Re: Java processors

Lew <>
Fri, 6 Jul 2012 14:17:40 -0700 (PDT)
Gene Wirchenko wrote:

Roedy Green wrote:

Eric Sosman wrote, quoted or indirectly quoted someone who said :

If you just dove in and started
interpreting you might be running more slowly, but you'd have a
head start

That is just what JITs do. It is only after a while they have gathered
some stats to they decide which classes to turn to machine code. The
astounding thing is they stop the interpreter in mid flight executing
a method, and replace it with machine code and restart it. That to me
is far more impressive than walking on water.

They don't do that exactly. There's no restart.


     Do you have a cite [sic] for that? Restarting a method could be messy.

This was in the links I provided upthread.

Imagine if files are opened, other objects created, etc.

     I suspect that it might be as prosaic as a method execution times
counter reaching a threshold value triggering the conversion.

Also cited upthread. I don't know that it's method-by-method; I
think HotSpot optimizes at finer granularity than that. The cited
reference refers to optimizing "loops".

But it's far from prosaic. The HotSpot compiler (not to be confused with
other JIT compilers) can switch to native-compiled code mid-execution
while the interpreted code is running. Given that the compiler is
aware of run-time circumstances, I don't know that it would need to
have trouble with file handles and the sorts of things you mention.


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