删除线程安全吗？

Question

int *p = new int;
// delete p in thread 1
// delete p in thread 2

I know that make p equals to nullptr is a good behavior but for now I just want to know if delete is thread-safe? Do I need to use lock for the case above?

Yes, I delete the same object twice.

This is because that I found that delete p twice in the same thread would make a core dumped error, whereas delete p twice in two threads can not make any error.

I know that double delete is an UB so I want to know if delete is thread-safe, meaning that if we enter the function delete twice at the same time, we are safe because of it is thread-safe.

Answer 1

You can use the following approach to achieve what you want by using a synchronization mechanism: Make sure that the deletion of p and setting it to nullptr can only be done by a single thread at a given moment:

// multiple threads
// ...
// single thread (critical region)
delete p;
p = nullptr;
// multiple threads
// ...

This way, a second delete by another thread does nothing, since nullptr will be what is going to be passed to delete .