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Funny way how to get thread specific id [message #7642]

Fri, 12 January 2007 11:07

mirek
Messages: 14291
Registered: November 2005

Ultimate Member

Sometimes it could be useful to test quickly for thread specific id.

For example, if you are incrementing reference count, it seems to be possible to store thread specific id somewhere and then perform non-atomic increment if they match. (Disclaimer: MAYBE. I do not say it is really possible, it is just my current research subject).

Today I have found a nice and simple way how to obtain such id:

__thread int x;

&x is your ID Wink

It is pretty fast too, because TLS pointers are stored in register (in fact, in gs segment on x86).

Mirek

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Re: Funny way how to get thread specific id [message #7655 is a reply to message #7642]

Fri, 12 January 2007 23:46

gprentice
Messages: 260
Registered: November 2005
Location: New Zealand

Experienced Member

That reminds me of this (non thread-safe) code and bug in VC7. I don't have the latest version of VC to see if it's been fixed.

[edit] URL didn't seem to work, try this
http://tinyurl.com/y4otk6

Graeme

[Updated on: Fri, 12 January 2007 23:50]

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Re: Funny way how to get thread specific id [message #7656 is a reply to message #7655]

Sat, 13 January 2007 00:08

mirek
Messages: 14291
Registered: November 2005

Ultimate Member

Yes, I have noticed this behavior too... Since them I simply do not rely on statics inside templates to be unique...

(In this case, planned possible use was within single .cpp file).

Mirek

[Updated on: Sat, 13 January 2007 00:08]

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