blosc.set_nthreads() not working

[ali-arbabian]

Hi all,
Having an issue where blosc.set_nthreads() and blosc.set_releasegil() are not actually changing the arguments inside the blosc package.
I'm checking blosc.nthreads and it stays at 8 despite the blosc.n_threads() call. I've also tried moving these lines to the top of my first entry script, still no luck.

Steps to reproduce:

import blosc   
blosc.set_nthreads(12)
blosc.set_releasegil(True)
print(blosc.print_versions())
print("nthreads: ", blosc.nthreads)

Output:

python-blosc version: 1.10.2
Blosc version: 1.21.0 ($Date:: 2020-12-22 #$)
Compressors available: ['blosclz', 'lz4', 'lz4hc', 'zlib', 'zstd']
Compressor library versions:
  BloscLZ: 2.3.0
  LZ4: 1.9.3
  Zlib: 1.2.8
  Zstd: 1.4.8
Python version: 3.7.3 (default, Mar 27 2019, 22:11:17) 
[GCC 7.3.0]
Platform: Linux-4.15.0-91-generic-x86_64 (#92-Ubuntu SMP Fri Feb 28 11:09:48 UTC 2020)
Linux dist: Ubuntu 18.04.4 LTS
Processor: x86_64
Byte-ordering: little
Detected cores: 80
Number of threads to use by default: 8
-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
None
nthreads:  8

[esc]

@ali-arbabian thank you for reporting this! I have encountered this in Bloscpack too but have not gotten around to debugging it further. The following issue in Bloscpack:

Blosc/bloscpack#96

... I believe actually has it's root cause in this python-blosc bug you have reported here! I also believe this may have been broken for some time now(years?) but not sure about the exact python-blosc version where this regression was introduced . I would also consider this bug to be of reasonably high severity since it severly limits the usefulness and flexibility of the package.

[FrancescAlted]

Thanks for bringing this to our attention. We will try to fix this soon. As always, if you find a solution/workaround, this would help us in accelerating the fix.

[ali-arbabian]

Thanks for bringing this to our attention. We will try to fix this soon. As always, if you find a solution/workaround, this would help us in accelerating the fix.

Sounds good! I will look into this issue again this weekend if I get the chance.
Also just to clarify something in my original post, I'm not sure if blosc.set_releasegil() is working or not as there is no function to check the current releasegil state in blosc.

[ali-arbabian]

Any updates on this issue?

[FrancescAlted]

Ups, thanks for the reminder. The code worked fine, but internally we did not update the global nthreads variable. This should be fixed now.

[esc]

I can confirm this works:

In [1]: import blosc

In [2]: blosc.set_nthreads(1)
Out[2]: 8

In [3]: blosc.nthreads
Out[3]: 1

In [4]: blosc.__version__
Out[4]: '1.10.3.dev0'

Previously:

In [1]: import blosc

In [2]: blosc.set_nthreads(1)
Out[2]: 8

In [3]: blosc.nthreads
Out[3]: 8

In [4]: blosc.__version__
Out[4]: '1.10.2'

This is great @FrancescAlted -- would we be able to get a new release to that I can close Blosc/bloscpack#96 -- who do I ask these days?