Detemining queue size

Question

I have to implement a queue to which object will be added and removed by two different threads at different time based on some factor.My problem is the requirement says the queue( whole queue and data it hold) should not take 200KB+ data .If size is 200 thread should wait for space to be available to push more data.Object pushed may vary in size.I can create java queue obut the size of queue will return the total object pushed instead of total memory used How do i determine the totla size of data my queue is refering to .

Consider the object pushed as

    class A{
       int x;
       byte[] buf;//array size vary per object
    }

you can do something like described in here: http://stackoverflow.com/questions/52353/in-java-what-is-the-best-way-to-determine-the-size-of-an-object — Farlan, May 30 '13 at 16:58
It doesn't look to me like ArrayBlockignQueue includes this functionality. (It seems it has a fixed element count, not fixed size.) — David Ogren, May 30 '13 at 17:01

score 0 · Answer 1 · edited May 23 '17 at 12:05

There is no out of the box functionality for this in Java. (In part, because there is no easy way to know if the objects added to the collection are referenced elsewhere and therefore if adding them takes up additional memory.)

For your use case, you would probably be best of just subclassing queue. Override the super to add the size of the object to a counter (obviously you will have to make this calculation thread safe.) and to throw an exception IllegalStateException if it doesn't have room. Similarly decrement your counter if on an overridden remove class.

The method of determining how to much space to add to the counter could vary. Farlan suggested using this and that looks like it would work. But since you are suggesting that you are dealing with a byte array, the size of the data you are adding might already be known to you. You will also have to consider whether you want to consider any of the overhead. The object takes some space, as does the reference inside of the queue itself. Plus the queue object. You could figure out exact values for that, but since it seems like your requirement is just to prevent outofmemory, you could probably just use rough estimates for those as long as you are consistent.

The details of what queue class you want to subclass may depend on how much contention you think there will be between the threads. But it sounds like you have a handle on the sync issues.

Detemining queue size

1 Answers1