On Apr 8 2013, at 14:09 , Peter Levart wrote:
> Hi Mike,
>
> It's unfortunate that getOrDefault() is specified so that it can't be
> implemented atomically in terms of existent (non-default) ConcurrentMap
> methods, so platform ConcurrentMap implementations will have atomic
> implementation and others will have to catch-up first. I hope this will not
> be a cause of any concurrency bugs.
The only solution I can see is to provide a default in ConcurrentMap that uses
only get() and documents that implementations supporting null values will will
need to override the default. I will include this in the updated webrev.
This may not be as radical as it sounds. Doug has said that he knows of no
ConcurrentMap implementations that support null keys/values. (Why would anyone
want to)
> The javadoc for computeIfPresent seems to be inconsistent:
>
> 826 * If the value for the specified key is present and non-null,
> 827 * attempts to compute a new mapping given the key and its current
> 828 * mapped value.
> 829 *
> 830 * <p>If the function returns {@code null}, the mapping is removed
> (or
> 831 * remains absent if initially absent). If the function itself
> throws an
> 832 * (unchecked) exception, the exception is rethrown, and the current
> mapping
> 833 * is left unchanged.
>
> I think the situation described in bold is non-existent.
Corrected.
>
> Regards, Peter
>
>
> On 04/08/2013 08:07 PM, Mike Duigou wrote:
>> Hello all;
>>
>> This is a combined review for the new default methods on the java.util.Map
>> interface being added for the JSR-335 lambda libraries. The reviews are
>> being combined because they share a common unit test.
>>
>> http://cr.openjdk.java.net/~mduigou/JDK-8010122/0/webrev/
>>
>> 8004518: Add in-place operations to Map
>> forEach()
>> replaceAll()
>>
>> 8010122: Add atomic operations to Map
>> getOrDefault()
>> putIfAbsent() *
>> remove(K, V)
>> replace(K, V)
>> replace(K, V, V)
>> compute() *
>> merge() *
>> computeIfAbsent() *
>> computeIfPresent() *
>>
>> The * operations treat null values as being absent. (ie. the same as there
>> being no mapping for the specified key).
>>
>> The default implementations provided in Map are overridden in HashMap for
>> performance purposes, in Hashtable for atomicity and performance purposes
>> and in Collections for atomicity.
>>
>> Mike
>>
>
