Access Global Variable.

[gothic_coder]

I have been asked this question in my recent interview... "How can we make sure that only one thread access global variable?" What's the appropriate answer. Thanks all

[CPallini]

Using "Synchronization". :)

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[rp_suman]

Mutex Objects

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[ThatsAlok]

rp_suman wrote:

Mutex Objects

Critical section at the time of accessing of the variable! not mutex if we talking about thread! mutex is more beneficial in case of limiting access across different process

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[Aescleal]

The first response is to gently chide the interviewer telling him (or her) that they're mad for using global variables in a multi-threaded program. Once they've made some excuse for using global data (legacy code, have to make change immediately otherwise the four horsemen ride, Jormangand wakes or even worse the company's stock price falls) the second thing to do is turn the question around and ask whether they mean from one thread at a time or only from one thread? If they say from only one thread EVER then say you'd use thread local storage (TLS) or refactor the code to pass the parameter down the call stack from the function the thread started in. If they "from one thread at a time" say you'd use the appropriate type of lock - usually a type of mutex. The final thing before the interviewer moves on is to ask whether programmers use a lot of globals at this company... If they do consider asking for more money as you'll need it for the extra hours spent debugging gash code (and yes, this is from recent personal experience...) Cheers, Ash

[gothic_coder]

Thanks guys, Synchronization is what i replied, But as Aescleal get it right the interviewer was asking that the variable must be accessed only and only by one thread.. So i guess the TLS is the answer he wants, I need to see these thing in deep :) Nevertheless i got the job :)

[Luc Pattyn]

That does not limit the number of threads accessing a variable, it merely sequences the accesses, making sure they don't overlap. :)

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[CPallini]

Of course. It wasn't clear to me what the interviewer really asked to the OP. BTW you may use a synchronization object to prevent other threads accessing the resource, if hanging the other threads is an option... :-D

If the Lord God Almighty had consulted me before embarking upon the Creation, I would have recommended something simpler. -- Alfonso the Wise, 13th Century King of Castile.
This is going on my arrogant assumptions. You may have a superb reason why I'm completely wrong. -- Iain Clarke
[My articles]

modified on Thursday, June 17, 2010 8:40 AM

[Luc Pattyn]

We both read the same sentence, which is pretty clear IMO. I took it as is, you chose to read something that wasn't really there... Hanging is not an option, this ain't 19th century Texas. :)

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[CPallini]

Yes, indeed it was pretty clear and I really chose to read it that way (I've updated my previous reply). Hanging threads is an everyday option for many 'senior developers' around... :-D

If the Lord God Almighty had consulted me before embarking upon the Creation, I would have recommended something simpler. -- Alfonso the Wise, 13th Century King of Castile.
This is going on my arrogant assumptions. You may have a superb reason why I'm completely wrong. -- Iain Clarke
[My articles]

[Luc Pattyn]

:thumbsup:

Luc Pattyn [Forum Guidelines] [Why QA sucks] [My Articles] Nil Volentibus Arduum

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