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Introduce sizehint!(s, n; shrink = true) to controll shrinkage #51929

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merged 11 commits into from
Nov 8, 2023
Merged

Introduce sizehint!(s, n; shrink = true) to controll shrinkage #51929

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2634a30
Introduce sizehint!(s, n; shrink = true) to controll shrinkage
petvana Oct 29, 2023
d7eceb4
Add shrinkage control for Vector
petvana Oct 29, 2023
0735eea
Add shrinkage control for Set
petvana Oct 29, 2023
271f999
Add tests for Set and Vector
petvana Oct 31, 2023
620cd2b
lock WeakKeyDict
petvana Nov 1, 2023
c0c055b
Make shrink Bool in base/array.jl
petvana Nov 3, 2023
088b152
Force shrink to be Bool
petvana Nov 3, 2023
b1c8338
Merge branch 'pv/dict-controll-shrinkage-v3' of github.com:petvana/ju…
petvana Nov 3, 2023
655a5bc
Compat + news
petvana Nov 3, 2023
42ff9ec
Typo
petvana Nov 3, 2023
35b2950
Merge branch 'master' into pv/dict-controll-shrinkage-v3
petvana Nov 4, 2023
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1 change: 1 addition & 0 deletions NEWS.md
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Expand Up @@ -56,6 +56,7 @@ New library features
--------------------
* `replace(string, pattern...)` now supports an optional `IO` argument to
write the output to a stream rather than returning a string ([#48625]).
* `sizehint!(s, n)` now supports an optional `shrink` argument to disable shrinking ([#51929]).

Standard library changes
------------------------
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3 changes: 1 addition & 2 deletions base/abstractdict.jl
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Expand Up @@ -220,8 +220,7 @@ Dict{Int64, Int64} with 3 entries:
function merge!(d::AbstractDict, others::AbstractDict...)
for other in others
if haslength(d) && haslength(other)
# TODO - do not shrink
sizehint!(d, length(d) + length(other))
sizehint!(d, length(d) + length(other); shrink = false)
end
for (k,v) in other
d[k] = v
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2 changes: 1 addition & 1 deletion base/abstractset.jl
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Expand Up @@ -101,7 +101,7 @@ max_values(::Type{Bool}) = 2
max_values(::Type{Nothing}) = 1

function union!(s::AbstractSet{T}, itr) where T
haslength(itr) && _sizehint!(s, length(s) + Int(length(itr))::Int; shrink = false)
haslength(itr) && sizehint!(s, length(s) + Int(length(itr))::Int; shrink = false)
for x in itr
push!(s, x)
length(s) == max_values(T) && break
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13 changes: 9 additions & 4 deletions base/array.jl
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Expand Up @@ -1441,7 +1441,7 @@ function resize!(a::Vector, nl::Integer)
end

"""
sizehint!(s, n) -> s
sizehint!(s, n; shrink::Bool = true) -> s

Suggest that collection `s` reserve capacity for at least `n` elements. That is, if
you expect that you're going to have to push a lot of values onto `s`, you can avoid
Expand All @@ -1462,10 +1462,15 @@ For types that support `sizehint!`,
`Base`.

3. `empty!` is nearly costless (and O(1)) for types that support this kind of preallocation.

4. `shrink` controls if the collection can be shrunk.
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Reading this, I don't understand what the argument does. Would you mind adding a more detailed explanation? Also it would seem more appropriate to mention the argument above, outside of the "# Notes on the performance model", as I wouldn't expect to have to read a performance section to find out the meaning of an argument.

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Thanks, this seems like a fair point. The new optional argument enables us to suggest not to shrink the already reserved capacity when suggesting new size by setting shrink = false. This is helpful for algorithms like merging two collection where you want to pre-allocate memory, but there is not reason to change (shrink) size if all the data fits. I'm not a native speaker, would you be able to propose a more fitting description?

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I've not a native speaker either, but see #52226. I hope I got it right.


!!! compat "Julia 1.11"
The `shrink` argument was added in Julia 1.11.
"""
function sizehint! end

function sizehint!(a::Vector, sz::Integer)
function sizehint!(a::Vector, sz::Integer; shrink::Bool = true)
len = length(a)
ref = a.ref
mem = ref.mem
Expand All @@ -1474,7 +1479,7 @@ function sizehint!(a::Vector, sz::Integer)
sz = max(Int(sz), offset + len - 1)
if sz <= memlen
# if we don't save at least 1/8th memlen then its not worth it to shrink
if memlen - sz <= div(memlen, 8)
if !shrink || memlen - sz <= div(memlen, 8)
return a
end
newmem = array_new_memory(mem, sz)
Expand All @@ -1494,7 +1499,7 @@ function sizehint!(a::Vector, sz::Integer)
end

# Fall-back implementation for non-shrinkable collections
_sizehint!(a, sz; shrink) = sizehint!(a, sz)
sizehint!(a, sz; shrink::Bool) = sizehint!(a, sz)
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"""
pop!(collection) -> item
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6 changes: 2 additions & 4 deletions base/dict.jl
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Expand Up @@ -228,7 +228,7 @@ end
return h
end

function _sizehint!(d::Dict{T}, newsz; shrink = true) where T
function sizehint!(d::Dict{T}, newsz; shrink::Bool = true) where T
oldsz = length(d.slots)
# limit new element count to max_values of the key type
newsz = min(max(newsz, length(d)), max_values(T)::Int)
Expand All @@ -237,8 +237,6 @@ function _sizehint!(d::Dict{T}, newsz; shrink = true) where T
return (shrink ? newsz == oldsz : newsz <= oldsz) ? d : rehash!(d, newsz)
end

sizehint!(d::Dict{T}, newsz) where T = _sizehint!(d, newsz)

"""
empty!(collection) -> collection

Expand Down Expand Up @@ -777,7 +775,7 @@ function map!(f, iter::ValueIterator{<:Dict})
end

function mergewith!(combine, d1::Dict{K, V}, d2::AbstractDict) where {K, V}
haslength(d2) && _sizehint!(d1, length(d1) + length(d2), shrink = false)
haslength(d2) && sizehint!(d1, length(d1) + length(d2), shrink = false)
for (k, v) in d2
i, sh = ht_keyindex2_shorthash!(d1, k)
if i > 0
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2 changes: 1 addition & 1 deletion base/set.jl
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Expand Up @@ -117,7 +117,7 @@ copymutable(s::Set{T}) where {T} = Set{T}(s)
# Set is the default mutable fall-back
copymutable(s::AbstractSet{T}) where {T} = Set{T}(s)

sizehint!(s::Set, newsz) = (sizehint!(s.dict, newsz); s)
sizehint!(s::Set, newsz; shrink::Bool = true) = (sizehint!(s.dict, newsz, shrink = shrink); s)
empty!(s::Set) = (empty!(s.dict); s)
rehash!(s::Set) = (rehash!(s.dict); s)

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2 changes: 1 addition & 1 deletion base/weakkeydict.jl
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Expand Up @@ -80,7 +80,7 @@ function _cleanup_locked(h::WeakKeyDict)
return h
end

sizehint!(d::WeakKeyDict, newsz) = sizehint!(d.ht, newsz)
sizehint!(d::WeakKeyDict, newsz; shrink::Bool = true) = @lock d sizehint!(d.ht, newsz; shrink = shrink)
empty(d::WeakKeyDict, ::Type{K}, ::Type{V}) where {K, V} = WeakKeyDict{K, V}()

IteratorSize(::Type{<:WeakKeyDict}) = SizeUnknown()
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4 changes: 2 additions & 2 deletions test/dict.jl
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Expand Up @@ -1492,9 +1492,9 @@ end
sizehint!(d, 10)
@test length(d.slots) < 100
sizehint!(d, 1000)
Base._sizehint!(d, 1; shrink = false)
sizehint!(d, 1; shrink = false)
@test length(d.slots) >= 1000
Base._sizehint!(d, 1; shrink = true)
sizehint!(d, 1; shrink = true)
@test length(d.slots) < 1000
end

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15 changes: 15 additions & 0 deletions test/sets.jl
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Expand Up @@ -164,6 +164,19 @@ end
sizehint!(s2, 10)
@test s2 == GenericSet(s)
end

@testset "shrinking" begin # Similar test as for the underlying Dict
d = Set(i for i = 1:1000)
filter!(x -> x < 10, d)
sizehint!(d, 10)
@test length(d.dict.slots) < 100
sizehint!(d, 1000)
sizehint!(d, 1; shrink = false)
@test length(d.dict.slots) >= 1000
sizehint!(d, 1; shrink = true)
@test length(d.dict.slots) < 1000
end

@testset "rehash!" begin
# Use a pointer type to have defined behavior for uninitialized
# array element
Expand Down Expand Up @@ -966,4 +979,6 @@ end
end
set = TestSet{Any}()
@test sizehint!(set, 1) === set
@test sizehint!(set, 1; shrink = true) === set
@test sizehint!(set, 1; shrink = false) === set
end
61 changes: 18 additions & 43 deletions test/smallarrayshrink.jl
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@@ -1,45 +1,20 @@
@testset "shrink small array" begin
x = [1, 2, 3, 4]
@test x[1] == 1
@test x[2] == 2
@test x[3] == 3
@test x[4] == 4
@test ccall(:jl_array_size, Int, (Any, UInt), x, 0) == 4
@test ccall(:jl_array_size, Int, (Any, UInt), x, 1) == 4
sizehint!(x, 10000)
@test x[1] == 1
@test x[2] == 2
@test x[3] == 3
@test x[4] == 4
@test ccall(:jl_array_size, Int, (Any, UInt), x, 0) == 4
@test ccall(:jl_array_size, Int, (Any, UInt), x, 1) == 10000
sizehint!(x, 4)
@test x[1] == 1
@test x[2] == 2
@test x[3] == 3
@test x[4] == 4
@test ccall(:jl_array_size, Int, (Any, UInt), x, 0) == 4
@test ccall(:jl_array_size, Int, (Any, UInt), x, 1) == 4

x = [1, 2, 3, 4]
@test x[1] == 1
@test x[2] == 2
@test x[3] == 3
@test x[4] == 4
@test ccall(:jl_array_size, Int, (Any, UInt), x, 0) == 4
@test ccall(:jl_array_size, Int, (Any, UInt), x, 1) == 4
sizehint!(x, 1000000)
@test x[1] == 1
@test x[2] == 2
@test x[3] == 3
@test x[4] == 4
@test ccall(:jl_array_size, Int, (Any, UInt), x, 0) == 4
@test ccall(:jl_array_size, Int, (Any, UInt), x, 1) == 1000000
sizehint!(x, 4)
@test x[1] == 1
@test x[2] == 2
@test x[3] == 3
@test x[4] == 4
@test ccall(:jl_array_size, Int, (Any, UInt), x, 0) == 4
@test ccall(:jl_array_size, Int, (Any, UInt), x, 1) == 4
function check_array(x, size, capacity)
@test x[1] == 1
@test x[2] == 2
@test x[3] == 3
@test x[4] == 4
@test ccall(:jl_array_size, Int, (Any, UInt), x, 0) == size
@test ccall(:jl_array_size, Int, (Any, UInt), x, 1) == capacity
end
for hint_size = [10000, 1000000]
x = [1, 2, 3, 4]
check_array(x, 4, 4)
sizehint!(x, hint_size)
check_array(x, 4, hint_size)
sizehint!(x, 4; shrink = false)
check_array(x, 4, hint_size)
sizehint!(x, 4)
check_array(x, 4, 4)
end
end