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RFC: serialize pointer- and padding-free objects in one write #14678

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RFC: serialize pointer- and padding-free objects in one write #14678

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19 changes: 14 additions & 5 deletions base/serialize.jl
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Original file line number Diff line number Diff line change
Expand Up @@ -420,11 +420,15 @@ function serialize_any(s::SerializationState, x)
else
t.mutable && serialize_cycle(s, x) && return
serialize_type(s, t)
for i in 1:nf
if isdefined(x, i)
serialize(s, getfield(x, i))
else
writetag(s.io, UNDEFREF_TAG)
if t.pointerfree && ccall(:jl_datatype_haspadding, Cint, (Any,), t)==0
write(s.io, pointer_from_objref(x), sizeof(x))
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the pointer returned here may be to a box that is not gc-rooted. in general, pointer_from_objref should never be called on something that is immutable and pointerfree (I think we should make it an error)

i'm looking into possible alternatives that would provide the same benefit, but doesn't require calling pointer_from_objref

else
for i in 1:nf
if isdefined(x, i)
serialize(s, getfield(x, i))
else
writetag(s.io, UNDEFREF_TAG)
end
end
end
end
Expand Down Expand Up @@ -674,6 +678,11 @@ function deserialize(s::SerializationState, t::DataType)
end
if nf == 0
return ccall(:jl_new_struct, Any, (Any,Any...), t)
elseif t.pointerfree && ccall(:jl_datatype_haspadding, Cint, (Any,), t)==0
x = ccall(:jl_new_struct_uninit, Any, (Any,), t)
a_ = pointer_to_array(convert(Ptr{UInt8},pointer_from_objref(x)), sizeof(t))
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This is regrettable but there are no read! methods that accept a pointer.

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i've thought they should be unsafe_read! and implemented consistently instead of the current ad-hoc implementations

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Sounds good to me.

read!(s.io, a_)
return x
elseif isbits(t)
if nf == 1
return ccall(:jl_new_struct, Any, (Any,Any...), t, deserialize(s))
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5 changes: 5 additions & 0 deletions src/alloc.c
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Expand Up @@ -237,6 +237,11 @@ JL_DLLEXPORT int jl_field_isdefined(jl_value_t *v, size_t i)
return 1;
}

JL_DLLEXPORT int jl_datatype_haspadding(jl_datatype_t *dt)
{
return dt->haspadding;
}

JL_DLLEXPORT jl_value_t *jl_new_struct(jl_datatype_t *type, ...)
{
if (type->instance != NULL) return type->instance;
Expand Down