zclllyybb commented on code in PR #35126:
URL: https://github.com/apache/doris/pull/35126#discussion_r1607934315
##########
be/src/util/once.h:
##########
@@ -52,14 +52,36 @@ class DorisCallOnce {
public:
DorisCallOnce() : _has_called(false) {}
+ // this method is not exception safe, it will core when exception occurs in
+ // callback method. I have tested the code
https://en.cppreference.com/w/cpp/thread/call_once.
// If the underlying `once_flag` has yet to be invoked, invokes the
provided
// lambda and stores its return value. Otherwise, returns the stored
Status.
+ // template <typename Fn>
+ // ReturnType call(Fn fn) {
+ // std::call_once(_once_flag, [this, fn] {
+ // _status = fn();
+ // _has_called.store(true, std::memory_order_release);
+ // });
+ // return _status;
+ // }
+
+ // If the underlying `once_flag` has yet to be invoked, invokes the
provided
+ // lambda and stores its return value. Otherwise, returns the stored
Status.
+ // If exception occurs in the function, the call flag is not set, user
could call
+ // it again. like std::call_once.
template <typename Fn>
ReturnType call(Fn fn) {
- std::call_once(_once_flag, [this, fn] {
- _status = fn();
- _has_called.store(true, std::memory_order_release);
- });
+ if (has_called()) {
+ return _status;
+ }
+ std::lock_guard l(_flag_lock);
+ // After lock, should check again. Another thread may call
+ // at the same time during first time check has called.
+ if (has_called()) {
+ return _status;
+ }
+ _status = fn();
+ _has_called.store(true, std::memory_order_release);
Review Comment:
should `store` then `fn()`?
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