It’s been said that the first 90% of a project consumes 90% of the time, whereas the second 10 % accounts for the other 90% of the time. One reason might be because elevating software from “mostly works” to robust and supportable requires an attention to detail in the parts of a system that are usually mocked out during unit testing. It’s all too easy to focus on testing the happy paths and gloss over the more tricky design problems such as how to handle a full disk or Cheshire cat style network. This session delves into those less glamorous non-functional requirements that crop up the moment you start talking to hard disks, networks, databases, etc. Unsurprisingly it will have a fair bit to say about detecting and recovering from errors; starting with ensuring that you generate them correctly in the first place. This will undoubtedly lead on to the aforementioned subject of testing systemic effects. Finally there will also be diversions into the realms of monitoring and configuration as we look into the operational side of the code once it’s running. At the end you will hopefully have smiled at the misfortune of others (mostly me) and added a few more items to the ever growing list of “stuff I might have to think about when developing software”.

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