lingbin commented on a change in pull request #2969: Fixed the move-assigment
of `Status`
URL: https://github.com/apache/incubator-doris/pull/2969#discussion_r382889942
##########
File path: be/src/common/status.h
##########
@@ -17,114 +17,136 @@ namespace doris {
class Status {
public:
- Status(): _state(nullptr) {}
+ Status() : _state(nullptr) { }
~Status() noexcept { delete[] _state; }
- // copy c'tor makes copy of error detail so Status can be returned by value
- Status(const Status& s)
- : _state(s._state == nullptr ? nullptr : copy_state(s._state)) {
- }
+ // Here _state == nullptr(Status::OK) is the most common case, so use this
as
+ // a fast path. This check can avoid one function call in most cases,
because
+ // _copy_state() is not an inline function.
+ Status(const Status& s) : _state(s._state == nullptr ? nullptr :
_copy_state(s._state)) { }
// same as copy c'tor
Status& operator=(const Status& s) {
// The following condition catches both aliasing (when this == &s),
// and the common case where both s and *this are OK.
if (_state != s._state) {
delete[] _state;
- _state = (s._state == nullptr) ? nullptr : copy_state(s._state);
+ _state = (s._state == nullptr) ? nullptr : _copy_state(s._state);
}
return *this;
}
- // move c'tor
Status(Status&& s) noexcept : _state(s._state) {
s._state = nullptr;
}
- // move assign
Status& operator=(Status&& s) noexcept {
- std::swap(_state, s._state);
+ if (_state != s._state) {
Review comment:
There are no requirements and also no prohibitions in the standard.
But for `dest = std::move(src)`, the following two points are determined:
1. the `dest` resource should **not** be assigned to `src` after
move-assignment.
2. The move-assignment of move-constructor should have the **same behavior**.
And for `Status`, it only has one member, `_state`, which is **pointer
type**.
when the `src::_state` was moved to `dest`, it must be cleared in `src`,
otherwise, **the pointer will be referenced by both the `src` and `dest`, which
will be wrong.**
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