The document discusses robust software development practices, focusing on error handling, exception safety, and unit testing failures. It emphasizes the importance of managing unexpected behavior through appropriate exit codes, try-catch blocks, and exception-safe code. Additionally, it touches on flexible configurations, monitoring clarity, and strategies for handling cancellable operations.

1. Robust Software –Robust Software –
Dotting the I’s andDotting the I’s and
Crossing the T’sCrossing the T’s
Chris OldwoodChris Oldwood
ACCU Conference 2013ACCU Conference 2013
@chrisoldwood / gort@cix.co.uk@chrisoldwood / gort@cix.co.uk

2. The I’s & T’sThe I’s & T’s
 RobustnessRobustness
 Handling ErrorsHandling Errors
 Safely Ignoring ErrorsSafely Ignoring Errors
 TimeoutsTimeouts
 Unit Testing FailuresUnit Testing Failures
 Flexible ConfigurationFlexible Configuration
 Monitoring ClarityMonitoring Clarity

3. RobustnessRobustness

4. Stable in the face ofStable in the face of
unexpected behaviourunexpected behaviour

5. Pop Quiz – Exit Code?Pop Quiz – Exit Code?
int main(int argc, char* argv[])
{
throw UnhandledException();
}

6. Exit Code ConventionExit Code Convention
program.exe
if %errorlevel% neq 0 (
echo ERROR: Program failed
exit /b 1
)

7. Big Outer Try BlockBig Outer Try Block
int main(int argc, char* argv[])
{
try
{
return DoUsefulWork(argc, argv);
}
catch (const std::exception& e)
{ /* Report failure */ }
catch (…)
{ /* Report failure */ }
return EXIT_FAILURE;
}

8. Module BoundariesModule Boundaries
HRESULT DoSomething(...)
{
try
{
return Impl::DoSomething(...);
}
catch (const std::bad_alloc& e)
{ return E_OUTOFMEMORY; }
catch (const std::exception& e)
{ return E_FAIL; }
catch (...)
{ return E_UNEXPECTED; }
}

9. Exception Safety GuaranteesException Safety Guarantees
 NoneNone
 BasicBasic
 StrongStrong
 No ThrowNo Throw

10. Exception Unsafe CodeException Unsafe Code
IServicePtr AcquireService()
{
if (!m_service)
{
m_service = new Service();
m_service.CreateInstance();
}
return m_service;
}
IServicePtr m_service;

11. Exception Safe CodeException Safe Code
IServicePtr AcquireService()
{
if (!m_service)
{
ServicePtr service = new Service();
service.CreateInstance();
m_service.swap(service);
}
return m_service;
}
IServicePtr m_service;

12. Forever is a Really Long TimeForever is a Really Long Time
Handle completed = BeginAsyncOperation();
. . .
Wait(completed, INFINITE);

13. Cancellable OperationsCancellable Operations
Handle completed = BeginAsyncOperation();
Handle aborted = GetAbortHandle();
Handle waitables[] = { aborted, completed };
. . .
Handle signalled = Wait(waitables, timeout);
if (signalled == aborted)
{

14. Retries: immediate then queuedRetries: immediate then queued

15. Unit Testing FailuresUnit Testing Failures

16. Testing Write+Rename IdiomTesting Write+Rename Idiom
[Test]
public Void OriginalFilePreservedOnException()
{
var fakeIo = new FakeIo();
fakeIo.Write = (file, buffer) =>
{ throw new IoException(); }
var writer = new WriterService(fakeIo);
var filename = “original.txt”;
Assert.Throws(() => writer.WriteFile(filename));
Assert.True(fakeIo.FileExists(filename));
Assert.That(. . .);
}

17. Flexible ConfigurationFlexible Configuration

18. Monitoring ClarityMonitoring Clarity

19. Release It!Release It!

20. Questions?Questions?

21. Blog:Blog:
http://chrisoldwood.blogspot.comhttp://chrisoldwood.blogspot.com
@chrisoldwood / gort@cix.co.uk@chrisoldwood / gort@cix.co.uk