Change HazptrHoler try_protect memory fence from light to heavy #2522
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The protected pointer placed in hprec_ (store) should not be reordered after to read hazptr_obj (load). folly::asymmetric_thread_fence_light on Linux only prevents compiler reordering, but cannot prevent CPU reordering (x86 allows store-load reorder). Therefore the load operation may be executed first but the protected pointer has not yet placed to hprec_, if there some other threads try to retire this hazptr, it might be success.
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The protected pointer placed in hprec_ (
store) should not be reordered after to read hazptr_obj (load).folly::asymmetric_thread_fence_lighton Linux only prevents compiler reordering, but cannot prevent CPU reordering (x86 allowsstore-loadreorder).Therefore the load operation may be executed first but the protected pointer has not yet placed to hprec_, if there some other threads try to retire this
hazptr, it might be success.