at-sync macro is barely documented #49921
Description
The @sync macro is not mentioned anywhere in the page Multi-Threading, while in Multi-processing and Distributed Computing it's mentioned casually in the first section, without explaining what it is. In the multiprocessing page there are a couple of examples which use the macro, but without any explanation. At least the macro has a docstring, but figuring out what it does and when it should be used from the prose manual is quite hard, to say the least.