Download as PDF, PPTX
Advanced debugging
- 1.
- 2. LLDB • Debugger inXcode • LLDB replaced GDB • Xcode 5 • Clang is an "LLVM native" C/C++/Objective-C compiler
- 3.
- 4.
- 5.
- 6.
- 7.
- 8. Dynamic Dispatch • Usefinal keyword • Declaration can’t be overridden • Allows the compiler to safely elide dynamic dispatc indirection. • final keyword enables the sealing of classes and methods.
- 9. Dynamic Type inLLDB
- 10. Dynamic Type inLLDB
- 11.
- 12.
- 13.
- 14.
- 15. Objective C andSwift Variable View
- 16. Objective C andSwift Expression
- 17. Objective C andSwift Expression
- 18. Objective C andSwift Expression Can’t access utcDate Expression modify variable of program
- 19. Data Formatters forSwift Objects
- 20. Data Formatters forSwift Objects
- 21.
- 22.
- 23.
- 24.
- 25. Commands lldb • bugreport(full report of current app’s state) • frame info • refcount (shows you reference count for the specific object)
- 26.
- 27. Control app’s execution flow •Automate debugging. Stuffs • Speedup Debugging Process
- 28.
- 29.
- 30.
- 31.
- 32.
- 33.
- 34.
- 35.
- 36.
- 37. View Hierarchy Debugging •Ability to inspect UI hierarchy • app’s hierarchy, views, constraints, and view controllers, displayed as a hierarchical list • Object inspector and size inspector
- 38.
- 39.
- 40.
- 41. Address Sanitizer • Trackdown memory violations • Finds memory corruptions • Finds Memory errors at runtime • LLVM based tool for C languages and Swift • These crashes are not deterministic
- 42. Limitation • Detect memoryerrors at runtime • Cannot detect memory leaks • Cannot detect access uninitialised memory
- 43.
- 44. Address Sanitizer • strlen(s) givesyou the length of the string held in the s variable, up to the first NULL character
- 45.
- 46.
- 47.
- 48. Out-of-Scope Solution 1)Variable aren’t accessedoutside of their scope 2)Allocate memory using malloc function
- 49. Use of StackMemory After Function Return
- 50. Use of StackMemory After Function Return • Function returns a pointer to its local variable • Once the function returns, that pointer is no longer valid • If we use we are again accessing garbage memory • Either crash or unexpected behaviour
- 51. Solution • Use pointerarguments
- 52. Memory Graph Debugger • Find retain cycle • Find memory leaks • Pause app execution when activated • Display objects currently in a heap • Live Allocations uncheck when not using • Clean build when using
- 53. 1) How toUse
- 54. 2) How toUse
- 55.
- 56.
- 57.
- 58. Memory Leaks Controller TableView VisibleCell Visible Cell Visible Cell Visible Cell Closure
- 59.
- 60. Thinking • Pop Controller •Why it still in heap • dealloc also not called • Not a simple leak so Memory Graph Debugger don’t tell • Using heap content we identify
- 61.
- 62.
- 63. Memory Leaks No controllerin heap content also
- 64. Thread Sanitizer (TSan) ThreadingIssues • Hard to consistently reproduce • Difficult to debug (Timing matter) • Lead to unpredictable results
- 65. Thread Sanitizer (TSan) •Use of uninitialised mutexes • Thread leak (missing pthread_join) • Unsafe calls in signal handlers • Unlock from wrong thread • Data races / Race condition (access same memory location without proper sync ) • Xcode 8
- 66.
- 67.
- 68.
- 69.
- 70.
- 71.
- 72. Lazy Initialization inObjective C
- 73.
- 74.
- 75.
- 76. Swift Access Races •Multiple threads call a mutating method on Structs • Pass a shared variable as inout without systematic manner • Access races can result in unpredictable behavior
- 77.
- 78. Races on Collectionsand Other APIs
- 79. Races on Collectionsand Other APIs
- 80. Uninitialised Mutexes • Detectswhen a mutex is used before it’s initialized. • pthread_mutex_lock(_:) or pthread_mutex_unlock(_:) is called with a pthread_mutex_t variable that wasn’t initialized • Attempting to use an uninitialized mutex results in an error
- 81.
- 82.
- 83. Main Thread Checker •Detect invalid use of AppKit, UIKit, and other APIs from a background thread. • Missed UI updates • Visual defects
- 84.
- 85.
- 86. Static Analyzer • Findbugs in your code before you even run your app • Possible code paths in a few seconds, reporting potential bugs • Identifies areas in your code that don’t follow recommended API
- 87.
- 88. Problems • Logic flaws,such as accessing uninitialized variables and dereferencing null pointers • Dead store (unused variable) flaws • API usage flaws
- 89.