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Document GenericMemory and AtomicMemory #54642

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Document GenericMemory and AtomicMemory #54642

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Document GenericMemory and AtomicMemory
oscardssmith May 31, 2024
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update docs to refrence intrinsics until there is an actual stable in…
oscardssmith Jun 4, 2024
2189584
Update base/genericmemory.jl
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32 changes: 27 additions & 5 deletions base/genericmemory.jl
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Expand Up @@ -3,9 +3,21 @@
## genericmemory.jl: Managed Memory

"""
GenericMemory{kind::Symbol, T, addrspace=Core.CPU} <: AbstractVector{T}
GenericMemory{kind::Symbol, T, addrspace=Core.CPU} <: DenseVector{T}

One-dimensional dense array with elements of type `T`.
Fixed-size [`DenseVector{T}`](@ref DenseVector).
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Fixed-size [`DenseVector{T}`](@ref DenseVector).
A [`DenseVector{T}`](@ref DenseVector). Fixed-size, in the sense that the length of a value of this type doesn't change after construction.

Maybe it'd be better to be more precise regarding "fixed-size"?

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I don't really see this is clearer. Is there an ambiguity with the original version? Would "constant length" be clearer?

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@nsajko nsajko Jun 5, 2024 •
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Perhaps the current version is OK. My motivation is to avoid confusion with the StaticArrays.jl-sense of "constant length", where the length is in the type domain.


`kind` can currently be either `:not_atomic` or `:atomic`. For details on what `:atomic` implies, see [`AtomicMemory`](@ref)

`addrspace` can currently only be set to Core.CPU. It is designed to to permit extension by other systems
such as GPUs, which might define values such as:
```
module CUDA
const Generic = bitcast(Core.AddrSpace{CUDA}, 0)
const Global = bitcast(Core.AddrSpace{CUDA}, 1)
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@jakobnissen jakobnissen Jun 3, 2024 •
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const Generic = bitcast(Core.AddrSpace{CUDA}, 0)
const Global = bitcast(Core.AddrSpace{CUDA}, 1)
const Generic = Core.AddrSpace{CUDA}(0x00)
const Global = Core.AddrSpace{CUDA}(0x01)

This code doesn't work since a) bitcast is not public, and b) the integer must be a 1-byte integer for bitcast to work

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I think this was unresolved with the force push.

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oops. Will re-resolve once #54681 merges.

end
```
The exact semantics of these other addrspaces is defined by the specific backend, but will error if the user is attempting to access these on the CPU.

!!! compat "Julia 1.11"
This type requires Julia 1.11 or later.
Expand All @@ -15,7 +27,7 @@ GenericMemory
"""
Memory{T} == GenericMemory{:not_atomic, T, Core.CPU}

One-dimensional dense array with elements of type `T`.
Fixed-size [`DenseVector{T}`](@ref DenseVector).

!!! compat "Julia 1.11"
This type requires Julia 1.11 or later.
Expand All @@ -25,8 +37,18 @@ Memory
"""
AtomicMemory{T} == GenericMemory{:atomic, T, Core.CPU}

One-dimensional dense array with elements of type `T`, where each element is
independently atomic when accessed, and cannot be set non-atomically.
Fixed-size [`DenseVector{T}`](@ref DenseVector).
Access to its any of its elements is performed atomically (with `:monotonic` ordering).
Setting any of the elements must be accomplished using the `@atomic` macro and explicitly specifying ordering.

!!! warning
Each element is independently atomic when accessed, and cannot be set non-atomically.
Currently the `@atomic` macro and higher level interface have not been completed,
but the building blocks for a future implementation are the internal intrinsics
`Core.memoryrefget`, `Core.memoryrefset!`, `Core.memoryref_isassigned`, `Core.memoryrefswap!`,
`Core.memoryrefmodify!`, and `Core.memoryrefreplace!`.

For details, see [Atomic Operations](@ref man-atomic-operations)
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!!! compat "Julia 1.11"
This type requires Julia 1.11 or later.
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1 change: 1 addition & 0 deletions doc/src/base/arrays.md
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Expand Up @@ -30,6 +30,7 @@ Base.StridedArray
Base.StridedVector
Base.StridedMatrix
Base.StridedVecOrMat
Base.GenericMemory
Base.Memory
Base.memoryref
Base.Slices
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