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fixclose error due to race ind_closeall#248
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The below code that adds some code to regulate GC behavior can recreate the situation. julia>using Distributedjulia>addprocs(4);julia>@everywherebeginusing Distributed, DistributedArraysendjulia> A=rand(1:100, (100,100));julia> DA=distribute(A);julia> GC.enable(false)truejulia> DA=nothingjulia>function DistributedArrays.d_from_weakref_or_d(id) d=get(DistributedArrays.registry, id,nothing) GC.enable(true) GC.gc()isa(d, WeakRef)&&return d.valuereturn dendjulia> DistributedArrays.d_closeall()ERROR: MethodError: no method matchingclose(::Nothing)Closest candidates are:close(::Union{Base.AsyncCondition, Timer}) @ Base asyncevent.jl:162close(::Union{FileWatching.FileMonitor, FileWatching.FolderMonitor, FileWatching.PollingFileWatcher}) @ FileWatching/data/Work/julia/binaries/julia-1.9.3/share/julia/stdlib/v1.9/FileWatching/src/FileWatching.jl:328close(::DArray) @ DistributedArrays~/.julia/dev/DistributedArrays/src/core.jl:34...Stacktrace: [1]d_closeall() @ DistributedArrays~/.julia/dev/DistributedArrays/src/core.jl:47 [2] top-level scope @ REPL[9]:1 |
It seems possible that `DistributedArrays.d_closeall()` may encounter a condition where it finds a darray id in the `registry`, but the corresponding weakref value is `nothing` because the referenced darray got garbage collected. It has been enountered many times in CI and elsewhere, but is hard to replicate normally. Adding a check for the weakref value, before actually invoking `close` on it, to fix it.
Can we be sure that the remote memory is properly freed if the reference has been garbage collected? |
Yes, I think so, because the finalizer invokes julia>using Distributedjulia>addprocs(4);julia>@everywherebeginusing Distributed, DistributedArraysfunctionprint_registry_entries()for kinkeys(DistributedArrays.registry) hasval=!(DistributedArrays.d_from_weakref_or_d(k)===nothing)println("key$k hasval$hasval")endendendjulia>@everywhereprint_registry_entries()julia> A=rand(1:100, (100,100));julia> DA=distribute(A);julia> GC.enable(false)truejulia> DA=nothingjulia>@everywhereprint_registry_entries()key (1,1) hasvaltrue From worker5:key (1,1) hasvaltrue From worker3:key (1,1) hasvaltrue From worker2:key (1,1) hasvaltrue From worker4:key (1,1) hasvaltruejulia>function DistributedArrays.d_from_weakref_or_d(id) d=get(DistributedArrays.registry, id,nothing) GC.enable(true) GC.gc()isa(d, WeakRef)&&return d.valuereturn dendjulia>@everywhereprint_registry_entries()key (1,1) hasvalfalse From worker2:key (1,1) hasvaltrue From worker3:key (1,1) hasvaltrue From worker5:key (1,1) hasvaltrue From worker4:key (1,1) hasvaltruejulia> DistributedArrays.d_closeall()julia>@everywhereprint_registry_entries() Would it be good to add this as a test? |
andreasnoack approved these changesOct 3, 2023
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I think it is fine as it is
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It seems possible that
DistributedArrays.d_closeall()may encounter a condition where it finds a darray id in theregistry, but the corresponding weakref value isnothingbecause the referenced darray got garbage collected. It has been enountered many times in CI and elsewhere, but is hard to replicate normally. Adding a check for the weakref value, before actually invokingcloseon it, to fix it.fixes#246