[pypy-dev] Thinking about the GIL

Timothy Baldridge tbaldridge at gmail.com
Wed Mar 16 14:13:06 CET 2011

> one alternative approach is to have a separate VM in each thread.  Then pass
> messages between them.  Works well, and no GIL in each VM.  You have to have
> clean code that allows you to have a separate VMs in a process.  However,
> it's easier to make your code be able to run in separate VMs, than to recode
> it to allow concurrent thread access to all data structures.  This way is
> easier to implement than removing a GIL.

This is what Erlang does, but unfortunately it scales very poorly when
 you have large datasets (as mentioned above). If you want 4 threads
pounding on 1GB of data, either they need to ask a 5th thread for each
data item, or each thread needs its own copy of that 1GB dataset. Even
embarrassingly parallel things such as raytracing are very hard in
this model.


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