kou commented on code in PR #33847:
URL: https://github.com/apache/arrow/pull/33847#discussion_r1086237224
##########
cpp/src/arrow/type.h:
##########
@@ -288,31 +288,46 @@ std::shared_ptr<DataType> GetPhysicalType(const
std::shared_ptr<DataType>& type)
class ARROW_EXPORT FixedWidthType : public DataType {
public:
using DataType::DataType;
+ // This is only for preventing defining this class in each
+ // translation unit to avoid one-definition-rule violation.
+ ~FixedWidthType() override;
Review Comment:
To be honest, I don't know much about this but...
I tried to create a small example to reproduce this case but couldn't create
it... So I explain what I observed:
If we don't have this, `.o` of a C++ code that has
`std::make_shared<arrow::XXXType>` such as `std::make_shared<arrow::ListType>`
has the following `nm` result:
```console
$ nm --demangle
src/arrow/CMakeFiles/arrow_objlib.dir/compute/kernels/scalar_cast_numeric.cc.o
| grep 'vtable for arrow::FloatingPointType'
00000000 W vtable for arrow::FloatingPointType
```
`W` is a global weak symbol.
https://linux.die.net/man/1/nm
> If lowercase, the symbol is local; if uppercase, the symbol is global
(external).
> "W"
> "w"
>
> The symbol is a weak symbol that has not been specifically tagged as a
weak object symbol.
If we have this, the symbol becomes a undefined symbol:
```console
$ nm --demangle
src/arrow/CMakeFiles/arrow_objlib.dir/compute/kernels/scalar_cast_numeric.cc.o
| grep 'vtable for arrow::FloatingPointType'
U vtable for arrow::FloatingPointType
```
https://linux.die.net/man/1/nm
> "U"
>
> The symbol is undefined.
If there are multiple `W vtable for arrow::FloatingPointType` in our `.o`.
linking `libarrow.so` with `-flto` is failed:
```text
[650/1111] Linking CXX shared library debug/libarrow.so.1100.0.0
FAILED: debug/libarrow.so.1100.0.0
: && /bin/c++ -fPIC -Wno-noexcept-type -flto -fdiagnostics-color=always
-Wall -Wno-conversion -Wno-sign-conversion -Wunused-result
-fno-semantic-interposition -msse4.2 -g -Werror -O0 -ggdb -shared
-Wl,-soname,libarrow.so.1100 -o debug/libarrow.so.1100.0.0 ...(**/*.o)... && :
cpp/src/arrow/type.h:313: error: virtual table of type ‘struct
FloatingPointType’ violates one definition rule [-Werror=odr]
313 | class ARROW_EXPORT FloatingPointType : public NumberType {
|
cpp/src/arrow/type.h:313:20: note: the conflicting type defined in another
translation unit
313 | class ARROW_EXPORT FloatingPointType : public NumberType {
| ^
<built-in>: note: virtual method ‘__cxa_pure_virtual’
...
```
It seems that `W` and `-flto` is a bad combination. If we change `W` to `U`
by defining a not-inlined deconstructor, we don't get the ODR error.
Do you notice anything from this observation?
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