fix realloc size detection when new size is larger than current chunk max size, add pthread mutex to make the functions thread safe

main.c

@@ -5,6 +5,11 @@ int main(void)
 {
 	void *ptr;
 
+	printf("%zu\n", SMALL_CHUNK_SIZE);
 	ptr = malloc(1203);
+	show_alloc_mem();
+	ptr = realloc(ptr, 12045);
+	show_alloc_mem();
 	free(ptr);
+	show_alloc_mem();
 }