C# Memory Leak Torpedoed Princeton's DARPA Chances

nil0lab writes "In a case of 20/20 hindsight, Princeton DARPA Grand Challenge team member Bryan Cattle reflects on how their code failed to forget obstacles it had passed. It was written in Microsoft's C#, which isn't supposed to let you have memory leaks. 'We kept noticing that the computer would begin to bog down after extended periods of driving. This problem was pernicious because it only showed up after 40 minutes to an hour of driving around and collecting obstacles. The computer performance would just gradually slow down until the car just simply stopped responding, usually with the gas pedal down, and would just drive off into the bush until we pulled the plug. We looked through the code on paper, literally line by line, and just couldn't for the life of us imagine what the problem was.'"

Comments

Re:I'll show you mine if you..

[El Lobo]

The problem was not the garbage collector if you read TFA. The articule is just a shameless plug, some ad spam for some very obscure profile.

This just tells us once again that our wonderful editors on /. don't even try to understand what's behind an article, but they just find some sensationalistic title (the more AntiMS, the better) and done. This results in more comments of the type... "See, M$ id teh SuCkS", or "thanks god for my Linuzzz."..., so they got more profit for their /. ads (oh, the irony often MS ads, BTW).

Yellow press..... yes, I know, /. is not supposed to have any credibility like any other parasite news sites, but anyway....

Re:Stupid Slashdot headline

[blowdart]

I think you're getting hung up on the method name. There is no standard "delete" function that marks something as unused (dispose on the other hand sort of gets there). The article itself is unclear but I would assume that they were simply deleting the collision objects from a collection of potential hazards. Whilst that would remove the object from the collection itself it is *not* a delete. As references to the object existed elsewhere the object still exists (look ma, no null pointer exceptions) no delete happens. You cannot specifically say to the GC "We're done with this, delete it", the GC sweeps on a regular basis looking for objects with no references.

Would you really want the GC deciding that just because an object is no longer part of a collection it's safe to unsubscribe it from events and delete it? I know I wouldn't.

Re:Stupid Slashdot headline

[slashdot.org]

Of course you can have a memory leak in a managed language! Any Java programmer who's decent understands that.

Decent programmers might understand that, but let's be honest, it's not like Java (and other GC languages) haven't been presented as if memory leaks were a thing of the past.

As a matter of fact, some people will probably still claim that it's technically not a memory leak, but instead an object life-span issue.

What surprises me is that outspoken proponents of managed languages use the garbage collection so often as a good thing, as if now you can be a sloppier programmer and get away with it.

In reality you have to identify/control the lifespan of objects anyway, so I personally never understood what the big deal is about freeing memory manually. Not to mention that memory leaks in say, C++ code, really aren't that hard to find. The tools have become pretty freakin decent.

And also not to mention that garbage collection might be handy for memory, but memory is only one of a plethora of resources that can be leaked. And since for many resources it isn't nearly as appropriate to 'lazy' free them, as a programmer you still have to be aware of the allocate/free paradigm. (as just one silly example, it would suck if you wouldn't be able to explicitly close a file, because you can't delete it before it's closed)

In other words, you are right. Of course you can have memory leaks in garbage collected languages. And I wish people would stop using GC as an argument why languages as Java are so much better to use than C++.

Re:Slashvertisement

[jmccay]

I think this is just poor code debugging skills. The new garbage collected languages (C# and Java) seem to be creating coders that don't know the basics of debugging. If this was C++, the bug would have shown up when an event occurred and the code called a deleted object. It would have been harder to track down. In any case, I would have added code to analyze the state of the stack and it's objects since it only occurred after the program/car had been running for a while. Also, had it not occurred to them to increase the number of obstacles beyond the "controlled" environment? You can easily write test code to to add a lot of objects into the stack without the use of the car.

Our cars used an asynchronous event-based code stack written from scratch by us. They wrote their code stack from scratch. They should have modified an existing one that was proven to work. Either way, I think this is a case of sloppy programming. I don't think it is worth mention aside from the case what the closest thing to a memory leak is that you can have. Unfortunately, that too should have come to mind from them. They ruled that out because "most of [their] code is written in garbage-collected C#". Just because a language is garbage collected, it doesn't mean you can just ignore the issues. All reference to the object must be removed for it to be deleted. This is definitely a case of sloppy programming. I would be embarrassed if my name were attached to this.

      Some old Visual Basic programmer jokes come to mind when I read this article. People use to make fun of Visual Basic programmers because it was to easy to write programs in VB. They thought it would produce sloppy code with errors, and other similar things. To some extent, it appears that same case could be made for C#, and to a lesser extent Java. In the end this is simply a case of not stress testing their event stack.

Re:I'll show you mine if you..

[WED Fan]

Slashdot is a blog not a news source. I wish more people would realize that.

...

News for Nerds. Stuff that matters.

O.K., I'll bite, what part of that line do you not understand? If /. billed itself as a "blog" then I'd understand your point. However, /. is a corporate based, self-billed "News" site. Whether reader submission driven or not, it is a news site. You are wrong. But, thanks for your thoughts.