Backport deque memory fix (#898)

* Use `Base._unsetindex!` in `pop!` and `popfirst!` (#897)

* Bump codecov/codecov-action from 3 to 4

Bumps [codecov/codecov-action](https://github.com/codecov/codecov-action) from 3 to 4.
- [Release notes](https://github.com/codecov/codecov-action/releases)
- [Changelog](https://github.com/codecov/codecov-action/blob/main/CHANGELOG.md)
- [Commits](codecov/codecov-action@v3...v4)

---
updated-dependencies:
- dependency-name: codecov/codecov-action
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <support@github.com>

* Use `Base._unsetindex!` in `pop!` and `popfirst!` for Deque

So that popped elements are not rooted by the deque and can be
GCed when they drop out of caller scope.

* Test Deque for leaks

* Use `Base._unsetindex!` in `pop!` and `popfirst!` for CircularDeque

So that popped elements are not rooted by the deque and can be GCed
when they drop out of caller scope.

* Test CircularDeque for leaks

---------

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

* Bump version

* Make compatible with ancient Julia versions

* fixup! Make compatible with ancient Julia versions

* fixup! fixup! Make compatible with ancient Julia versions

---------

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: Kiran Pamnany <kpamnany@users.noreply.github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Project.toml

@@ -1,6 +1,6 @@
 name = "DataStructures"
 uuid = "864edb3b-99cc-5e75-8d2d-829cb0a9cfe8"
-version = "0.18.16"
+version = "0.18.17"
 
 [deps]
 Compat = "34da2185-b29b-5c13-b0c7-acf172513d20"

src/DataStructures.jl

@@ -112,4 +112,10 @@ module DataStructures
     include("splay_tree.jl")
 
     include("deprecations.jl")
-end
+
+    @static if VERSION <= v"1.3"
+        _unsetindex!(a, i) = a
+    else
+        _unsetindex! = Base._unsetindex!
+    end
+end

src/circ_deque.jl

@@ -63,6 +63,7 @@ end
 
 @inline Base.@propagate_inbounds function Base.pop!(D::CircularDeque)
     v = last(D)
+    _unsetindex!(D.buffer, D.last) # see issue/884
     D.n -= 1
     tmp = D.last - 1
     D.last = ifelse(tmp < 1, D.capacity, tmp)
@@ -90,6 +91,7 @@ Remove the element at the front.
 """
 @inline Base.@propagate_inbounds function Base.popfirst!(D::CircularDeque)
     v = first(D)
+    _unsetindex!(D.buffer, D.first) # see issue/884
     D.n -= 1
     tmp = D.first + 1
     D.first = ifelse(tmp > D.capacity, 1, tmp)

src/deque.jl

@@ -276,6 +276,7 @@ function Base.pop!(q::Deque{T}) where T
     @assert rear.back >= rear.front
 
     @inbounds x = rear.data[rear.back]
+    _unsetindex!(rear.data, rear.back) # see issue/884
     rear.back -= 1
     if rear.back < rear.front
         if q.nblocks > 1
@@ -301,6 +302,7 @@ function Base.popfirst!(q::Deque{T}) where T
     @assert head.back >= head.front
 
     @inbounds x = head.data[head.front]
+    _unsetindex!(head.data, head.front) # see issue/884
     head.front += 1
     if head.back < head.front
         if q.nblocks > 1

test/test_circ_deque.jl

@@ -81,6 +81,29 @@
         for i in 1:5 push!(D, i) end
         @test collect([i for i in D]) == collect(1:5)
     end
+
+    VERSION >= v"1.3" && @testset "pop! and popfirst! do not leak" begin
+        D = CircularDeque{String}(5)
+
+        @testset "pop! doesn't leak" begin
+            push!(D,"foo")
+            push!(D,"bar")
+            ss2 = Base.summarysize(D)
+            pop!(D)
+            GC.gc(true)
+            ss1 = Base.summarysize(D)
+            @test ss1 < ss2
+        end
+        @testset "popfirst! doesn't leak" begin
+            push!(D,"baz")
+            push!(D,"bug")
+            ss2 = Base.summarysize(D)
+            popfirst!(D)
+            GC.gc(true)
+            ss1 = Base.summarysize(D)
+            @test ss1 < ss2
+        end
+    end
 end
 
 nothing

test/test_deque.jl

@@ -197,4 +197,28 @@
         @test typeof(empty!(q)) === typeof(Deque{Int}())
         @test isempty(q)
     end
+
+    VERSION >= v"1.3" && @testset "pop! and popfirst! don't leak" begin
+        q = Deque{String}(5)
+        GC.gc(true)
+
+        @testset "pop! doesn't leak" begin
+            push!(q,"foo")
+            push!(q,"bar")
+            ss2 = Base.summarysize(q.head)
+            pop!(q)
+            GC.gc(true)
+            ss1 = Base.summarysize(q.head)
+            @test ss1 < ss2
+        end
+        @testset "popfirst! doesn't leak" begin
+            push!(q,"baz")
+            push!(q,"bug")
+            ss2 = Base.summarysize(q.head)
+            popfirst!(q)
+            GC.gc(true)
+            ss1 = Base.summarysize(q.head)
+            @test ss1 < ss2
+        end
+    end
 end # @testset Deque