[Vm-dev] Sista alternate bytecodes + Java Bytecode ?

[Raffaello Giulietti]

Hi Ben,

in addition to Clément's observations, you should not forget that much 
existing JVM bytecode depends on the multi-threading capabilities of any 
contemporary JVM implementation and its supporting platform libraries 
(e.g., java.util.concurrent.* for concurrency frameworks, 
java.util.stream.* for parallel streams, etc.)

So, besides the humongous work mentioned by Clément, I can only imagine 
how hyper-humongous a work would it be to make the current OpenSmalltalk 
VM multi-threaded to accommodate the JVM computational model inherent in 
almost any real-world Java bytecode. Think only of the impact on the 
garbage collectors, for example. (Or on how to present multi-threading 
to Smalltalkers accustomed to the vastly simpler shared memory model of 
Process, where the happens-before relationship is trivial.)



Greetings
Raffaello




On 2017-10-17 16:12, Raffaello Giulietti wrote:
> Hi,
> 
> That question should be asked on vm-dev.
> 
> Just a detail, multibytecode set support is prior to the Sista
> implementation, it was used for example in the context of Newspeak (Squeak
> and Newspeak bytecodes supported together). Sista uses that feature, which
> makes it look like new in the Pharo community since afaik no one used it
> before in the context of Pharo.
> 
> Then yes it is feasible to have the VM process Java bytecode, but it's
> humongous work. On the top my head, we would need to support typed
> bytecodes for Numbers and exceptions at the bytecode level (which in itself
> is month of work, imagine raising an exception from Java/ST and catch it
> from the other runtime, with multiple ensure/try finally in between)
> 
> Note that supporting the Java bytecode is far from enough to be able to run
> Java code (We also need core Java libraries support at least, including
> exceptions/stack reification model that should be able to interact with
> each other)
> 
> You can have a look at Smalltalk/X where the VM can run Java, C and
> Smalltalk.
> 
> Regards
> 
> 
> On Tue, Oct 3, 2017 at 1:57 PM, Ben Coman <btc at openinworld.com> wrote:
> 
>  > Just wondering about an exotic idea, with Sista facilitating alternate
>  > bytecodes (btw, is that multiple bytecode sets within one Image?), how
>  > feasible would it be to have the VM process Java bytecode?
>  >
>  > cheers -ben
>  >
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