1 is not really an issue. Each request checks the cache. If it is not there,
it is updated so the next thread gets the updated copy. (for the most part -
there is a nasty concurrency issue that we'll tackle in 2)

2 you will need to wrap the cache object with a function that locks the
cache when it is being written. This will block other threads while the data
is updated. If the update is not frequent, this is not a problem. however,
if it is or if there are a lot of cache misses, you could bottle neck. One
solution is to lock on a string object that represents the cache. This is
much cheaper than locking on the cache object itself. so essentially, the
string represents the cache. you lock the string and update the cache. there
is some slight overhead but it fairs rather well under moderate loads - at
least better than locking the cache object itself.