After looking into task isolation issues with Sergey, we couldn't find the
reason behind the deadlocks that we are getting in T87938 and a Sprite Fright
file involving motion blur renders.
There is no apparent place where we adding or waiting on tasks in a task group
from different isolation regions, which is what is known to cause problems. Yet
it still hangs. Either we do not understand some limitation of TBB isolation,
or there is a bug in TBB, but we could not figure it out.
Instead the idea is to use isolation only where we know we need it: when
holding a mutex lock and then doing some multithreaded operation within that
locked region. Three places where we do this now:
* Generated images
* Cached BVH tree building
* OpenVDB lazy grid loading
Compared to the more automatic approach previously used, there is the downside
that it is easy to miss places where we need isolation. Yet doing it more
automatically is also causing unexpected issue and bugs that we found no
solution for, so this seems better.
Patch implemented by Sergey and me.
Differential Revision: https://developer.blender.org/D11603
* USD and OpenVDB headers use deprecated TBB headers, suppress all deprecation
warnings there since we have no control over them.
* For our own TBB includes, use the individual headers rather than the tbb.h that
includes everything to avoid warnings, rather than suppressing all.
This is in anticipation of the TBB 2020 upgrade in D10359. Ref D10361.
Add TBB::flow graph scheduling to BLI_task.
Using flow graphs, a graph of nodes (tasks) and links can be defined.
Work can flow though the graph. During this process the execution of the nodes will be
scheduled among the available threads.
We are planning to use this to improve the threading in the draw manager.
The implemented API is still limited it only supports sequential flows. Joins and buffers
are not supported. We could eventually support them as part of an CPP API. These features
from uses compile time templates and are hard to make a clean C-API for this.
Reviewed By: Sergey Sharybin, Brecht van Lommel
Differential Revision: https://developer.blender.org/D7578
