1. Error Handling

2. COSC 494: Human-Centric Software Engineering
State of the practice in SE tools
Demo tools in class
State of the art in SE research
Discuss research papers
Adv topics in SE
Code reviewing, continuous integration
Program analysis, empirical methods
Design, implement, and evaluate an SE tool
Individual project

3. var contents = File.ReadAllText(”settings.txt");
What if file isn’t there? CRASH!

4. if(File. Exists(“settings. txt”)) { var contents = File
if(File.Exists(“settings.txt”)) { var contents = File.ReadAllText(”settings.txt"); }
What if file isn’t there? CRASH!

6. Does your program handle everything?
File doesn’t exist
File contents are not as expected
Connection to database fails
Users enter invalid input

7. Check for errors What assumptions are you making?
Could a value be null?
Are there error codes?
Special cases?
String.IndexOf()
Returns -1 if doesn’t exist
StringReader.ReadLine()
Returns null if there are no more
Enumerable.Filter()
Returns [] if doesn’t exist
String.Contains()
Returns false if doesn’t exist
String.Substring()
Returns “” if doesn’t exist

8. How to handle errors? End the program Ostrich algorithm
Notify the user with clear explanation
Return the program to a valid state
Retry
Catch the exception

9. Retry Logic
data = httpClient.Get(“ attempts = 0; do { attempts++; data.status = httpClient.Get(“ if(data == SUCCESS) { break; } sleep(delay); } while (tries < maxAttempts); HandleFailure();

10. Exception Handling
try { // Code that might fail } catch { // Code to handle the failure finally { // Optional: clean up after the try and catch

11. Downsides of error handling
Lots of added code
Makes code complex and hard to read
Hard to test
Exceptions are fancy GOTOs
Advice?
Reduce the number of potential errors
Recover when possible
Provide helpful error messages
Keep code clean
Don’t be lazy

12. A bad error message

13. A bad error message

14. A good error message

15. Gracefully handle crashes
when possible
Provide helpful message to user
Log the crash along with info to debug
The error/exception
Where it occurred
Any info to help replicate
Clean up
Don’t leave files in corrupt state
Close connections and deallocate memory