java - Concurrent ArrayList -

java - Concurrent ArrayList -

i need arraylist-like construction allowing next operations

get(int index) add(e element) set(int index, e element) iterator()

because of iterator beingness used in many places, using collections#synchronizedlist error-prone. list can grow few one thousand elements , gets used lot, i'm pretty sure, copyonwritearraylist slow. i'll start avoid premature optimizations, i'd bet won't work well.

most accesses single-threaded reads. i'm asking what's proper info construction this.

i though wrapping synchronizedlist in providing synchronized iterator do, won't because of concurrentmodificationexception. concenrning concurrent behavior, need changes visible subsequent reads , iterators.

the iterator doesn't have show consistent snapshot, may or may not see updates via set(int index, e element) operation gets used replace item updated version (containing added information, irrelevant user of iterator). items immutable.

i stated why copyonwritearraylist not do. concurrentlinkedqueue out of question lacks indexed access. need couple of operations rather fledged arraylist. unless any java concurrent list-related question duplicate of this question, 1 not.

in case can utilize readwritelock access backed list, allows multiple threads read list. if 1 thread needs write access reader-thread must wait operation complete. javadoc make's clear:

a readwritelock maintains pair of associated locks, 1 read-only operations , 1 writing. read lock may held simultaneously multiple reader threads, long there no writers. write lock exclusive.

here sample:

public class concurrentarraylist<t> { /** utilize lock write operations add/remove */ private final lock readlock; /** utilize lock read operations get/iterator/contains.. */ private final lock writelock; /** underlying list*/ private final list<t> list = new arraylist(); { reentrantreadwritelock rwlock = new reentrantreadwritelock(); readlock = rwlock.readlock(); writelock = rwlock.writelock(); } public void add(t e){ writelock.lock(); try{ list.add(e); }finally{ writelock.unlock(); } } public void get(int index){ readlock.lock(); try{ list.get(index); }finally{ readlock.unlock(); } } public iterator<t> iterator(){ readlock.lock(); seek { homecoming new arraylist<t>( list ).iterator(); //^ iterate on snapshot of our list } finally{ readlock.unlock(); } }

java arraylist concurrency