Hello,

 let x = Array.make 100 []
 let update i n = x.(i) <- n :: x.(i)
 let read i = x.(i)

 Consider the following scenario: one thread is `update`ing x, another
thread(s) uses only `read`. Is it safe to use these functions without
locking on mutex? 

 I.e. is Array.set atomic? What about updating references (:=) ?

 If I understand correctly these operations require only one cpu
instruction to update one machine word and so should be atomic. Taking
into account "single-cpu affinity" of ocaml program it should be safe
to write such multithreaded code. Is it true?

 Is it safe to assume that ocamlopt won't skip reads/writes to globally
visible memory address using cached value in a register?

-- 
 ygrek
 http://ygrek.org.ua