RC9/qpid/cpp/src/qpid/cluster/WriteEstimate.h

#ifndef QPID_CLUSTER_WRITEESTIMATE_H
#define QPID_CLUSTER_WRITEESTIMATE_H

/*
 *
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 * 
 *   http://www.apache.org/licenses/LICENSE-2.0
 * 
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 * KIND, either express or implied.  See the License for the
 * specific language governing permissions and limitations
 * under the License.
 *
 */

#include "qpid/sys/Mutex.h"

namespace qpid {
namespace cluster {

/**
 * Estimate the amount of data that a connection can write between sending
 * a doOutput notice and re-receiving it.
 *
 * The goal is to avoid ever write-idling the connection by sending
 * the next doOutput request as soon as we've processed the previous
 * one, such that data generated by the previous request will keep the
 * writer busy till the next one is delivered.
 *
 */
class WriteEstimate
{
  public:
    WriteEstimate(size_t initial=4096);

    /** About to send a doOutput request.
     * Update estimation state and return size for next request.
     */
    size_t sending(size_t buffered);

    /**
     * doOutput request just delivered, not yet executed. Update the estimate.
     * and estimate how much data to request in the next onOutput
     * request. 0 means don't send an onOutput request.
     *
     * @param delivered value in doOutput control.
     */
    void delivered(size_t delivered, size_t sent, size_t buffered);

    /** Last estimate delivered, i.e. known to cluster */
    size_t getLastEstimate() const { return estimate; }

  private:
    bool growing;
    size_t estimate, lastEstimate;
};

}} // namespace qpid::cluster

#endif  /*!QPID_CLUSTER_WRITEESTIMATE_H*/