`ObjectFile` not thread-safe

[giordano]

In the effort of making BinaryBuilder's Auditor parallel I ran into race conditions during access to object handles:

nested task error: EOFError: read end of file
Stacktrace:
  [1] unsafe_read(s::IOStream, p::Ptr{UInt8}, nb::UInt64)
    @ Base ./iostream.jl:427
  [2] unsafe_read
    @ ./io.jl:724 [inlined]
  [3] unsafe_read(s::IOStream, p::Base.RefValue{ELFSection64{ELFHandle{IOStream}}}, n::Int64)
    @ Base ./io.jl:723
  [4] unsafe_unpack(io::IOStream, #unused#::Type{ELFSection64{ELFHandle{IOStream}}}, target::Base.RefValue{ELFSection64{ELFHandle{IOStream}}}, endianness::Symbol, #unused#::Type{StructIO.Default})
    @ StructIO /data/staticfloat/bb_azp/rootfs/agent_2/depot/packages/StructIO/c2JPj/src/StructIO.jl:158
  [5] unpack(io::IOStream, T::Type, endianness::Symbol)
    @ StructIO /data/staticfloat/bb_azp/rootfs/agent_2/depot/packages/StructIO/c2JPj/src/StructIO.jl:292
  [6] unpack(oh::ELFHandle{IOStream}, T::Type)
    @ ObjectFile /data/staticfloat/bb_azp/rootfs/agent_2/depot/packages/ObjectFile/GXCd7/src/Abstract/ObjectHandle.jl:183
  [7] getindex_ref(collection::ELFSections{ELFHandle{IOStream}}, offset::UInt64, stride::UInt16, T::Type, ref_type::Type{SectionRef}, idx::Int64)
    @ ObjectFile /data/staticfloat/bb_azp/rootfs/agent_2/depot/packages/ObjectFile/GXCd7/src/utils.jl:175
  [8] getindex(sections::ELFSections{ELFHandle{IOStream}}, idx::Int64)
    @ ObjectFile /data/staticfloat/bb_azp/rootfs/agent_2/depot/packages/ObjectFile/GXCd7/src/Abstract/Section.jl:60
  [9] iterate(sections::ELFSections{ELFHandle{IOStream}}, idx::Int64) (repeats 2 times)
    @ ObjectFile /data/staticfloat/bb_azp/rootfs/agent_2/depot/packages/ObjectFile/GXCd7/src/Abstract/Section.jl:54
 [10] iterate(::Base.Iterators.Filter{ObjectFile.var"#9#10"{Vector{String}}, ELFSections{ELFHandle{IOStream}}})
    @ Base.Iterators ./iterators.jl:445
 [11] iterate
    @ ./generator.jl:44 [inlined]
 [12] grow_to!
    @ ./array.jl:797 [inlined]
 [13] collect(itr::Base.Generator{Base.Iterators.Filter{ObjectFile.var"#9#10"{Vector{String}}, ELFSections{ELFHandle{IOStream}}}, typeof(identity)})
    @ Base ./array.jl:721
 [14] findall
    @ /data/staticfloat/bb_azp/rootfs/agent_2/depot/packages/ObjectFile/GXCd7/src/Abstract/Section.jl:85 [inlined]
 [15] findfirst
    @ /data/staticfloat/bb_azp/rootfs/agent_2/depot/packages/ObjectFile/GXCd7/src/Abstract/Section.jl:103 [inlined]
 [16] findfirst
    @ /data/staticfloat/bb_azp/rootfs/agent_2/depot/packages/ObjectFile/GXCd7/src/Abstract/Section.jl:94 [inlined]
 [17] RPath(oh::ELFHandle{IOStream})
    @ ObjectFile.ELF /data/staticfloat/bb_azp/rootfs/agent_2/depot/packages/ObjectFile/GXCd7/src/ELF/ELFDynamicLink.jl:103
 [18] _broadcast_getindex_evalf
    @ ./broadcast.jl:670 [inlined]
 [19] _broadcast_getindex
    @ ./broadcast.jl:643 [inlined]
 [20] _getindex
    @ ./broadcast.jl:667 [inlined]
 [21] _broadcast_getindex
    @ ./broadcast.jl:642 [inlined]
 [22] getindex
    @ ./broadcast.jl:597 [inlined]
 [23] copy
    @ ./broadcast.jl:899 [inlined]
 [24] materialize
    @ ./broadcast.jl:860 [inlined]
 [25] (::BinaryBuilder.Auditor.var"#10#11")(ohs::Vector{ELFHandle{IOStream}})
    @ BinaryBuilder.Auditor /data/staticfloat/bb_azp/rootfs/agent_2/_work/1/s/src/auditor/dynamic_linkage.jl:80
 [26] readmeta(f::BinaryBuilder.Auditor.var"#10#11", file::String)
    @ ObjectFile /data/staticfloat/bb_azp/rootfs/agent_2/depot/packages/ObjectFile/GXCd7/src/Abstract/ObjectHandle.jl:160
 [27] _canonical_rpaths
    @ /data/staticfloat/bb_azp/rootfs/agent_2/_work/1/s/src/auditor/dynamic_linkage.jl:79 [inlined]
 [28] update_linkage(prefix::Prefix, platform::Platform, path::String, old_libpath::SubString{String}, new_libpath::String; verbose::Bool, subdir::String)
    @ BinaryBuilder.Auditor /data/staticfloat/bb_azp/rootfs/agent_2/_work/1/s/src/auditor/dynamic_linkage.jl:469
 [29] macro expansion
    @ /data/staticfloat/bb_azp/rootfs/agent_2/_work/1/s/src/Auditor.jl:444 [inlined]
 [30] (::BinaryBuilder.Auditor.var"#127#128"{Platform, Bool, Bool, Bool, String, ELFHandle{IOStream}, Prefix, Vector{String}, Dict{SubString{String}, SubString{String}}, String, Base.Threads.Atomic{Bool}, SubString{String}})()
    @ BinaryBuilder.Auditor ./threadingconstructs.jl:178

My understanding is that reading the handle isn't thread-safe. I'm working around this in BB (I think), butit'd be nicer if object files handles were thread-safe by default (e.g. with a lock to automatically acquired when performing unsafe operations).

Edit: however the stacktrace points to this line in a serial function (called inside a threaded region) where however there's a single object handle for the file in question, so I'm not entirely sure where the race condition is coming from 🤔