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package com.bazaarvoice.ostrich;

import java.io.Closeable;
import java.util.Collection;
import java.util.concurrent.Future;

/**
 * An asynchronous service pool.  This mimics the behavior of a {@link ServicePool}, but instead of executing its
 * callbacks synchronously, it will run them in the background.
 *
 * @param  The service interface that this pool keeps track of end points for.
 */
public interface AsyncServicePool extends Closeable {
    /**
     * Execute a request asynchronously against one of the remote services in this {@code ServicePool}, returning
     * a future representing the asynchronous call.
     *
     * @param retryPolicy The retry policy for the operation.
     * @param callback    The user provided callback to invoke.
     * @param          The return type for the call.
     * @return            A future representing the call.
     */
     Future execute(RetryPolicy retryPolicy, ServiceCallback callback);

    /**
     * Execute a request asynchronously against one of the remote services in this {@code ServicePool} using the
     * specified partition information to narrow down the suitable service end points.
     *
     * @param partitionContext The partition context.
     * @param retryPolicy      The retry policy for the operation.
     * @param callback         The user provided callback to invoke with a service end point.
     * @param               The return type for the call.
     * @return                 A future representing the call.
     */
     Future execute(PartitionContext partitionContext, RetryPolicy retryPolicy, ServiceCallback callback);

    /**
     * Execute a request asynchronously against ALL of the remote services in this {@code ServicePool},
     * returning a future for each asynchronous call.
     * 
     * NOTE: It is undefined how the implementation handles the situation where an end point is discovered or removed
     * while the {@code executeOnAll} operation is executing.
     *
     * @param retryPolicy The retry policy for each operation.
     * @param callback    The user provided callback to invoke.
     * @param          The return type for the call.
     * @return            A collection with one future for each end point being called.
     */
     Collection> executeOnAll(RetryPolicy retryPolicy, ServiceCallback callback);

    /**
     * Execute a request asynchronously against some of the remote services in this {@code ServicePool},
     * returning a future for each asynchronous call.
     * 

     * NOTE: It is undefined how the implementation handles the situation where an end point is discovered or removed
     * while the {@code executeOn} operation is executing.
     *
     * @param predicate   A predicate indicating which service end points the request should be executed against.  If
     *                    the predicate returns {@code true} then the request will be executed against that end point.
     * @param retryPolicy The retry policy for each operation.
     * @param callback    The user provided callback to invoke.
     * @param          The return type for the call.
     * @return            A collection with one future for each end point being called.
     */
     Collection> executeOn(ServiceEndPointPredicate predicate, RetryPolicy retryPolicy,
                                        ServiceCallback callback);

    /**
     * Return the number of valid end points that this service pool knows about.  This will include end points that have
     * never thrown exceptions during execution (even those that have never been interacted with) and end points that
     * were previously known as bad but have since had a successful health check.  If this method returns non-zero, then
     * a call to execute should not fail with an {@link com.bazaarvoice.ostrich.exceptions.OnlyBadHostsException} or
     * {@link com.bazaarvoice.ostrich.exceptions.NoAvailableHostsException} exception.
     */
    int getNumValidEndPoints();

    /**
     * Return the number of end points that this service pool considers to be in a bad state.  A bad end point is one
     * that a previous operation was attempted on and the attempt failed.  An end point could be considered bad prior to
     * its health check being called.
     * 
     * This combined with {@link #getNumValidEndPoints()} gives visibility into the total number of end points that the
     * {@code ServicePool} knows about.
     */
    int getNumBadEndPoints();
}