MemoryConsumingTask.java

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package org.dcm4chee.task;

import java.util.concurrent.Callable;

/**
 * A task the consumes large amounts of memory.
 * <p>
 * The needed memory needs to be estimable BEFORE the task gets started.
 *
 * @param <V> <V> the result type of method {@link #call}
 *
 * @author Hermann Czedik-Eysenberg <hermann-agfa@czedik.net>
 */
public interface MemoryConsumingTask<V> extends Callable<V> {

    /**
     * @return type of the task. Typically one of {@link ImageProcessingTaskTypes}. (But extensible through the
     * interface {@link TaskType} for new types)
     */
    TaskType getTaskType();

    /**
     * Calculates the estimated weight of the task, i.e. maximum memory it will consume in bytes at any moment in time
     * during the invocation of its <code>call</code> method.
     * Of course, the estimation has to be done, without actually allocating this memory yet.
     * <p>
     * The information will be used by the executing {@link WeightWatcher} to apply memory and concurrency limits.
     * <p>
     * If the returned value is 0 then this means that no memory and concurrency limits should be
     * applied. This can be used to support the case where a task decides that it does not actually need to consume
     * a lot of memory (e.g. rendition not required, because rendered image loaded from cache).
     *
     * @return estimated weight of the task in bytes
     */
    long getEstimatedWeight();

    /**
     * Allocates memory and computes a result (or throws an exception if unable to do so).
     * <p>
     * BEFORE the end of this method all the used memory needs to be freed again (needs to be eligible for garbage
     * collection).
     *
     * @return computed result
     *
     * @throws Exception if unable to compute a result
     */
    @Override
    V call() throws Exception;

}