[ganesh][dawn] Better handle buffer mapAsync failures
GrDawnGpu tries to guarantee the CPU mapping invariants of GrDawnBuffer
objects that are managed by a GrStagingBufferManager by issuing and
tracking mapAsync requests following command buffer submission. However,
this logic suffered from some issues where:
1. The code always assumed mapAsync succeeds. If a mapAsync request
failed during shutdown due to a lost GPU connection, the GrDawnGpu
destructor would spin forever waiting for pending mapAsync requests
to complete.
2. If a client unmapped and then re-mapped a buffer that isn't managed
by the async staging buffer logic in GrDawnGpu, the buffer would
never get mapped and likely hit an assertion for a non-staging
buffer.
These are now fixed:
* GrDawnBuffer now has more explicit error handling to make it more
tolerant to mapAsync failures.
* GrGpuBuffer now relies on mapAsync completion callbacks instead of
spinning on `GrGpuBuffer::isMapped` as a buffer may never get mapped
in the case of an error. This also has the benefit of tracking the
mapAsync procedure state on a per-request basis intead of relying on
state stored in GrDawnBuffer. The existing `fBusyStagingBuffers` has
been replaced by a single reference counted `GrDawnAsyncWait` object.
* A synchronous/blocking map function has been provided to satisfy the
`GrGpuBuffer::onMap` contract. This method is not used in the existing
staging buffer use cases in practice but it solves part of problem #2
above.
* GrDawnGpu::onReadPixels now uses a GrDawnBuffer's blocking map
functionality using the public GrGpuBuffer API. This has the same
behavior as the existing blocking map that created and mapped a
wgpu::Buffer directly.
* The invariants around GrDawnBuffer lifetime and CPU mapping are
documented in class level comments.
Bug: skia:12512
Change-Id: I8bb92137fbd60c31066e4071bd696018b3563bb8
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/533758
Reviewed-by: Greg Daniel <egdaniel@google.com>
Commit-Queue: Arman Uguray <armansito@google.com>
7 files changed
