Fix missing write barrier on Generator State #826
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Found by wbcheck
WBCHECK ERROR: Missed write barrier detected!
Parent object: 0x7b7b8487c450 (wb_protected: true)
rb_obj_info_dump: 0x00007b7b8487c450 JSON/Generator/State/JSON::Ext::Generator::State JSON/Generator/State
Reference counts - snapshot: 1, writebarrier: 0, current: 6, missed: 5
Missing reference to: 0x7b7b82f35a10
rb_obj_info_dump: 0x00007b7b82f35a10 T_STRING/String len: 1, capa: 15 "1"
Missing reference to: 0x7b7b82f35e90
rb_obj_info_dump: 0x00007b7b82f35e90 T_STRING/String len: 1, capa: 15 "2"
Missing reference to: 0x7b7b83629e50
rb_obj_info_dump: 0x00007b7b83629e50 T_STRING/String len: 1, capa: 15 "3"
Missing reference to: 0x7b7b83b62190
rb_obj_info_dump: 0x00007b7b83b62190 T_STRING/String len: 1, capa: 15 "4"
Missing reference to: 0x7b7b83629490
rb_obj_info_dump: 0x00007b7b83629490 T_STRING/String len: 1, capa: 15 "5"
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Good catch. I don't think this can realistically cause a bug, but I'm all for silencing what wbcheck finds. |
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I agree it's unlikely in practice for the bug here to be hit, but I'm trying to convince both myself and others that nearly everything wbcheck finds is a "real" issue: require "json"
state1 = JSON.state.new
3.times { GC.start }
state1.merge(
indent: 1.to_s,
space: 2.to_s,
space_before: 3.to_s,
object_nl: 4.to_s,
array_nl: 5.to_s
)
GC.start(full_mark: false)
state1.generate({foo: 123}) |
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Yeah, when I say unlikely, is that the object wouldn't be old by that point (unless GC.stress etc). So defiitely real, but also definitely almost impossible to happen in real world code, hence likely why it was missed. This is more me stating that this doesn't warrant a bug fix release on its own. |
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Found by wbcheck. This should only be a problem when state is an object rather than stack allocated.