stm.java

AtomicReference<Map> amap;

readOnlyMethod() {
   // get immutable map reference
   Map m = amap.get();
   m.get(key);
   ...
   m.get(key2);
   ...
}

writeMethod() {
    boolean success = false;
    // retry ALL operations if map has changed while we were updating
    while(!success) {
        // get immutable map reference
        Map original = amap.get();
        // create a copy
        Map updated = new Map(original); 
        // modify map
        updated.put(key, value);
        ...
        // here we can use data from map, of course
        // this is one of the reasons we have to retry
        // basically it's like a transaction. That's why it's called Software Transactional Memory
        if(updated.get(key1).equals(something)) {
            updated.put(key2, value2);
        }

        //save new map
        success = amap.cas(original, updated);
        // here we can add some randomized algorithm for back off *if writes are frequent*
        Thread.sleep(System.currentTimeMillis() % 5);
    }
}