flowcontrolmanager.cc

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/*
 * Copyright (c) 2013-2014,2016 - Adjacent Link LLC, Bridgewater, New
 * Jersey
 * Copyright (c) 2010 - DRS CenGen, LLC, Columbia, Maryland
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * * Redistributions of source code must retain the above copyright
 *   notice, this list of conditions and the following disclaimer.
 * * Redistributions in binary form must reproduce the above copyright
 *   notice, this list of conditions and the following disclaimer in
 *   the documentation and/or other materials provided with the
 *   distribution.
 * * Neither the name of DRS CenGen, LLC nor the names of its
 *   contributors may be used to endorse or promote products derived
 *   from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
 * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
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 * ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 */

#include "emane/flowcontrolmanager.h"

#include <mutex>

class EMANE::FlowControlManager::Implementation
{
public:
Implementation(EMANE::DownstreamTransport & transport):
  rTransport_(transport),
  u16TokensAvailable_{},
  u16TotalTokensAvailable_{},
  u16ShadowTokenCount_{},
  u16LastTokensUpdate_{},
  bAckPending_{true}{}

  ~Implementation(){}

  void start(std::uint16_t u16TotalTokensAvailable)
  {
    std::lock_guard<std::mutex> m(mutex_);

    u16TotalTokensAvailable_ = u16TotalTokensAvailable;
    u16TokensAvailable_      = u16TotalTokensAvailable;

    sendFlowControlResponseMessage();
  }

  void stop()
  {
    std::lock_guard<std::mutex> m(mutex_);

    u16TotalTokensAvailable_ = 0;
    u16TokensAvailable_      = 0;
    u16ShadowTokenCount_     = 0;
  }

  std::pair<std::uint16_t,bool> addToken(std::uint16_t u16Tokens)
  {
    std::lock_guard<std::mutex> m(mutex_);

  // get add tokens status
  const bool bStatus = ((u16TokensAvailable_ + u16Tokens) <= u16TotalTokensAvailable_);

  // have room to add all requested tokens
  if(bStatus == true)
    {
      // update tokens available
      u16TokensAvailable_ += u16Tokens;
    }

  // check shadow count, send update if tokens are available
  if((u16ShadowTokenCount_ == 0) && (u16TokensAvailable_ > 0))
    {
      sendFlowControlResponseMessage();
    }

  return {u16TokensAvailable_,bStatus};
  }

  std::pair<std::uint16_t,bool> removeToken()
  {
    std::lock_guard<std::mutex> m(mutex_);

    bool bStatus;

    // ack pending, no action
    if(bAckPending_ == true)
      {
        bStatus = false;
      }
    else
      {
        // no tokens available
        if(u16TokensAvailable_ == 0)
          {
            bStatus = false;
        }
        else
          {
            // decrement tokens available
            --u16TokensAvailable_;
            --u16ShadowTokenCount_;

            bStatus = true;
          }
      }

    return {u16TokensAvailable_,bStatus};
  }

  void processFlowControlMessage(const Controls::FlowControlControlMessage * pMsg)
  {
    std::lock_guard<std::mutex> m(mutex_);

    if(!bAckPending_)
      {
        // upstream layer start or restart condition
        // detected
        sendFlowControlResponseMessage();
      }
    else
      {
        // a proper acknowledgment echos the token account will allow
        // traffic to flow
        if(pMsg->getTokens() == u16LastTokensUpdate_)
          {
            bAckPending_ = false;
          }
        else
          {
            // upstream layer missed the initial token message
            // so we received a message with an incorrect number token
            // count - resend a reponse
            sendFlowControlResponseMessage();
          }
      }
  }

private:

  DownstreamTransport & rTransport_;

  std::mutex mutex_;

  std::uint16_t u16TokensAvailable_;

  std::uint16_t u16TotalTokensAvailable_;

  std::uint16_t u16ShadowTokenCount_;

  std::uint16_t u16LastTokensUpdate_;

  bool bAckPending_;

  // precondition - mutex is locked
  void sendFlowControlResponseMessage()
  {
    rTransport_.sendUpstreamControl({Controls::FlowControlControlMessage::create(u16TokensAvailable_)});

    u16ShadowTokenCount_ = u16TokensAvailable_;

    u16LastTokensUpdate_ = u16TokensAvailable_;

    bAckPending_ = true;
  }
};


EMANE::FlowControlManager::FlowControlManager(DownstreamTransport & transport):
  pImpl_{new Implementation{transport}}
{}

EMANE::FlowControlManager::~FlowControlManager(){}

void EMANE::FlowControlManager::start(std::uint16_t u16TotalTokensAvailable)
{
  pImpl_->start(u16TotalTokensAvailable);
}

void EMANE::FlowControlManager::stop()
{
  pImpl_->stop();
}

std::pair<std::uint16_t,bool> EMANE::FlowControlManager::addToken(std::uint16_t u16Tokens)
{
  return pImpl_->addToken(u16Tokens);
}

std::pair<std::uint16_t,bool> EMANE::FlowControlManager::removeToken()
{
  return pImpl_->removeToken();
}

void EMANE::FlowControlManager::processFlowControlMessage(const Controls::FlowControlControlMessage * pMsg)
{
  pImpl_->processFlowControlMessage(pMsg);
}