On Mon, 3 Jan 2011 08:01:35 +0000, Tamas Rudnai wrote:

> What they should do is to compile the code when installing the
> software and job is done. Maybe installation would be much slower, so
> they could cache the binaries of the most popular platforms to help on
> it -- so then they are slowly going back to the traditional cross
> compilation procedure what Linux is doing today :-)

I believe the MS JIT compiler compiles a method at a time; the hit is
taken the first time the method is called.  There are pre-compilers,
such as ngen, that allow you to pre-compile, but they don't tend to be
used - the main way I've seen them used is for pre-compiling high-volume
websites so that the first hit doesn't trigger a huge JITting spree and
load the server down.

Pre-compiling at installation time is very suboptimal; you lose the
benefit of software upgrades to the JIT compiler, which could result in
tighter or more secure code being generated, etc.  You would have to
install everything, too - no good for plugins and the like, where you
should just be able to 'xcopy' deploy DLLs.  And you are also left with
a sub-optimal executable image if you were to change your processor or
other hardware.  Not to mention support for generics would be difficult,
if at all possible in their current incarnation.

In theory, the JIT compiler could also change its already-compiled code
on the fly if metrics showed that there would be more suitable
optimisations to apply for the pattern of execution.  I'm not aware of
this actually happening, but I seem to remember reading some MS
documentation a while ago that was flinging all sorts of cool
possibilities about.

Regards,

Pete Restall

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