Monthly Archives: June 2011

Jun 07 2011
story

FTP – A connection to my nightmere

Story time again I guess.

Although this is not a pleasant tale, even remembering some of the details make me squirm in discomfort still.

I remembered it was a Tuesday night, 10 pm, I was wrapping up my photo editing work and getting ready for bed, when a call came to me. It was the support guy from work, he calls to inform me that the prices for some ETFs have not came through. Since there was a new production deployment of the ETL software responsible for sending the prices through the day before, he assumed that the ETL software must be to blame.

Unfortunately the particular colleague that deployed the changes yesterday had turned off her phone, “clever girl” I whispered to myself. Since I was the next person with knowledge on the software, it was up to me to debug the situation.

The first thing I did was to bring up a diff of the code been deployed, I traced through all the configuration changes, everything seem innocent enough. Certainly nothing that will stop the file been picked up from source ftp location to the destination.

Just to be safe, I reversed the changes, most of which are superficial, and redeployed the ETL software, since I had no production access, I IM the support guy to drop the file and try again. The support guy regret to inform me that, the file was again not picked up, completed ignored by the software.

By that point it was close to midnight, and my memory became hazy, but the loop went on something like this, I try something fix the issue, deployed it, support guy tell me it didn’t work. And on and on it went, at one point, even the programming cat that lived next door came over to help debug, he too was stumped. This cycle continued to 3 am.

I was tired and broken by then, my mind was a mess of tangled wires and burnt fuses. But at last, something came to me, something ridiculous in its simplicity.

I asked the support guy, “hey, which FTP are you putting the file in?”

“FTP a of course”

My rage burned with the heat of a thousand suns.

“NO! NO! NO! NEIN! NEIN! NEIN! NEIN! FTP a is the destination FTP, you have to put the file in FTP b, this is an outgoing file not an incoming file!” I might have been more polite had this not been common knowledge and detailed in the support document they made us write.

So another 30 minutes was wasted restoring all the changes back, and redeploy the latest version, and waiting for the support guy to put the file on the correct FTP server, and of course, everything flowed after that.

Lesson to take away from this? If nothing makes sense, question your/their assumptions.

Tagged
Jun 07 2011
story

House MD debugging

I did a quick search around the interweb. There is no precedence, so i would like to officially coin the pharse House MD debugging.

Official definition: a way to discover the source of the bug by eliminting the impossible and whatever remains, although unlikely, must be the cause. It is also known as the Sherlock Holmes deduction method.

Most of the bugs I have encounted are obvious, with nice stacktrace to help track it down to the line number. Some bugs however, through complexity of configuration or external library obsfucation, hides the source of the bug in a maze of incoherent logics. That’s the perfect time to use HMD!

Just like how House determine the real disease on the show, we can get to root of the cause of the bug by testing all sub component that could possibly cause the problem. Once we discover the offending component, sub divide the areas to test for once more and continue until the bug is found.

So give it a try next time you find a mystey bug, and watch House MD, it’s a great show.

Tagged
Jun 07 2011
story

Log debug and Hibernate, a tale of two environments

Cute story.

A couple of years back I got a call for support with a recently released webapp. User is complaining that a particular functionality was returning the following hibernate exception.

org.hibernate.LazyInitializationException: could not initialize proxy – the owning Session was closed

A quick source check have indeed shown that the field in question was lazy initialised when it should not have been. But the puzzle remains, it worked in UAT environment. In fact it was extensively tested by the particular user who reported the issue before it was released into production. Not to mention all the developer testing that was done.

The simple explanation would be, we simply missed that particular functionality when we did the test. But that was soon ruled out as in UAT, the bug was still not rearing it’s ugly stack trace. So, what was it in production that is making it fail?

As it turned out, the correct question should be, what was in UAT that made it work? This:

if (logger.isDebugEnabled()) {    
  logger.debug(dataMap.toString());
}

The reason it was working UAT was because log was set to debug in that environment, while in production it was set to info only. Having the dataMap.toString() called in that debug block means hibernate actually went and fetched the lazy initialised data, as oppose to in production where the first time the code needed dataMap, the hibernate session was already closed.

I’m still not sure what exact lesson I should take away from this, but it sure was an interesting code mystery.

Tagged ,
Jun 07 2011
story

Android “Fling” Gesture Detection

Had some issues last night trying to get my Android game to detect the fling gesture, basically a click and drag in mouse world.

I had the following code in my little View object.

private GestureDetector gestureDetector;
private View.OnTouchListener gestureListener;// Gesture detection
    gestureDetector = new GestureDetector(new MyGestureDetector());
    gestureListener = new View.OnTouchListener() {
        public boolean onTouch(View v, MotionEvent event) {
            if (gestureDetector.onTouchEvent(event)) {
                return true;
            }
            return false;
        }
    };
this.setOnTouchListener(gestureListener);

  * Handle any fling action here
  * @author dracox
  *
  */
 protected class MyGestureDetector extends SimpleOnGestureListener {
  /**
   * We need to capture any user line drawn request here.
   */
  @Override
  public boolean onFling(MotionEvent e1, MotionEvent e2, float velocityX, float velocityY) {
   //This should only be caring about flings after init
   gameWalls.add(new FireWall(new Point((int)e1.getRawX(), (int)e1.getRawY()), new Point((int)e2.getRawX(), (int)e2.getRawY())));
   return true;
  }
 }

I fired up my emulator, but was not getting any fling action logged. However the onTouch events were been fired off.

Initially I though maybe the emulator couldn’t handle fling event, but after much searching I found the root of the problem.

Apparently, the onDown event was fired off first, which was consumed before it became a “fling”, so I had to override that too on my custom Gesture Detector class.

I was a little puzzled about returning true for the onDown handler, as the API stated return true to consume the event and false to let it pass.

/**
 * Need to let onDown pass through, otherwise it will block the onFling event
 */
 @Override
 public boolean onDown(MotionEvent event) {
 return true;
 }

Now we’re flinging!

Tagged , ,