Examples of com.persistit.Accumulator$AccumulatorRef

com.persistit.Accumulator

Device that maintains a strong reference to the Accumulator when it contains updates and needs to be checkpointed, and a weak reference otherwise. The Persistit instance contains a collection of AccumulatorRef instances; these are used when determining which accumulators to include in the checkpoint operation. Once an Accumulator's checkpoint has been written, the strong reference is removed until there is a subsequent update.

Scenario: a process creates a new Tree, creates an Accumulator and then releases all references to the Tree. Eventually the Tree and the new Accumulator should be garbage collected; however, the Accumulator must be retained until any values it has accumulated have been written as part of a checkpoint. The dual references in this class are intended to support this behavior; the _checkpointRef field is null whenever there are no changes to checkpoint; the _weakRef is used to detect when it is permissible to remove the AccumulatorRef from the Persistit instance's accumulator set.

import com.persistit.exception.PersistitInterruptedException;


public class AccumulatorAdapter {


    public static long getSnapshot(AccumInfo accumInfo, Tree tree) throws PersistitInterruptedException {
        Accumulator accumulator = getAccumulator(accumInfo, tree);
        return accumulator.getSnapshotValue();
    }

        Accumulator.SumAccumulator sum = (Accumulator.SumAccumulator)getAccumulator(accumInfo, exchange.getTree());
        sum.add(value);
    }
    
    public static long getLiveValue(AccumInfo accumInfo, Tree tree) {
        Accumulator accumulator = getAccumulator(accumInfo, tree);
        return accumulator.getLiveValue();
    }

Related Classes of com.persistit.Accumulator$AccumulatorRef

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