RFR [8011215] optimization of CopyOnWriteArrayList.addIfAbsent() (original) (raw)

Ivan Gerasimov ivan.gerasimov at oracle.com
Tue Apr 2 18:53:09 UTC 2013

Hello everybody!

Please review my proposal for the CopyOnWriteArrayList.addIfAbsent() method optimization.

http://washi.ru.oracle.com/~igerasim/webrevs/8011215/webrev/index.html

Here is the original function body:

 Object[] elements = getArray();
 int len = elements.length;
 Object[] newElements = new Object[len + 1]; <-- allocate new array in advance
 for (int i = 0; i < len; ++i) {
     if (eq(e, elements[i]))                 <-- check whether e is null on every iteration
         return false; // exit, throwing away copy
     else
         newElements[i] = elements[i];       <-- copy elements one by one
 }
 newElements[len] = e;
 setArray(newElements);

The proposed change is to reuse CopyOnWriteArrayList.indexOf() function to check if e is already in the array. If the check passed, new array is allocated withArrays.copyOf(). It uses native System.arraycopy(), which is probably faster than copying elements in the loop.

Sincerely yours, Ivan

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