memory location of static variables?

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Fuzzy - 19 Jan 2004 05:51 GMT

Does anyone have any insight into how .NET physically stores static
variables?

In a performance critical section of my application, I'm considering
caching some often calculated values where there is a high probability
of input values remaining the same between successive calls.

The cost of recaluation is not huge, but it would be quicker to check
if current input value is the same as the previous input value - if
so, just return previous calculated value.

However, I would have to store these previous values in a static
member variable. If this caused a processor cache miss or soft page
fault, it would obviously be faster to just recalculate the return
value.

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David Notario [MSFT] - 20 Jan 2004 07:20 GMT

The best answer, as always, is to measure.

In released x86 versions of the CLR, normal statics (ie, per appdomain
statics) are stored in a fixed block of memory that the code can directly
reference, so retrieving them is one instruction (mov [address]) for
primitive types and 2 instructions for GC and valuetypes (valuetypes are
stored in boxed form).

For appdomain shared code (ASP.NET), static access is slower, as we have to
get to this statics block via an appdomain based indirection.

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David Notario
Software Design Engineer, CLR JIT Compiler
http://devdiary.xplsv.com

> Does anyone have any insight into how .NET physically stores static
> variables?
[quoted text clipped - 11 lines]
> fault, it would obviously be faster to just recalculate the return
> value.

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Dmitry Kostenko - 10 Feb 2004 17:06 GMT

Does this 'per AppDomain indirection' work if use two AppDomains in Windows Forms application and use LoaderOptimization.SingleDomain
Does this indirection work is there are no shared assemblies among domains (except corlib)?

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Ori Gershony [MSFT] - 20 Feb 2004 22:33 GMT

This optimization applies only when we don't generate domain neutral code
(i.e. code that can be used in multiple appdomains). When we generate
domain neutral code, the same code needs to execute in multiple appdomains,
which means that the specific statics that it accesses can be different
depending on the appdomain that it executing in.

When using LoaderOptimization.SingleDomain, the CLR will JIT multiple
copies of the code, and so each one will be optimized for the static
accesses of its specific appdomain. Ofcourse the cost you are trading off
here is having multiple copies of the code.

As with anything else, I encourage you to measure your specific scenarios
to understand the sources of overhead and areas to focus on.

-- Ori.

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>Subject: Re: memory location of static variables?
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>Does this 'per AppDomain indirection' work if use two AppDomains in Windows Forms application and use LoaderOptimization.SingleDomain?

Does this indirection work is there are no shared assemblies among domains
(except corlib)?

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memory location of static variables?

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