Reason for revert:
bust the roll
Original issue's description:
> SkOnce: 2 bytes -> 1 byte
>
> This uses the same logic we worked out for SkOncePtr to reduce
> the memory footprint of SkOnce from a done byte and lock byte
> to a single 3-state byte:
>
> - NotStarted: no thread has tried to run fn() yet
> - Active: a thread is running fn()
> - Done: fn() is complete
>
> Threads which see Done return immediately.
> Threads which see NotStarted try to move to Active, run fn(), then move to Done.
> Threads which see Active spin until the active thread moves to Done.
>
> This additionally fixes a too-weak memory order bug in SkOncePtr,
> and adds a big note to explain.
>
> BUG=skia:
> GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1904483003
>
> Committed: https://skia.googlesource.com/skia/+/df02d338be8e3c1c50b48a3a9faa582703a39c07TBR=herb@google.com
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=skia:
Review URL: https://codereview.chromium.org/1898413004
This uses the same logic we worked out for SkOncePtr to reduce
the memory footprint of SkOnce from a done byte and lock byte
to a single 3-state byte:
- NotStarted: no thread has tried to run fn() yet
- Active: a thread is running fn()
- Done: fn() is complete
Threads which see Done return immediately.
Threads which see NotStarted try to move to Active, run fn(), then move to Done.
Threads which see Active spin until the active thread moves to Done.
This additionally fixes a too-weak memory order bug in SkOncePtr,
and adds a big note to explain.
BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1904483003
Review URL: https://codereview.chromium.org/1904483003
The API and implementation are very much simplified.
You may not want to bother reading the diff.
As is our trend, SkOnce now uses <atomic> directly.
Member initialization means we don't need SK_DECLARE_STATIC_ONCE.
SkSpinlock already works this same way.
All uses of the old API taking an external bool* and Lock* were pessimal,
so I have not carried this sort of API forward. It's simpler, faster,
and more space-efficient to always use this single SkOnce class interface.
SkOnce weighs 2 bytes: a done bool and an SkSpinlock, also a bool internally.
This API refactoring opens up the opportunity to fuse those into a single
three-state byte if we'd like.
No public API changes.
TBR=reed@google.com
BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1894893002
Review URL: https://codereview.chromium.org/1894893002
This enables removing the more complicated atomic shims from SkAtomics.h.
TBR=reed
This doesn't actually change any API.
CQ_EXTRA_TRYBOTS=client.skia:Test-Ubuntu-GCC-GCE-CPU-AVX2-x86_64-Release-TSAN-Trybot,Test-Ubuntu-GCC-Golo-GPU-GT610-x86_64-Release-TSAN-Trybot
Review URL: https://codereview.chromium.org/1867863002
- Use std::atomic directly.
- No more need for SkPODSpinlock or SK_DECLARE_STATIC_SPINLOCK.
Now simple code like this works as you'd hope:
static SkSpinlock gLock;
That is, it starts unlocked and there's no static initializer.
std::atomic_flag would make this terser and standard-guaranteed,
but ATOMIC_FLAG_INIT caused not-yet-implemented errors on MSVC 2013.
The generated code for this approach is identical.
It appears the implicit constructor is constexpr when all the member
initializers are. I'm hoping this way of producing constexpr constructors
without typing "constexpr" gives us a way to eliminate more SkFoo / SkBaseFoo
distinctions and SK_DECLARE_STATIC_FOO. This was certainly the easiest.
BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1734383002
Review URL: https://codereview.chromium.org/1734383002
