Ruby Fiddle and Global Interpreter Lock (GIL)

Question

I am using Fiddle to call an external C Function for some heavy linear algebra calculations (Mac OSX).

The module definition looks like

  module BLAS
    extend Fiddle::Importer
    dlload $BLAS_PATH
    extern 'void cblas_dgemm(int, int, int, int, int, int, double, double*, int, double*, int, double, double*, int)'
    extern 'void cblas_dgemv(int, int, int, int, double, double*, int, double*, int, double, double*, int)'
.......

The libraries have been optimized for mac osx and can use all the cores available. Unfortunately when I call these functions from Ruby with Fiddle only one core is used and my understanding is that this happens because of the GIL.

Is there a way to release the lock during the execution of external functions?

I am using ruby 2.0.0-p247 (not the system Ruby).

I just noticed that Fiddle releases the gil in ruby 2.3 - if you can update ruby that is probably the easiest solution — Frederick Cheung, May 18 '16 at 14:11

Frederick Cheung · Accepted Answer · 2016-05-18T13:13:45.860

In ruby 2.3 this is the default (see the issue on the ruby bug tracker).

Prior to that, it doesn't look like it was exposed in the Fiddle api. There is a function in the ruby c API called rb_thread_call_without_gvl that does pretty much exactly what it says on the tin: it releases the gvl, calls the passed function, reacquires the gvl and returns. It's a little tricky to use - be sure to read the comments in thread.c.

If you can't upgrade, I suspect your best bet is to write a very thin C layer that wraps calls with rb_thread_call_without_gvl and then use fiddle to call that wrapper library.

Ruby Fiddle and Global Interpreter Lock (GIL)

1 Answers1

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