RFR : 8016446 : (m) Add override forEach/replaceAll to HashMap, Hashtable, IdentityHashMap, WeakHashMap, TreeMap

[Mike Duigou]

On Jun 13 2013, at 06:21 , Remi Forax wrote:

> On 06/13/2013 07:28 AM, Mike Duigou wrote:
>> I have updated my webrev with Remi's improvements and some other improvements to the fast-fail concurrent modification checking.
>> 
>> Revised webrev:
>> 
>> http://cr.openjdk.java.net/~mduigou/JDK-8016446/1/webrev/
>> 
>> Mike
> 
> Hi Mike,
> 
> in TreeMap.forEach (and replaceAll), the check for co-modification should be done *before* action.accept(...)
> and not after because the semantics of the Iterator allows users to modify the map (hashmap or treemap)
> if it's the last element (so we should not check modCount after the last element).

Not implementing the best "fast-fail" we can to emulate the weaker semantics of iterator seems like a disservice.

> Also the code of forEach inside the loop is basically a hand-inlined version of Treemap.successor(),

> I wonder if it's not better to use successor() here ?

A little microbenchmark indicates that successor() is not appreciably slower and a lot clearer.

> 
> 
> in Hashtable.replaceAll(), the cast to K and V in function.apply() is useless.

Fixed. I had moved the casts around and didn't notice that these ones were no longer needed.

> otherwise, all other codes are ok for me :)
> 
> Rémi
> 
>> 
>> 
>> On Jun 12 2013, at 15:49 , Remi Forax wrote:
>> 
>>> On 06/12/2013 11:23 PM, Mike Duigou wrote:
>>>> Hello all;
>>>> 
>>>> This patch adds optimized implementations of Map.forEach and Map.replaceAll to HashMap, Hashtable, IdentityHashMap, WeakHashMap, TreeMap
>>>> 
>>>> http://cr.openjdk.java.net/~mduigou/JDK-8016446/0/webrev/
>>>> 
>>>> The implementations traverse the map more efficiently than the default iterator implementation and sometimes avoid creation of transient Map.Entry instances. The fast-fail behaviour of the default implementation is retained.
>>>> 
>>>> Mike
>>> Hi Mike,
>>> funnily I was writing HashMap.forEach/LinkedHashMap.forEach at the same time.
>>> (you need also to override forEach in LinkedHashMap because the one you inherits from HashMap doesn't use the linked list of entries).
>>> 
>>> My code is slightly different from yours because I've moved the cases where the item is a red/black tree out of the fast path
>>> (the tree is created either if you are unlucky, if hashCode is badly written or if someone forge keys to have collisions)
>>> and does the modCount check for each element because a call to the consumer can change the underlying map
>>> so you can not do a modCount check only at the end.
>>> 
>>> Rémi
>>> 
>>> Here is the diff.
>>> diff -r 6df79b7bae6f src/share/classes/java/util/HashMap.java
>>> --- a/src/share/classes/java/util/HashMap.java    Wed Jun 12 09:44:34 2013 +0100
>>> +++ b/src/share/classes/java/util/HashMap.java    Thu Jun 13 00:46:05 2013 +0200
>>> @@ -28,6 +28,7 @@
>>> import java.io.*;
>>> import java.lang.reflect.ParameterizedType;
>>> import java.lang.reflect.Type;
>>> +import java.util.function.BiConsumer;
>>> import java.util.function.Consumer;
>>> import java.util.function.BiFunction;
>>> import java.util.function.Function;
>>> @@ -2615,6 +2616,54 @@
>>>     int   capacity()     { return table.length; }
>>>     float loadFactor()   { return loadFactor;   }
>>> 
>>> +
>>> +    @Override
>>> +    public void forEach(BiConsumer<? super K, ? super V> action) {
>>> +        Objects.requireNonNull(action);
>>> +        final int expectedModCount = modCount;
>>> +        if (nullKeyEntry != null) {
>>> +            forEachNullKey(expectedModCount, action);
>>> +        }
>>> +        Object[] table = this.table;
>>> +        for(int index = 0; index < table.length; index++) {
>>> +            Object item = table[index];
>>> +            if (item == null) {
>>> +                continue;
>>> +            }
>>> +            if (item instanceof HashMap.TreeBin) {
>>> +                eachTreeNode(expectedModCount, ((TreeBin)item).first, action);
>>> +                continue;
>>> +            }
>>> +            @SuppressWarnings("unchecked")
>>> +            Entry<K,V> entry = (Entry<K,V>)item;
>>> +            for (;entry != null; entry = (Entry<K,V>)entry.next) {
>>> +                if (expectedModCount != modCount) {
>>> +                    throw new ConcurrentModificationException();
>>> +                }
>>> +                action.accept(entry.key, entry.value);
>>> +            }
>>> +        }
>>> +    }
>>> +
>>> +    private void eachTreeNode(int expectedModCount, TreeNode<K,V> node, BiConsumer<? super K, ? super V> action) {
>>> +        while (node != null) {
>>> +            if (expectedModCount != modCount) {
>>> +                throw new ConcurrentModificationException();
>>> +            }
>>> +            @SuppressWarnings("unchecked")
>>> +            Entry<K,V> entry = (Entry<K,V>)node.entry;
>>> +            action.accept(entry.key, entry.value);
>>> +            node = (TreeNode<K,V>)entry.next;
>>> +        }
>>> +    }
>>> +
>>> +    private void forEachNullKey(int expectedModCount, BiConsumer<? super K, ? super V> action) {
>>> +        if (expectedModCount != modCount) {
>>> +            throw new ConcurrentModificationException();
>>> +        }
>>> +        action.accept(null, nullKeyEntry.value);
>>> +    }
>>> +
>>>     /**
>>>      * Standin until HM overhaul; based loosely on Weak and Identity HM.
>>>      */
>>> diff -r 6df79b7bae6f src/share/classes/java/util/LinkedHashMap.java
>>> --- a/src/share/classes/java/util/LinkedHashMap.java    Wed Jun 12 09:44:34 2013 +0100
>>> +++ b/src/share/classes/java/util/LinkedHashMap.java    Thu Jun 13 00:46:05 2013 +0200
>>> @@ -24,7 +24,8 @@
>>>  */
>>> 
>>> package java.util;
>>> -import java.io.*;
>>> +
>>> +import java.util.function.BiConsumer;
>>> 
>>> /**
>>>  * <p>Hash table and linked list implementation of the <tt>Map</tt> interface,
>>> @@ -470,4 +471,16 @@
>>>     protected boolean removeEldestEntry(Map.Entry<K,V> eldest) {
>>>         return false;
>>>     }
>>> +
>>> +    @Override
>>> +    public void forEach(BiConsumer<? super K, ? super V> action) {
>>> +        Objects.requireNonNull(action);
>>> +        int expectedModCount = modCount;
>>> +        for (Entry<K,V> entry = header.after; entry != header; entry = entry.after) {
>>> +            if (expectedModCount != modCount) {
>>> +                throw new ConcurrentModificationException();
>>> +            }
>>> +            action.accept(entry.key, entry.value);
>>> +        }
>>> +    }
>>> }
>>> 
>>> 
>