Volatile Write around Sequence field

[alexandrnikitin]

No description provided.

[alexandrnikitin]

@lust4life, WDYT about this fix? When we just Volatile.Write around the Sequence field.

[lust4life]

        [StructLayout(LayoutKind.Explicit, Size = 16, CharSet = CharSet.Ansi)]
        private struct Cell
        {
            [FieldOffset(0)]
            public int Sequence;
            [FieldOffset(8)]
            public object Element;

hi @alexandrnikitin , do we need this explicit structlayout in cell struct ? how about leave the compile generate for it (so it can be auto aligned)?

[alexandrnikitin]

Same reason as with var buffer = _buffer; in enqueue/dequeue. We always read Sequence first. If it's on the edge of a cache line, then hopefully prefetch can help with Element. But it's my speculation mostly, I don't have enough evidence. It's not visible in microbenchmarks as everything in L1 already.

When JIT alignes it puts Element first:

Type layout for 'CellAuto'
Size: 16 bytes. Paddings: 4 bytes (%25 of empty space)
|=================================|
|   0-7: Object Element (8 bytes) |
|---------------------------------|
|  8-11: Int32 Sequence (4 bytes) |
|---------------------------------|
| 12-15: padding (4 bytes)        |
|=================================|


Type layout for 'CellLayoutKindExplicit'
Size: 16 bytes. Paddings: 4 bytes (%25 of empty space)
|=================================|
|   0-3: Int32 Sequence (4 bytes) |
|---------------------------------|
|   4-7: padding (4 bytes)        |
|---------------------------------|
|  8-15: Object Element (8 bytes) |
|=================================|

[lust4life]

get it , thanks. 👍