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

Ivan Gerasimov ivan.gerasimov at oracle.com
Tue Apr 2 21:34:50 UTC 2013

Thank you Stanimir!

My main goal was to get rid of early and possibly unneeded memory allocation. I thought that System.arraycopy() would somehow compensate the need to traverse the array twice. However testing shows that my code works a bit faster at least when dealing with Integer arrays of size from 1 to 100.

Sincerely, Ivan

On 02.04.2013 23:25, Stanimir Simeonoff wrote:

The current version is cache oblivious. In any case for smaller arrays (like COW) System.arrayCopy won't yield any noticeable difference. Also, iirc System.arrayCopy places a memory barrier which in the COW case is unneeded.

Stanimir

On Tue, Apr 2, 2013 at 9:53 PM, Ivan Gerasimov <ivan.gerasimov at oracle.com <mailto:ivan.gerasimov at oracle.com>> wrote: Hello everybody! Please review my proposal for the CopyOnWriteArrayList.addIfAbsent() method optimization. http://washi.ru.oracle.com/~igerasim/webrevs/8011215/webrev/index.html <http://washi.ru.oracle.com/%7Eigerasim/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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