Compares the variable associated with the key with old_value and if it matches then assigns the new_value to it.
The key that is used to store the variable in the cache. key is case sensitive.
Old value of the variable pointed by key in the user cache. The value should be of type long, otherwise the function returns false.
New value which will get assigned to variable pointer by key if a match is found. The value should be of type long, otherwise the function returns false.
Returns true on success or false on failure.