C++ :: Multithread Application - Global Dynamic Array

Let's have global dynamic array p defined as

volatile int p[];

Let's use it in a multithread application, where every thread can change array's size by

new_p = realloc(p, new_size);
if (!new_p) exit 1;
p = new_p;

For simplify assume that we have no problems with it's size and indexing.

Expression like

int x = p[i];

is unsafe cause thread (1) takes the pointer and (2) add the index. Executing of this thread may be stoped after first step before second step. In this time other thread can realloc the array, which move it to some other place in memory. Executing second step after it will add index to wrong pointer. So we will have segmentation fault.