This adds sk_memory_barrier(), implemented using sk_atomic_fetch_add() on an uninitialized variable. If that becomes a problem we can drop this to the porting layer, using std::atomic_thread_fence() / __atomic_thread_fence() / __sync_synchronize().
The big win is that ref() doesn't generate a memory barrier any more on ARM.
This is an instance of SkSafeRef() in SkPaint(const SkPaint&) after this CL:
4d0: 684a ldr r2, [r1, #4]
4d2: 6018 str r0, [r3, #0]
4d4: b13a cbz r2, 4e6 <_ZN7SkPaintC1ERKS_+0x2e>
4d6: 1d10 adds r0, r2, #4
4d8: e850 4f00 ldrex r4, [r0]
4dc: 3401 adds r4, #1
4de: e840 4500 strex r5, r4, [r0]
4e2: 2d00 cmp r5, #0
4e4: d1f8 bne.n 4d8 <_ZN7SkPaintC1ERKS_+0x20>
Here's the before, pretty much the same with two memory barriers surrounding the ref():
4d8: 684a ldr r2, [r1, #4]
4da: 6018 str r0, [r3, #0]
4dc: b15a cbz r2, 4f6 <_ZN7SkPaintC1ERKS_+0x3e>
4de: 1d10 adds r0, r2, #4
4e0: f3bf 8f5f dmb sy
4e4: e850 4f00 ldrex r4, [r0]
4e8: 3401 adds r4, #1
4ea: e840 4500 strex r5, r4, [r0]
4ee: 2d00 cmp r5, #0
4f0: d1f8 bne.n 4e4 <_ZN7SkPaintC1ERKS_+0x2c>
4f2: f3bf 8f5f dmb sy
The miscellaneous files in here are just fixups to explicitly include SkMutex.h,
instead of leeching it off SkRefCnt.h.
No public API changes.
TBR=reed@google.com
Build trybots seem hosed.
NOTRY=true
BUG=skia:
Review URL: https://codereview.chromium.org/896803002
7b274c78fb