Save and export only use a single thread
GIMP version: Tested on 3.10 and 2.99
Operating System: Tested on Arch and Xubuntu 18.04
Priority: Very high (Personal opinion)
Description of the bug
When you save or export a file, Gimp only uses a single thread. A 100+Mb file can take up to an entire minute to be processed.
Reproduction
Is the bug reproducible? Always
Reproduction steps:
1.Create a Gimp file with 500-1000 layers filled with images.
2.Try to save or export the file.
Expected result: All threads participate in the process. Fast save/export.
Actual result: Only one thread is used. Takes up to a minute to save/export.