Not thread safe methods of CuncurrentSkipListMap in Java

Question

In my Java project I need to use TreeMap in multihreaded way. I found that ConcurrentSkipListMap is what that I need but some methods are not thread safe. One of them - containsKey(Object key). What is a typical solution for using this methods in multhreded way? In my program I need put key that will not replace old and if it's impossible I will be putting another key while will not get unique key. What construction should use instead containsKey as i can't lost information?

Answer 1

If you are worried about containsKey results going stale before you can act on them, or about this warning in the javadoc:

Additionally, the bulk operations putAll, equals, toArray, containsValue, and clear are not guaranteed to be performed atomically. For example, an iterator operating concurrently with a putAll operation might view only some of the added elements.

there are methods defined on ConcurrentSkipListMap that you can use instead. For instance, see putIfAbsent:

If the specified key is not already associated with a value, associate it with the given value. This is equivalent to

if (!map.containsKey(key))
    return map.put(key, value);
else
    return map.get(key);

except that the action is performed atomically.

Also see the methods remove and replace.