Debugging
Telerik Academy Alpha

 

HQC

 Table of contents

  • Introduction to Debugging

  • Visual Studio Debugger

  • Breakpoints

  • Data Inspection

  • Threads and Stacks 

Introduction to Debugging

Why debugging?

 Debugging
 

The process of locating and fixing or bypassing bugs (errors) in computer program code

  Steps

  1. Problem + stable source state
     
  2. Isolation of the problem
     
  3. Write tests
     
  4. Fix the problem and commit/ check-in it in the source control

 

 

Note: One change at a time

 Testing vs Debugging

Initial detection of errors

Diagnosing and correcting the root causes of errors that have already been detected

 Importance of Debugging

  • Perfect code is an illusion
  • Debugging can viewed as one big decision tree
    • Individual nodes represent theories
    • Leaf nodes represent possible root causes
  • You should be able to debug code that is written years ago
  • $60 Billion per year in economic losses due to software defects (in USA only)

 How to avoid bugs

  • Reduce the number of code lines
    • Write less and write smarter. Keep it simple.
  • Reduce complexity / Good code separation
    • Reduce the number of possible code paths
  • Unit test (TDD) with almost 100% test coverage
  • Always assume your code is not working
    • Prove it otherwise!
    • Always check the code you write
  • Experience matters / Read, learn, code

Visual Studio Debugging

 Visual Studio Debugger

  • Breakpoints
     
  • Visualize the program flow
     
  • Control the flow of execution
     
  • Data tips
     
  • Watch variables
     
  • Debugging multi-threaded programs

 Debug Windows

Menu

Windows

 Debug Toolbar

Step into (F11)

Step over (F10)

Step out (Shift + F10)

Stop debugging

Continue (F5)

 Controlling Execution

  • By default, an app will run uninterrupted (and stop on exception or breakpoint)
     
  • Debugging is all about looking at the state of the process
     
  • Controlling execution allows:
    • Pausing and resuming execution
    • Stepping through the application in smaller chunks
    • In the case of IntelliTrace (recording steps) - backward and forward stepping

IntelliTrace

Record and trace your code's execution history

 IntelliTrace

  • IntelliTrace operates in the background, records what you are doing during debugging
     
  • You can easily get a past state of your application from the IntelliTrace
     
  • You can navigate your code to any part and see what has happened
    • To navigate, just click any of the events that you want to explore

 Options and Settings

Ignore other code

Debug .Net source

Load symbols (pdb) of a dll

Breakpoints

 Breakpoints

Ability to stop execution based on certain criteria is key when debugging

When data changes

When a function is hit

When a specific thread hits a function

A hit count

Condition

Filters

 Visual Studio Breakpoints

Breakpoint settings:

  • Debug->Toggle breakpoint
  • F9 shortcut
  • Clicking on the leftmost side of the source code window

 Managing Breakpoints

  • Features:
     

    • Add breakpoints

    • Remove or disable breakpoint

    • Label or group breakpoints

    • Export/import breakpoints

Data Inspection

 Data Inspection

  • Debugging is all about data inspection
    • What are the local variables?
    • What is in memory?
    • What is the code flow?
    • In general - What is the state of the process right now and how did it get there?
  • As such, the ease of data inspection is key to quick resolution of problems

 Data Inspection

  • Visual Studio offers great data inspection features
    • Watch windows
    • Autos and Locals
    • Memory and Registers
    • Data Tips
    • Immediate window

 Watch window

  • Allows you to inspect various states of your application
  • Several different kinds of “predefined” watch windows
    • Autos
    • Locals
       
  • “Custom” watch windows 
    • Contain only variables that you choose to add
    • Right click on the variable and select “Add to Watch”

 Autos and Locals

  • Locals watch window contains the local variables for the specific stack frame
    • Debug -> Windows -> Locals
    • Displays: name of the variable, value and type
    • Allows drill down into objects by clicking on the + sign in the tree control
  • Autos lets the debugger decide which variables to show in the window
    • Loosely based on the current and previous statement

 Data Tips

  • Provides information about variables
    • Variables must be within scope of current execution
  • Place mouse pointer over any variable
    • Variables can be expanded by using the + sign
  • Pinning the data tip causes it to always stay open
  • Comments can be added to data tips
  • Data tips support drag and drop
  • Importing and exporting data tips

 Immediate Window

  • Useful when debugging due to the expansive expressions that can be executed
    • To output the value of a variable
    • To set values, use =
    • To call a method, use .(arguments)
    • Similar to regular code
    • Supports Intellisense

Threads and Stacks

 Threads

  • Fundamental unit of code execution
  • Commonly, more than one thread
    • .NET, always more than one thread
  • Each thread has a memory area associated with it known as a stack used to
    • Store local variables
    • Store frame specific information
  • Memory area employs last-in-first-out semantics

 Threads Window

  • Contains an overview of thread activity in the process
  • Includes basic information in a per thread basis
    • Thread ID’s
    • Category
    • Name
    • Location
    • Priority

 Callstacks

  • A threads stack is commonly referred to as a callstack
  • Visual Studio shows the elements of a callstack
    • Local variables
    • Method frames

Questions

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