Java synchronization problem

Question

Hi,

I have two threads and one class.

Thread1 updates the local object of the class via 3 different methods. The local object (behind the scene) uses some sort of ArrayList to store data. Three methods (mentioned earlier), are doing something with elements of the list...

Thread2 queries the local object (content of array list).

PROBLEM: How can I make sure that none of the three updating methods (Thread1) will modify the content of the "local object" while it's being read by Thread2?

Thanks

Answer 1

You can make the methods which access the data (read or write) 'synchronized'.

Answer 2

In all methods mentionned above use a synchronized(your_list) { ... code ... } context, making the methods synchronized is a maybe to hard solution, blocks more than needed if you just want to protect the list and not the whole object.

Answer 3

Put a common lock around portions of the code that modify the ArrayList using synchronized. It doesn't really matter what object you use as a lock, as long as it's the same, but I think using the ArrayList itself would be idiomatic:

synchronized (list) {
   list.put()...
}

synchronized (list) {
   list.get()...
}

Answer 4

Using synchronized keyword. You are dealing with problem known as critical sections

Answer 5

I suggest you read the Java Tutorial on Concurrency, in particular the section on synchronization. You have a straightforward case of synchronization.