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Fix a concurrency bug in iterate(::Dict)#44534

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DilumAluthge merged 4 commits intoJuliaLang:masterfrom
tkf:dict-iterate
Mar 12, 2022
Merged

Fix a concurrency bug in iterate(::Dict)#44534
DilumAluthge merged 4 commits intoJuliaLang:masterfrom
tkf:dict-iterate

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@tkf tkf commented Mar 9, 2022

fix #35835

This patch simply avoids mutating the Dict struct in iterate.

An alternative (probably correct) fix is

diff --git a/base/dict.jl b/base/dict.jl
index 12ff26fbeb..c98ae28947 100644
--- a/base/dict.jl
+++ b/base/dict.jl
@@ -696,7 +696,7 @@ end
 function skip_deleted_floor!(h::Dict)
     idx = skip_deleted(h, h.idxfloor)
     if idx != 0
-        h.idxfloor = idx
+        @atomic :monotonic h.idxfloor = idx
     end
     idx
 end

but I'm posting a simpler approach since I think it makes keeping Dict implementation correct hard and drastically decreases the number of maintainers who can reason about Dict code.

@tkf tkf requested a review from vtjnash March 9, 2022 05:50
@tkf tkf added collections Data structures holding multiple items, e.g. sets multithreading Base.Threads and related functionality labels Mar 9, 2022
vtjnash
vtjnash approved these changes Mar 10, 2022
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Seems like the main purpose is to make pop! work in O(1) time, so we do not need it here.

@tkf tkf added the merge me PR is reviewed. Merge when all tests are passing label Mar 10, 2022
@DilumAluthge DilumAluthge merged commit 6be86a3 into JuliaLang:master Mar 12, 2022
@tkf tkf deleted the dict-iterate branch March 12, 2022 01:11
@giordano giordano removed the merge me PR is reviewed. Merge when all tests are passing label Mar 12, 2022
@IanButterworth IanButterworth added backport 1.6 Change should be backported to release-1.6 backport 1.7 backport 1.8 Change should be backported to release-1.8 labels Apr 28, 2022
This was referenced May 16, 2022
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KristofferC pushed a commit that referenced this pull request May 16, 2022
@tkf
Fix a concurrency bug in iterate(::Dict) (#44534)
b3dde45 
(cherry picked from commit 6be86a3)
KristofferC pushed a commit that referenced this pull request May 23, 2022
@tkf
Fix a concurrency bug in iterate(::Dict) (#44534)
4a4b3fb 
(cherry picked from commit 6be86a3)
KristofferC pushed a commit that referenced this pull request May 23, 2022
@tkf
Fix a concurrency bug in iterate(::Dict) (#44534)
06d71b8 
(cherry picked from commit 6be86a3)
@KristofferC KristofferC removed the backport 1.8 Change should be backported to release-1.8 label May 28, 2022
@KristofferC KristofferC removed the backport 1.6 Change should be backported to release-1.6 label Jul 6, 2022
KristofferC pushed a commit that referenced this pull request Dec 21, 2022
@tkf
Fix a concurrency bug in iterate(::Dict) (#44534)
be53763 
(cherry picked from commit 6be86a3)
staticfloat pushed a commit that referenced this pull request Dec 23, 2022
@tkf @staticfloat
Fix a concurrency bug in iterate(::Dict) (#44534)
56d307f 
(cherry picked from commit 6be86a3)
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@JeffBezanson JeffBezanson JeffBezanson approved these changes

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Data-race in iterate(::Dict)?

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@tkf @vtjnash @JeffBezanson @giordano @KristofferC @IanButterworth @DilumAluthge