Re: [ljc] Concurrency, multi-threaded programming: under the hood

From: Abraham Marín P.
Sent on: Saturday, March 16, 2013 6:54 PM
Hi all,

I do share Wes's cynicism, I've seen cases when some supposedly senior and experience developers suggest to fix a performance problems by throwing in 100 threads... in a dual-core machine. In my experience most concurrency advocates don't really understand how multi-threading works and they just see it as a silver bullet to enhance performance; when eventually the overhead is so high that the additional threads actually decreases performance they blame the more junior developer for "having introduced bugs and created deadlocks".

On the other hand, there is one interesting point in Barry's email:

- Why are some developers drawn to this deeper level and why do some people seem to grasp these concepts so easily against others? 

I think this is down to each individual's abstraction capabilities, and maybe to a lesser degree to education. To me, truly understanding concepts like multi threading or pointers (specially the raw pointers in C/C++) is a bit like understanding mathematics: some people get it naturally, and some others spend hours and hours and still they don't. You can teach and teach, but some people will just never get it.

Cheers,
Abraham



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Abraham Marín Pérez

Twitter: @AbrahamMarin
LinkedIn: http://lnkd.in/TTHC8W

Sent from my iPhone

On 16 Mar 2013, at 17:14, Wesley Hall <[address removed]> wrote:

Hi Barry, 

Interestingly enough, if I am talking to a company that continually stresses the need for concurrency skills, then it is actually a little bit of a red-light. That depends a bit on the company, because some people are solving problems where concurrency is a fundamental part of the problem, where it is not, a major focus on this as a topic actually screams something like, "We are in a real mess, we have built this system, hadn't considered multi-user testing, now discovered that it doesn't scale, and have decided to try to throw hardware at the problem!". 

That probably isn't all that helpful, so I will try to improve upon that...

In my view, a *good* answer to the, "how well do you know Java concurrency?" question is this...

"I am familiar with the java.util.concurrent classes, and I have read 'Java concurrency in practice', generally though, I find that if you maintain good design fundamentals, lean strongly towards immutability, which is a practice that has other advantages too, and isolate concurrency management in specific areas so that the vast majority of the code-base can be written without reference to concurrency techniques, then concurrency problems becomes far easier to solve. Writing custom concurrency code is a difficult and time-consuming task, and the cost of ownership of concurrency management code is much higher so it is also important to make sure other techniques are considered, with the requirements in mind, of course"

It can also be the case that, when people talk about concurrency they are really referring to problems like transaction isolation and database locking, which is a much more complicated topic in my opinion. They may also have other performance tuning techniques in mind. What might be being said here is, "We have found ourselves in a bit of a mess (which may or may not be self-inflicted), to get out of it, what we really need is a highly experienced and expensive software architect, but getting funding for that would require us to admit our problems, so we are trying to disguise this hire in the form of simply expanding the development team". This problem, I don't really know how to solve.... 

I know that some of that sounds pretty cynical, and I am quite open to be told, "You are wrong! That's not how it works at all!!", but I have this little feeling that some of my developer friends reading this might just be nodding along in silent agreement, and excessive honesty can be a flaw of mine at times ;)

For your purposes, if you have a candidate going for a role that has concurrency as a top level requirement, ask them if they have read, "Java concurrency in practice", and if they have not, advise strongly that they do, since it should give them the tools to answer some of the more tricky questions, and then.... pray for them ;)

Wes



On Sat, Mar 16, 2013 at 2:36 PM, Barry Cranford <[address removed]> wrote:
Hi all,

We are often tasked to find Java developers with an understanding of low level core Java. Not necessarily specialist contractors at 5-600 pday, but permanent developers, one may classify as mid-senior level (40-60k). When pushed this is often defined by developers that understand what is going on 'under the hood' e.g. not just how to use popular frameworks but those that understand the concepts and principles beneath them. Whilst some companies will be a little more easy on practical experience, they will push for an understanding. 

Many developers don't make it through interview processes with feedback coming up time and again around a lack of understanding of multi threaded programming and concurrency. I have seen a few conversations recently on the list around these areas so I'm keen to understand the thoughts of the community on this. 

A few things I'm curious about...

- If we could put on some deep dive talks what subjects would you personally most like to have covered?
- Why are some developers drawn to this deeper level and why do some people seem to grasp these concepts so easily against others? 
- If you could offer advice to students starting out in Java development today, how would you suggest learning the fundamentals of these concepts? (reading, self study, projects, talks, oss, something else)?
- Have you been through this learning process in the past and had a eureka moment? What happened for you personally.

If you have any opinions on any of the above please feel free to reply to me personally at [address removed] or through the list. 

Enjoy your weekend!

Kind regards,
Barry




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