Make sure threads are handled correctly for the REST API

[CasperWA]

No description provided.

[giovannipizzi]

I imagine this is related to #3708, and means applying the changes for the REST API?
I can confirm that I am using the REST API on a Django profile, using the materials cloud feature "browse your own explore section". After a few clicks, I get 500 errors and if I go directly to the REST API, I get

{"message":"QueuePool limit of size 5 overflow 10 reached, connection timed out, timeout 30 (Background on this error at: http://sqlalche.me/e/3o7r)"}

(AiiDA develop branch commit 617b2df)

@CasperWA is this something that can be investigated, maybe with the help of @asle85 ?
We wanted to use the REST API for the tutorial on Wannier90+AiiDA on March 25th, but if there is this problem I fear this is not usable...

[ltalirz]

Just ran into this issue myself as well...

[CasperWA]

Just ran into this issue myself as well...

"Good" to hear... I'm still creating a test to reproduce it locally and eventually make sure my fix works as intended.

[ltalirz]

hooray!
thanks @CasperWA and @sphuber !