483 lines
14 KiB
Julia
483 lines
14 KiB
Julia
# This file is a part of Julia. License is MIT: https://julialang.org/license
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using Core.Intrinsics: llvmcall
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import Base: setindex!, getindex, unsafe_convert
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import Base.Sys: ARCH, WORD_SIZE
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export
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Atomic,
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atomic_cas!,
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atomic_xchg!,
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atomic_add!, atomic_sub!,
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atomic_and!, atomic_nand!, atomic_or!, atomic_xor!,
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atomic_max!, atomic_min!,
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atomic_fence
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# Disable 128-bit types on 32-bit Intel sytems due to LLVM problems;
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# see <https://github.com/JuliaLang/julia/issues/14818> (fixed on LLVM 3.9)
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# 128-bit atomics do not exist on AArch32.
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if (VersionNumber(Base.libllvm_version) < v"3.9-" && ARCH === :i686) ||
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startswith(string(ARCH), "arm")
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const inttypes = (Int8, Int16, Int32, Int64,
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UInt8, UInt16, UInt32, UInt64)
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else
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const inttypes = (Int8, Int16, Int32, Int64, Int128,
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UInt8, UInt16, UInt32, UInt64, UInt128)
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end
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const floattypes = (Float16, Float32, Float64)
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# TODO: Support Bool, Ptr
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const atomictypes = (inttypes..., floattypes...)
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const IntTypes = Union{inttypes...}
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const FloatTypes = Union{floattypes...}
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const AtomicTypes = Union{atomictypes...}
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"""
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Threads.Atomic{T}
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Holds a reference to an object of type `T`, ensuring that it is only
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accessed atomically, i.e. in a thread-safe manner.
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Only certain "simple" types can be used atomically, namely the
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primitive integer and float-point types. These are `Int8`...`Int128`,
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`UInt8`...`UInt128`, and `Float16`...`Float64`.
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New atomic objects can be created from a non-atomic values; if none is
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specified, the atomic object is initialized with zero.
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Atomic objects can be accessed using the `[]` notation:
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```jldoctest
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julia> x = Threads.Atomic{Int}(3)
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Base.Threads.Atomic{Int64}(3)
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julia> x[] = 1
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1
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julia> x[]
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1
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```
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Atomic operations use an `atomic_` prefix, such as `atomic_add!`,
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`atomic_xchg!`, etc.
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"""
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mutable struct Atomic{T<:AtomicTypes}
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value::T
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Atomic{T}() where {T<:AtomicTypes} = new(zero(T))
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Atomic{T}(value) where {T<:AtomicTypes} = new(value)
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end
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Atomic() = Atomic{Int}()
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"""
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Threads.atomic_cas!{T}(x::Atomic{T}, cmp::T, newval::T)
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Atomically compare-and-set `x`
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Atomically compares the value in `x` with `cmp`. If equal, write
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`newval` to `x`. Otherwise, leaves `x` unmodified. Returns the old
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value in `x`. By comparing the returned value to `cmp` (via `===`) one
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knows whether `x` was modified and now holds the new value `newval`.
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For further details, see LLVM's `cmpxchg` instruction.
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This function can be used to implement transactional semantics. Before
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the transaction, one records the value in `x`. After the transaction,
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the new value is stored only if `x` has not been modified in the mean
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time.
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```jldoctest
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julia> x = Threads.Atomic{Int}(3)
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Base.Threads.Atomic{Int64}(3)
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julia> Threads.atomic_cas!(x, 4, 2);
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julia> x
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Base.Threads.Atomic{Int64}(3)
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julia> Threads.atomic_cas!(x, 3, 2);
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julia> x
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Base.Threads.Atomic{Int64}(2)
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```
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"""
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function atomic_cas! end
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"""
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Threads.atomic_xchg!{T}(x::Atomic{T}, newval::T)
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Atomically exchange the value in `x`
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Atomically exchanges the value in `x` with `newval`. Returns the **old**
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value.
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For further details, see LLVM's `atomicrmw xchg` instruction.
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```jldoctest
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julia> x = Threads.Atomic{Int}(3)
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Base.Threads.Atomic{Int64}(3)
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julia> Threads.atomic_xchg!(x, 2)
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3
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julia> x[]
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2
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```
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"""
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function atomic_xchg! end
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"""
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Threads.atomic_add!{T}(x::Atomic{T}, val::T)
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Atomically add `val` to `x`
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Performs `x[] += val` atomically. Returns the **old** value.
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For further details, see LLVM's `atomicrmw add` instruction.
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```jldoctest
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julia> x = Threads.Atomic{Int}(3)
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Base.Threads.Atomic{Int64}(3)
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julia> Threads.atomic_add!(x, 2)
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3
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julia> x[]
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5
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```
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"""
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function atomic_add! end
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"""
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Threads.atomic_sub!{T}(x::Atomic{T}, val::T)
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Atomically subtract `val` from `x`
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Performs `x[] -= val` atomically. Returns the **old** value.
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For further details, see LLVM's `atomicrmw sub` instruction.
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```jldoctest
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julia> x = Threads.Atomic{Int}(3)
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Base.Threads.Atomic{Int64}(3)
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julia> Threads.atomic_sub!(x, 2)
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3
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julia> x[]
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1
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```
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"""
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function atomic_sub! end
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"""
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Threads.atomic_and!{T}(x::Atomic{T}, val::T)
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Atomically bitwise-and `x` with `val`
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Performs `x[] &= val` atomically. Returns the **old** value.
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For further details, see LLVM's `atomicrmw and` instruction.
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```jldoctest
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julia> x = Threads.Atomic{Int}(3)
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Base.Threads.Atomic{Int64}(3)
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julia> Threads.atomic_and!(x, 2)
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3
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julia> x[]
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2
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```
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"""
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function atomic_and! end
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"""
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Threads.atomic_nand!{T}(x::Atomic{T}, val::T)
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Atomically bitwise-nand (not-and) `x` with `val`
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Performs `x[] = ~(x[] & val)` atomically. Returns the **old** value.
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For further details, see LLVM's `atomicrmw nand` instruction.
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```jldoctest
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julia> x = Threads.Atomic{Int}(3)
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Base.Threads.Atomic{Int64}(3)
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julia> Threads.atomic_nand!(x, 2)
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3
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julia> x[]
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-3
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```
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"""
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function atomic_nand! end
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"""
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Threads.atomic_or!{T}(x::Atomic{T}, val::T)
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Atomically bitwise-or `x` with `val`
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Performs `x[] |= val` atomically. Returns the **old** value.
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For further details, see LLVM's `atomicrmw or` instruction.
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```jldoctest
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julia> x = Threads.Atomic{Int}(5)
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Base.Threads.Atomic{Int64}(5)
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julia> Threads.atomic_or!(x, 7)
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5
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julia> x[]
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7
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```
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"""
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function atomic_or! end
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"""
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Threads.atomic_xor!{T}(x::Atomic{T}, val::T)
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Atomically bitwise-xor (exclusive-or) `x` with `val`
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Performs `x[] \$= val` atomically. Returns the **old** value.
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For further details, see LLVM's `atomicrmw xor` instruction.
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```jldoctest
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julia> x = Threads.Atomic{Int}(5)
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Base.Threads.Atomic{Int64}(5)
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julia> Threads.atomic_xor!(x, 7)
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5
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julia> x[]
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2
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```
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"""
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function atomic_xor! end
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"""
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Threads.atomic_max!{T}(x::Atomic{T}, val::T)
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Atomically store the maximum of `x` and `val` in `x`
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Performs `x[] = max(x[], val)` atomically. Returns the **old** value.
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For further details, see LLVM's `atomicrmw max` instruction.
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```jldoctest
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julia> x = Threads.Atomic{Int}(5)
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Base.Threads.Atomic{Int64}(5)
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julia> Threads.atomic_max!(x, 7)
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5
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julia> x[]
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7
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```
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"""
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function atomic_max! end
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"""
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Threads.atomic_min!{T}(x::Atomic{T}, val::T)
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Atomically store the minimum of `x` and `val` in `x`
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Performs `x[] = min(x[], val)` atomically. Returns the **old** value.
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For further details, see LLVM's `atomicrmw min` instruction.
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```jldoctest
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julia> x = Threads.Atomic{Int}(7)
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Base.Threads.Atomic{Int64}(7)
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julia> Threads.atomic_min!(x, 5)
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7
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julia> x[]
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5
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```
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"""
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function atomic_min! end
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unsafe_convert(::Type{Ptr{T}}, x::Atomic{T}) where {T} = convert(Ptr{T}, pointer_from_objref(x))
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setindex!(x::Atomic{T}, v) where {T} = setindex!(x, convert(T, v))
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const llvmtypes = Dict(
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Bool => "i1",
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Int8 => "i8", UInt8 => "i8",
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Int16 => "i16", UInt16 => "i16",
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Int32 => "i32", UInt32 => "i32",
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Int64 => "i64", UInt64 => "i64",
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Int128 => "i128", UInt128 => "i128",
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Float16 => "i16", # half
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Float32 => "float",
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Float64 => "double",
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)
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inttype(::Type{T}) where {T<:Integer} = T
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inttype(::Type{Float16}) = Int16
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inttype(::Type{Float32}) = Int32
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inttype(::Type{Float64}) = Int64
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alignment(::Type{T}) where {T} = ccall(:jl_alignment, Cint, (Csize_t,), sizeof(T))
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# All atomic operations have acquire and/or release semantics, depending on
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# whether the load or store values. Most of the time, this is what one wants
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# anyway, and it's only moderately expensive on most hardware.
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for typ in atomictypes
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lt = llvmtypes[typ]
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ilt = llvmtypes[inttype(typ)]
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rt = VersionNumber(Base.libllvm_version) >= v"3.6" ? "$lt, $lt*" : "$lt*"
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irt = VersionNumber(Base.libllvm_version) >= v"3.6" ? "$ilt, $ilt*" : "$ilt*"
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if VersionNumber(Base.libllvm_version) >= v"3.8"
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@eval getindex(x::Atomic{$typ}) =
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llvmcall($"""
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%rv = load atomic $rt %0 acquire, align $(alignment(typ))
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ret $lt %rv
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""", $typ, Tuple{Ptr{$typ}}, unsafe_convert(Ptr{$typ}, x))
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@eval setindex!(x::Atomic{$typ}, v::$typ) =
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llvmcall($"""
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store atomic $lt %1, $lt* %0 release, align $(alignment(typ))
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ret void
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""", Void, Tuple{Ptr{$typ},$typ}, unsafe_convert(Ptr{$typ}, x), v)
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else
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if typ <: Integer
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@eval getindex(x::Atomic{$typ}) =
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llvmcall($"""
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%rv = load atomic $rt %0 acquire, align $(alignment(typ))
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ret $lt %rv
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""", $typ, Tuple{Ptr{$typ}}, unsafe_convert(Ptr{$typ}, x))
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@eval setindex!(x::Atomic{$typ}, v::$typ) =
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llvmcall($"""
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store atomic $lt %1, $lt* %0 release, align $(alignment(typ))
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ret void
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""", Void, Tuple{Ptr{$typ},$typ}, unsafe_convert(Ptr{$typ}, x), v)
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else
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@eval getindex(x::Atomic{$typ}) =
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llvmcall($"""
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%iptr = bitcast $lt* %0 to $ilt*
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%irv = load atomic $irt %iptr acquire, align $(alignment(typ))
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%rv = bitcast $ilt %irv to $lt
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ret $lt %rv
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""", $typ, Tuple{Ptr{$typ}}, unsafe_convert(Ptr{$typ}, x))
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@eval setindex!(x::Atomic{$typ}, v::$typ) =
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llvmcall($"""
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%iptr = bitcast $lt* %0 to $ilt*
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%ival = bitcast $lt %1 to $ilt
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store atomic $ilt %ival, $ilt* %iptr release, align $(alignment(typ))
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ret void
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""", Void, Tuple{Ptr{$typ},$typ}, unsafe_convert(Ptr{$typ}, x), v)
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end
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end
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# Note: atomic_cas! succeeded (i.e. it stored "new") if and only if the result is "cmp"
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if VersionNumber(Base.libllvm_version) >= v"3.5"
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if typ <: Integer
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@eval atomic_cas!(x::Atomic{$typ}, cmp::$typ, new::$typ) =
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llvmcall($"""
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%rs = cmpxchg $lt* %0, $lt %1, $lt %2 acq_rel acquire
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%rv = extractvalue { $lt, i1 } %rs, 0
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ret $lt %rv
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""", $typ, Tuple{Ptr{$typ},$typ,$typ},
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unsafe_convert(Ptr{$typ}, x), cmp, new)
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else
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@eval atomic_cas!(x::Atomic{$typ}, cmp::$typ, new::$typ) =
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llvmcall($"""
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%iptr = bitcast $lt* %0 to $ilt*
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%icmp = bitcast $lt %1 to $ilt
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%inew = bitcast $lt %2 to $ilt
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%irs = cmpxchg $ilt* %iptr, $ilt %icmp, $ilt %inew acq_rel acquire
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%irv = extractvalue { $ilt, i1 } %irs, 0
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%rv = bitcast $ilt %irv to $lt
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ret $lt %rv
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""", $typ, Tuple{Ptr{$typ},$typ,$typ},
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unsafe_convert(Ptr{$typ}, x), cmp, new)
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end
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else
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if typ <: Integer
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@eval atomic_cas!(x::Atomic{$typ}, cmp::$typ, new::$typ) =
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llvmcall($"""
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%rv = cmpxchg $lt* %0, $lt %1, $lt %2 acq_rel
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ret $lt %rv
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""", $typ, Tuple{Ptr{$typ},$typ,$typ},
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unsafe_convert(Ptr{$typ}, x), cmp, new)
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else
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@eval atomic_cas!(x::Atomic{$typ}, cmp::$typ, new::$typ) =
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llvmcall($"""
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%iptr = bitcast $lt* %0 to $ilt*
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%icmp = bitcast $lt %1 to $ilt
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%inew = bitcast $lt %2 to $ilt
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%irv = cmpxchg $ilt* %iptr, $ilt %icmp, $ilt %inew acq_rel
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%rv = bitcast $ilt %irv to $lt
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ret $lt %rv
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""", $typ, Tuple{Ptr{$typ},$typ,$typ},
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unsafe_convert(Ptr{$typ}, x), cmp, new)
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end
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end
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for rmwop in [:xchg, :add, :sub, :and, :nand, :or, :xor, :max, :min]
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rmw = string(rmwop)
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fn = Symbol("atomic_", rmw, "!")
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if (rmw == "max" || rmw == "min") && typ <: Unsigned
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# LLVM distinguishes signedness in the operation, not the integer type.
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rmw = "u" * rmw
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end
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if typ <: Integer
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@eval $fn(x::Atomic{$typ}, v::$typ) =
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llvmcall($"""
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%rv = atomicrmw $rmw $lt* %0, $lt %1 acq_rel
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ret $lt %rv
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""", $typ, Tuple{Ptr{$typ}, $typ}, unsafe_convert(Ptr{$typ}, x), v)
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else
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rmwop == :xchg || continue
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@eval $fn(x::Atomic{$typ}, v::$typ) =
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llvmcall($"""
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%iptr = bitcast $lt* %0 to $ilt*
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%ival = bitcast $lt %1 to $ilt
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%irv = atomicrmw $rmw $ilt* %iptr, $ilt %ival acq_rel
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%rv = bitcast $ilt %irv to $lt
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ret $lt %rv
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""", $typ, Tuple{Ptr{$typ}, $typ}, unsafe_convert(Ptr{$typ}, x), v)
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end
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end
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end
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# Provide atomic floating-point operations via atomic_cas!
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const opnames = Dict{Symbol, Symbol}(:+ => :add, :- => :sub)
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for op in [:+, :-, :max, :min]
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opname = get(opnames, op, op)
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@eval function $(Symbol("atomic_", opname, "!"))(var::Atomic{T}, val::T) where T<:FloatTypes
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IT = inttype(T)
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old = var[]
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while true
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new = $op(old, val)
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cmp = old
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old = atomic_cas!(var, cmp, new)
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reinterpret(IT, old) == reinterpret(IT, cmp) && return new
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# Temporary solution before we have gc transition support in codegen.
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ccall(:jl_gc_safepoint, Void, ())
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end
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end
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end
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"""
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Threads.atomic_fence()
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Insert a sequential-consistency memory fence
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Inserts a memory fence with sequentially-consistent ordering
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semantics. There are algorithms where this is needed, i.e. where an
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acquire/release ordering is insufficient.
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This is likely a very expensive operation. Given that all other atomic
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operations in Julia already have acquire/release semantics, explicit
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fences should not be necessary in most cases.
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For further details, see LLVM's `fence` instruction.
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"""
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atomic_fence() = llvmcall("""
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fence seq_cst
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ret void
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""", Void, Tuple{})
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