How to deallocate dynamic memory shared by two threads?

Question

Programming

The main thread creates a dynamic array. Then a detached thread is created that uses this dynamic array.

int *arr[N];
...
thread thr(Daughter);
thr.detach(); 
...
delete[] arr;

The child thread periodically checks for a flag that the main thread can set. When the flag is set, the child thread exits.
If the main thread decides to terminate itself and the work of the child thread, sets the child thread's termination flag, and immediately starts freeing memory, then an error may occur, since the child thread does not immediately stop and can access the freed memory.
How and when to free memory?
It should be noted that the child thread itself cannot free the memory, since it can be claimed in the main thread even after the completion of the child.

Answer 1

This is not C ++, but the essence should be clear.