CODEWITHSUNDEEP
javaserializationconcurrency
farm ostrich
farm ostrich

Reputation: 5959

Java serialization causes concurrency modification exception

My program updates several hundred objects stored in an ArrayList about one hundred times per second. I've implemented Java's built in serialization, and it works well except when an attempt to serialize is made when the objects are going at it, in which case I may have to serialize a half dozen times before it works (each failed attempt throws an exception). I tried marking the arraylist as transient, but then when I loaded the serialization file, a null pointer exception is thrown. So I tried initializing the transient arraylist in the no args constructor, which did nothing to help. What do I do? Thanks.

Upvotes: 1

Views: 2196

Answers (5)

Jed Wesley-Smith
Jed Wesley-Smith

Reputation: 4706

Assuming you really don't want or need the list contents serialised declare your list member:

private transient final List<?> things = new ArrayList<Object>();

You will always have a non-null list to work with.

That being said, from the sound of it your updates to the list itself may need to be thought about regarding other thread-safety issues such data-races and visibility issues.

Upvotes: 0

Rakesh
Rakesh

Reputation: 365

Use the Iterator if you are traversing through the collection and concurrently modifying it.

Upvotes: 0

WhiteFang34
WhiteFang34

Reputation: 72039

First make sure you've synchronized access to your ArrayList, e.g. when you initialize it:

List<String> list = Collections.synchronizedList(new ArrayList<String>());

When you need to serialize it, grab a copy that will be consistent due to the synchronization:

List<String> copy = new ArrayList<String>(list);

Now you can safely serialize out this copy without blocking access to the primary list.

Upvotes: 4

Jim Blackler
Jim Blackler

Reputation: 23169

Copy the ArrayList to a new instance (shallow copy with new ArrayList<>() and serialize that.

Upvotes: 0

Marcin
Marcin

Reputation: 1615

You can't iterate with foreach statement and modify your table.

Try to use

for (int i =0;i<arra.length;i++)

instead.

Upvotes: 0

Related Questions