

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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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