in listing_7.12.cpp in pop() #57
Description
"If two threads execute the pop() function one after another, and thread 1 finishes executing increase_head_count() first, resulting in its
old_head's external_count=2; immediately followed by thread 2 executing increase_head_count(), leading to its old_head's external_count=3, and the stack's head's external_count=3 as well. At this point, when thread 1 executes head.compare_exchange_strong(), it will fail. Is this an error?"