monero/src/cryptonote_basic/miner.cpp

// Copyright (c) 2014-2016, The Monero Project
//
// All rights reserved.
//
// Redistribution and use in source and binary forms, with or without modification, are
// permitted provided that the following conditions are met:
//
// 1. Redistributions of source code must retain the above copyright notice, this list of
//    conditions and the following disclaimer.
//
// 2. 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.
//
// 3. Neither the name of the copyright holder 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 LIMITED TO, THE IMPLIED WARRANTIES OF
// MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL
// THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
// PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
// INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
// STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF
// THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
//
// Parts of this file are originally copyright (c) 2012-2013 The Cryptonote developers

#include <sstream>
#include <numeric>
#include <boost/utility/value_init.hpp>
#include <boost/interprocess/detail/atomic.hpp>
#include <boost/limits.hpp>
#include "misc_language.h"
#include "include_base_utils.h"
#include "cryptonote_basic_impl.h"
#include "cryptonote_format_utils.h"
#include "file_io_utils.h"
#include "common/command_line.h"
#include "string_coding.h"
#include "storages/portable_storage_template_helper.h"

#undef MONERO_DEFAULT_LOG_CATEGORY
#define MONERO_DEFAULT_LOG_CATEGORY "miner"

using namespace epee;

#include "miner.h"


extern "C" void slow_hash_allocate_state();
extern "C" void slow_hash_free_state();
namespace cryptonote
{

  namespace
  {
    const command_line::arg_descriptor<std::string> arg_extra_messages =  {"extra-messages-file", "Specify file for extra messages to include into coinbase transactions", "", true};
    const command_line::arg_descriptor<std::string> arg_start_mining =    {"start-mining", "Specify wallet address to mining for", "", true};
    const command_line::arg_descriptor<uint32_t>      arg_mining_threads =  {"mining-threads", "Specify mining threads count", 0, true};
    const command_line::arg_descriptor<bool>        arg_bg_mining_enable =  {"bg-mining-enable", "enable/disable background mining", true, true};
    const command_line::arg_descriptor<uint64_t>    arg_bg_mining_min_idle_interval_seconds =  {"bg-mining-min-idle-interval", "Specify min lookback interval in seconds for determining idle state", miner::BACKGROUND_MINING_DEFAULT_MIN_IDLE_INTERVAL_IN_SECONDS, true};
    const command_line::arg_descriptor<uint8_t>     arg_bg_mining_idle_threshold_percentage =  {"bg-mining-idle-threshold", "Specify minimum avg idle percentage over lookback interval", miner::BACKGROUND_MINING_DEFAULT_IDLE_THRESHOLD_PERCENTAGE, true};
    const command_line::arg_descriptor<uint8_t>     arg_bg_mining_miner_target_percentage =  {"bg-mining-miner-target", "Specificy maximum percentage cpu use by miner(s)", miner::BACKGROUND_MINING_DEFAULT_MINING_TARGET_PERCENTAGE, true};
  }


  miner::miner(i_miner_handler* phandler):m_stop(1),
    m_template(boost::value_initialized<block>()),
    m_template_no(0),
    m_diffic(0),
    m_thread_index(0),
    m_phandler(phandler),
    m_height(0),
    m_pausers_count(0),
    m_threads_total(0),
    m_starter_nonce(0),
    m_last_hr_merge_time(0),
    m_hashes(0),
    m_do_print_hashrate(false),
    m_do_mining(false),
    m_current_hash_rate(0),
    m_is_background_mining_enabled(false),
    m_min_idle_seconds(BACKGROUND_MINING_DEFAULT_MIN_IDLE_INTERVAL_IN_SECONDS),
    m_idle_threshold(BACKGROUND_MINING_DEFAULT_IDLE_THRESHOLD_PERCENTAGE),
    m_mining_target(BACKGROUND_MINING_DEFAULT_MINING_TARGET_PERCENTAGE),
    m_miner_extra_sleep(BACKGROUND_MINING_DEFAULT_MINER_EXTRA_SLEEP_MILLIS)
  {

  }
  //-----------------------------------------------------------------------------------------------------
  miner::~miner()
  {
    stop();
  }
  //-----------------------------------------------------------------------------------------------------
  bool miner::set_block_template(const block& bl, const difficulty_type& di, uint64_t height)
  {
    CRITICAL_REGION_LOCAL(m_template_lock);
    m_template = bl;
    m_diffic = di;
    m_height = height;
    ++m_template_no;
    m_starter_nonce = crypto::rand<uint32_t>();
    return true;
  }
  //-----------------------------------------------------------------------------------------------------
  bool miner::on_block_chain_update()
  {
    if(!is_mining())
      return true;

    return request_block_template();
  }
  //-----------------------------------------------------------------------------------------------------
  bool miner::request_block_template()
  {
    block bl = AUTO_VAL_INIT(bl);
    difficulty_type di = AUTO_VAL_INIT(di);
    uint64_t height = AUTO_VAL_INIT(height);
    cryptonote::blobdata extra_nonce;
    if(m_extra_messages.size() && m_config.current_extra_message_index < m_extra_messages.size())
    {
      extra_nonce = m_extra_messages[m_config.current_extra_message_index];
    }

    if(!m_phandler->get_block_template(bl, m_mine_address, di, height, extra_nonce))
    {
      LOG_ERROR("Failed to get_block_template(), stopping mining");
      return false;
    }
    set_block_template(bl, di, height);
    return true;
  }
  //-----------------------------------------------------------------------------------------------------
  bool miner::on_idle()
  {
    m_update_block_template_interval.do_call([&](){
      if(is_mining())request_block_template();
      return true;
    });

    m_update_merge_hr_interval.do_call([&](){
      merge_hr();
      return true;
    });
    
    return true;
  }
  //-----------------------------------------------------------------------------------------------------
  void miner::do_print_hashrate(bool do_hr)
  {
    m_do_print_hashrate = do_hr;
  }
  //-----------------------------------------------------------------------------------------------------
  void miner::merge_hr()
  {
    if(m_last_hr_merge_time && is_mining())
    {
      m_current_hash_rate = m_hashes * 1000 / ((misc_utils::get_tick_count() - m_last_hr_merge_time + 1));
      CRITICAL_REGION_LOCAL(m_last_hash_rates_lock);
      m_last_hash_rates.push_back(m_current_hash_rate);
      if(m_last_hash_rates.size() > 19)
        m_last_hash_rates.pop_front();
      if(m_do_print_hashrate)
      {
        uint64_t total_hr = std::accumulate(m_last_hash_rates.begin(), m_last_hash_rates.end(), 0);
        float hr = static_cast<float>(total_hr)/static_cast<float>(m_last_hash_rates.size());
        std::cout << "hashrate: " << std::setprecision(4) << std::fixed << hr << ENDL;
      }
    }
    m_last_hr_merge_time = misc_utils::get_tick_count();
    m_hashes = 0;
  }
  //-----------------------------------------------------------------------------------------------------
  void miner::init_options(boost::program_options::options_description& desc)
  {
    command_line::add_arg(desc, arg_extra_messages);
    command_line::add_arg(desc, arg_start_mining);
    command_line::add_arg(desc, arg_mining_threads);
    command_line::add_arg(desc, arg_bg_mining_enable);
    command_line::add_arg(desc, arg_bg_mining_min_idle_interval_seconds);
    command_line::add_arg(desc, arg_bg_mining_idle_threshold_percentage);
    command_line::add_arg(desc, arg_bg_mining_miner_target_percentage);
  }
  //-----------------------------------------------------------------------------------------------------
  bool miner::init(const boost::program_options::variables_map& vm, bool testnet)
  {
    if(command_line::has_arg(vm, arg_extra_messages))
    {
      std::string buff;
      bool r = file_io_utils::load_file_to_string(command_line::get_arg(vm, arg_extra_messages), buff);
      CHECK_AND_ASSERT_MES(r, false, "Failed to load file with extra messages: " << command_line::get_arg(vm, arg_extra_messages));
      std::vector<std::string> extra_vec;
      boost::split(extra_vec, buff, boost::is_any_of("\n"), boost::token_compress_on );
      m_extra_messages.resize(extra_vec.size());
      for(size_t i = 0; i != extra_vec.size(); i++)
      {
        string_tools::trim(extra_vec[i]);
        if(!extra_vec[i].size())
          continue;
        std::string buff = string_encoding::base64_decode(extra_vec[i]);
        if(buff != "0")
          m_extra_messages[i] = buff;
      }
      m_config_folder_path = boost::filesystem::path(command_line::get_arg(vm, arg_extra_messages)).parent_path().string();
      m_config = AUTO_VAL_INIT(m_config);
      epee::serialization::load_t_from_json_file(m_config, m_config_folder_path + "/" + MINER_CONFIG_FILE_NAME);
      MINFO("Loaded " << m_extra_messages.size() << " extra messages, current index " << m_config.current_extra_message_index);
    }

    if(command_line::has_arg(vm, arg_start_mining))
    {
      if(!cryptonote::get_account_address_from_str(m_mine_address, testnet, command_line::get_arg(vm, arg_start_mining)))
      {
        LOG_ERROR("Target account address " << command_line::get_arg(vm, arg_start_mining) << " has wrong format, starting daemon canceled");
        return false;
      }
      m_threads_total = 1;
      m_do_mining = true;
      if(command_line::has_arg(vm, arg_mining_threads))
      {
        m_threads_total = command_line::get_arg(vm, arg_mining_threads);
      }
    }

    // Background mining parameters
    // Let init set all parameters even if background mining is not enabled, they can start later with params set
    if(command_line::has_arg(vm, arg_bg_mining_enable))
      set_is_background_mining_enabled( command_line::get_arg(vm, arg_bg_mining_enable) );
    if(command_line::has_arg(vm, arg_bg_mining_min_idle_interval_seconds))
      set_min_idle_seconds( command_line::get_arg(vm, arg_bg_mining_min_idle_interval_seconds) );
    if(command_line::has_arg(vm, arg_bg_mining_idle_threshold_percentage))
      set_idle_threshold( command_line::get_arg(vm, arg_bg_mining_idle_threshold_percentage) );
    if(command_line::has_arg(vm, arg_bg_mining_miner_target_percentage))
      set_mining_target( command_line::get_arg(vm, arg_bg_mining_miner_target_percentage) );

    return true;
  }
  //-----------------------------------------------------------------------------------------------------
  bool miner::is_mining() const
  {
    return !m_stop;
  }
  //-----------------------------------------------------------------------------------------------------
  const account_public_address& miner::get_mining_address() const
  {
    return m_mine_address;
  }
  //-----------------------------------------------------------------------------------------------------
  uint32_t miner::get_threads_count() const {
    return m_threads_total;
  }
  //-----------------------------------------------------------------------------------------------------
  bool miner::start(const account_public_address& adr, size_t threads_count, const boost::thread::attributes& attrs, bool do_background)
  {
    m_mine_address = adr;
    m_threads_total = static_cast<uint32_t>(threads_count);
    m_starter_nonce = crypto::rand<uint32_t>();
    CRITICAL_REGION_LOCAL(m_threads_lock);
    if(is_mining())
    {
      LOG_ERROR("Starting miner but it's already started");
      return false;
    }

    if(!m_threads.empty())
    {
      LOG_ERROR("Unable to start miner because there are active mining threads");
      return false;
    }

    if(!m_template_no)
      request_block_template();//lets update block template

    boost::interprocess::ipcdetail::atomic_write32(&m_stop, 0);
    boost::interprocess::ipcdetail::atomic_write32(&m_thread_index, 0);

    for(size_t i = 0; i != threads_count; i++)
    {
      m_threads.push_back(boost::thread(attrs, boost::bind(&miner::worker_thread, this)));
    }

    LOG_PRINT_L0("Mining has started with " << threads_count << " threads, good luck!" );

    set_is_background_mining_enabled(do_background);
    if( get_is_background_mining_enabled() )
    {
      m_background_mining_thread = boost::thread(attrs, boost::bind(&miner::background_worker_thread, this));
      LOG_PRINT_L0("Background mining controller thread started" );
    }

    return true;
  }
  //-----------------------------------------------------------------------------------------------------
  uint64_t miner::get_speed() const
  {
    if(is_mining()) {
      return m_current_hash_rate;
    }
    else {
      return 0;
    }
  }
  //-----------------------------------------------------------------------------------------------------
  void miner::send_stop_signal()
  {
    boost::interprocess::ipcdetail::atomic_write32(&m_stop, 1);
  }
  //-----------------------------------------------------------------------------------------------------
  bool miner::stop()
  {
    MTRACE("Miner has received stop signal");

    if (!is_mining())
    {
      MDEBUG("Not mining - nothing to stop" );
      return true;
    }

    send_stop_signal();
    CRITICAL_REGION_LOCAL(m_threads_lock);

    // In case background mining was active and the miner threads are waiting
    // on the background miner to signal start. 
    m_is_background_mining_started_cond.notify_all();

    for(boost::thread& th: m_threads)
      th.join();

    // The background mining thread could be sleeping for a long time, so we
    // interrupt it just in case
    m_background_mining_thread.interrupt();
    m_background_mining_thread.join();

    LOG_PRINT_L0("Mining has been stopped, " << m_threads.size() << " finished" );
    m_threads.clear();
    return true;
  }
  //-----------------------------------------------------------------------------------------------------
  bool miner::find_nonce_for_given_block(block& bl, const difficulty_type& diffic, uint64_t height)
  {
    for(; bl.nonce != std::numeric_limits<uint32_t>::max(); bl.nonce++)
    {
      crypto::hash h;
      get_block_longhash(bl, h, height);

      if(check_hash(h, diffic))
      {
        return true;
      }
    }
    return false;
  }
  //-----------------------------------------------------------------------------------------------------
  void miner::on_synchronized()
  {
    if(m_do_mining)
    {
      boost::thread::attributes attrs;
      attrs.set_stack_size(THREAD_STACK_SIZE);

      start(m_mine_address, m_threads_total, attrs, get_is_background_mining_enabled());
    }
  }
  //-----------------------------------------------------------------------------------------------------
  void miner::pause()
  {
    CRITICAL_REGION_LOCAL(m_miners_count_lock);
    ++m_pausers_count;
    if(m_pausers_count == 1 && is_mining())
      MDEBUG("MINING PAUSED");
  }
  //-----------------------------------------------------------------------------------------------------
  void miner::resume()
  {
    CRITICAL_REGION_LOCAL(m_miners_count_lock);
    --m_pausers_count;
    if(m_pausers_count < 0)
    {
      m_pausers_count = 0;
      MERROR("Unexpected miner::resume() called");
    }
    if(!m_pausers_count && is_mining())
      MDEBUG("MINING RESUMED");
  }
  //-----------------------------------------------------------------------------------------------------
  bool miner::worker_thread()
  {
    uint32_t th_local_index = boost::interprocess::ipcdetail::atomic_inc32(&m_thread_index);
    MGINFO("Miner thread was started ["<< th_local_index << "]");
    MLOG_SET_THREAD_NAME(std::string("[miner ") + std::to_string(th_local_index) + "]");
    uint32_t nonce = m_starter_nonce + th_local_index;
    uint64_t height = 0;
    difficulty_type local_diff = 0;
    uint32_t local_template_ver = 0;
    block b;
    slow_hash_allocate_state();
    while(!m_stop)
    {
      if(m_pausers_count)//anti split workaround
      {
        misc_utils::sleep_no_w(100);
        continue;
      }
      else if( m_is_background_mining_enabled )
      {
        misc_utils::sleep_no_w(m_miner_extra_sleep);
        while( !m_is_background_mining_started )
        {
          MGINFO("background mining is enabled, but not started, waiting until start triggers");
          boost::unique_lock<boost::mutex> started_lock( m_is_background_mining_started_mutex );        
          m_is_background_mining_started_cond.wait( started_lock );
          if( m_stop ) break;
        }
        
        if( m_stop ) continue;         
      }

      if(local_template_ver != m_template_no)
      {
        CRITICAL_REGION_BEGIN(m_template_lock);
        b = m_template;
        local_diff = m_diffic;
        height = m_height;
        CRITICAL_REGION_END();
        local_template_ver = m_template_no;
        nonce = m_starter_nonce + th_local_index;
      }

      if(!local_template_ver)//no any set_block_template call
      {
        LOG_PRINT_L2("Block template not set yet");
        epee::misc_utils::sleep_no_w(1000);
        continue;
      }

      b.nonce = nonce;
      crypto::hash h;
      get_block_longhash(b, h, height);

      if(check_hash(h, local_diff))
      {
        //we lucky!
        ++m_config.current_extra_message_index;
        MGINFO_GREEN("Found block for difficulty: " << local_diff);
        if(!m_phandler->handle_block_found(b))
        {
          --m_config.current_extra_message_index;
        }else
        {
          //success update, lets update config
          if (!m_config_folder_path.empty())
            epee::serialization::store_t_to_json_file(m_config, m_config_folder_path + "/" + MINER_CONFIG_FILE_NAME);
        }
      }
      nonce+=m_threads_total;
      ++m_hashes;
    }
    slow_hash_free_state();
    MGINFO("Miner thread stopped ["<< th_local_index << "]");
    return true;
  }
  //-----------------------------------------------------------------------------------------------------
  bool miner::get_is_background_mining_enabled() const
  {
    return m_is_background_mining_enabled;
  }
  //-----------------------------------------------------------------------------------------------------
  /**
  * This has differing behaviour depending on if mining has been started/etc.
  * Note: add documentation
  */
  bool miner::set_is_background_mining_enabled(bool is_background_mining_enabled)
  {
    m_is_background_mining_enabled = is_background_mining_enabled;
    // Extra logic will be required if we make this function public in the future
    // and allow toggling smart mining without start/stop
    //m_is_background_mining_enabled_cond.notify_one();
    return true;
  }
  //-----------------------------------------------------------------------------------------------------
  uint64_t miner::get_min_idle_seconds() const
  {
    return m_min_idle_seconds;
  }
  //-----------------------------------------------------------------------------------------------------
  bool miner::set_min_idle_seconds(uint64_t min_idle_seconds)
  {
    if(min_idle_seconds > BACKGROUND_MINING_MAX_MIN_IDLE_INTERVAL_IN_SECONDS) return false;
    if(min_idle_seconds < BACKGROUND_MINING_MIN_MIN_IDLE_INTERVAL_IN_SECONDS) return false;
    m_min_idle_seconds = min_idle_seconds;
    return true;
  }
  //-----------------------------------------------------------------------------------------------------
  uint8_t miner::get_idle_threshold() const
  {
    return m_idle_threshold;
  }
  //-----------------------------------------------------------------------------------------------------
  bool miner::set_idle_threshold(uint8_t idle_threshold)
  {
    if(idle_threshold > BACKGROUND_MINING_MAX_IDLE_THRESHOLD_PERCENTAGE) return false;
    if(idle_threshold < BACKGROUND_MINING_MIN_IDLE_THRESHOLD_PERCENTAGE) return false;
    m_idle_threshold = idle_threshold;
    return true;
  }
  //-----------------------------------------------------------------------------------------------------
  uint8_t miner::get_mining_target() const
  {
    return m_mining_target;
  }
  //-----------------------------------------------------------------------------------------------------
  bool miner::set_mining_target(uint8_t mining_target)
  {
    if(mining_target > BACKGROUND_MINING_MAX_MINING_TARGET_PERCENTAGE) return false;
    if(mining_target < BACKGROUND_MINING_MIN_MINING_TARGET_PERCENTAGE) return false;
    m_mining_target = mining_target;
    return true;
  }
  //-----------------------------------------------------------------------------------------------------
  bool miner::background_worker_thread()
  {
    uint64_t prev_total_time, current_total_time;
    uint64_t prev_idle_time, current_idle_time;
    uint64_t previous_process_time = 0, current_process_time = 0;
    m_is_background_mining_enabled = false;

    if(!get_system_times(prev_total_time, prev_idle_time))
    {
      LOG_ERROR(__func__ << " : get_system_times call failed, background mining will NOT work!");
      return false;
    }
    
    while(!m_stop)
    {
        
      try
      {
        // Commenting out the below since we're going with privatizing the bg mining enabled
        // function, but I'll leave the code/comments here for anyone that wants to modify the
        // patch in the future
        // -------------------------------------------------------------------------------------
        // All of this might be overkill if we just enforced some simple requirements
        // about changing this variable before/after the miner starts, but I envision
        // in the future a checkbox that you can tick on/off for background mining after
        // you've clicked "start mining". There's still an issue here where if background
        // mining is disabled when start is called, this thread is never created, and so
        // enabling after does nothing, something I have to fix in the future. However,
        // this should take care of the case where mining is started with bg-enabled, 
        // and then the user decides to un-check background mining, and just do
        // regular full-speed mining. I might just be over-doing it and thinking up 
        // non-existant use-cases, so if the concensus is to simplify, we can remove all this fluff.
        /*
        while( !m_is_background_mining_enabled )
        {
          MGINFO(__func__ << " : background mining is disabled, waiting until enabled!");
          boost::unique_lock<boost::mutex> enabled_lock( m_is_background_mining_enabled_mutex );        
          m_is_background_mining_enabled_cond.wait( enabled_lock );
        } 
        */       
        
        // If we're already mining, then sleep for the miner monitor interval.
        // If we're NOT mining, then sleep for the idle monitor interval
        boost::this_thread::sleep_for( 
          m_is_background_mining_started ? 
            boost::chrono::seconds( BACKGROUND_MINING_MINER_MONITOR_INVERVAL_IN_SECONDS ) :
            boost::chrono::seconds( get_min_idle_seconds() ) );
      }
      catch(boost::thread_interrupted)
      {
        MGINFO(__func__ << " : background miner thread interrupted ");
        continue; // if interrupted because stop called, loop should end ..
      }
      
      if( m_is_background_mining_started )
      {
        // figure out if we need to stop, and monitor mining usage
        
        // If we get here, then previous values are initialized.
        // Let's get some current data for comparison.

        if(!get_system_times(current_total_time, current_idle_time))
        {
          LOG_ERROR(__func__ << " : get_system_times call failed");
          continue;
        }

        if(!get_process_time(current_process_time))
        {
          LOG_ERROR(__func__ << " : get_process_time call failed!");
          continue;
        }

        uint64_t total_diff = (current_total_time - prev_total_time);
        uint64_t idle_diff = (current_idle_time - prev_idle_time);
        uint64_t process_diff = (current_process_time - previous_process_time);
        uint8_t idle_percentage = get_percent_of_total(idle_diff, total_diff);
        uint8_t process_percentage = get_percent_of_total(process_diff, total_diff);
        bool on_ac_power = ac_line_status();
        MGINFO(__func__ << " : idle percentage is " << unsigned(idle_percentage) << "\%, miner percentage is " << unsigned(process_percentage) << "\%, ac power : " << on_ac_power);
        if( idle_percentage + process_percentage < get_idle_threshold() || !ac_line_status() )
        {
          MGINFO(__func__ << " : cpu is " << unsigned(idle_percentage) << "% idle, idle threshold is " << unsigned(get_idle_threshold()) << "\%, ac power : " << on_ac_power << ", background mining stopping, thanks for your contribution!");
          m_is_background_mining_started = false;

          // reset process times
          previous_process_time = 0;
          current_process_time = 0;
        }
        else
        {
          previous_process_time = current_process_time;

          // adjust the miner extra sleep variable
          int64_t miner_extra_sleep_change = (-1 * (get_mining_target() - process_percentage) );
          int64_t new_miner_extra_sleep = m_miner_extra_sleep + miner_extra_sleep_change;
          // if you start the miner with few threads on a multicore system, this could
          // fall below zero because all the time functions aggregate across all processors.
          // I'm just hard limiting to 5 millis min sleep here, other options?
          m_miner_extra_sleep = std::max( new_miner_extra_sleep , (int64_t)5 );
          MGINFO(__func__ << " : m_miner_extra_sleep " << m_miner_extra_sleep);
        }
        
        prev_total_time = current_total_time;
        prev_idle_time = current_idle_time;
      }
      else
      {
        // figure out if we need to start

        if(!get_system_times(current_total_time, current_idle_time))
        {
          LOG_ERROR(__func__ << " : get_system_times call failed");
          continue;
        }

        uint64_t total_diff = (current_total_time - prev_total_time);
        uint64_t idle_diff = (current_idle_time - prev_idle_time);
        uint8_t idle_percentage = get_percent_of_total(idle_diff, total_diff);
        bool on_ac_power = ac_line_status();
        MGINFO(__func__ << " : idle percentage is " << unsigned(idle_percentage));
        if( idle_percentage >= get_idle_threshold() && on_ac_power )
        {
          MGINFO(__func__ << " : cpu is " << unsigned(idle_percentage) << "% idle, idle threshold is " << unsigned(get_idle_threshold()) << "\%, ac power : " << on_ac_power << ", background mining started, good luck!");
          m_is_background_mining_started = true;
          m_is_background_mining_started_cond.notify_all();

          // Wait for a little mining to happen ..
          boost::this_thread::sleep_for(boost::chrono::seconds( 1 ));

          // Starting data ...
          if(!get_process_time(previous_process_time))
          {
            m_is_background_mining_started = false;
            LOG_ERROR(__func__ << " : get_process_time call failed!");
          }
        }

        prev_total_time = current_total_time;
        prev_idle_time = current_idle_time;
      }
    }

    return true;
  }
  //-----------------------------------------------------------------------------------------------------
  bool miner::get_system_times(uint64_t& total_time, uint64_t& idle_time)
  {
    #ifdef _WIN32

    	FILETIME idleTime;
    	FILETIME kernelTime;
    	FILETIME userTime;
    	if ( GetSystemTimes( &idleTime, &kernelTime, &userTime ) != -1 )
    	{
        total_time =
          ( (((uint64_t)(kernelTime.dwHighDateTime)) << 32) | ((uint64_t)kernelTime.dwLowDateTime) )
          + ( (((uint64_t)(userTime.dwHighDateTime)) << 32) | ((uint64_t)userTime.dwLowDateTime) );

        idle_time = ( (((uint64_t)(idleTime.dwHighDateTime)) << 32) | ((uint64_t)idleTime.dwLowDateTime) );

        return true;
    	}

    #elif defined(__linux__)

      const std::string STR_CPU("cpu");
      const std::size_t STR_CPU_LEN = STR_CPU.size();
      const std::string STAT_FILE_PATH = "/proc/stat";

      if( !epee::file_io_utils::is_file_exist(STAT_FILE_PATH) )
      {
        LOG_ERROR(__func__ << " : '" << STAT_FILE_PATH << "' file does not exist");
        return false;
      }

      std::ifstream stat_file_stream(STAT_FILE_PATH);
      if( stat_file_stream.fail() )
      {
        LOG_ERROR(__func__ << " : failed to open '" << STAT_FILE_PATH << "'");
        return false;
      }

      std::string line;
      std::getline(stat_file_stream, line);
      std::istringstream stat_file_iss(line);
      stat_file_iss.ignore(65536, ' '); // skip cpu label ...
      uint64_t utime, ntime, stime, itime;
      if( !(stat_file_iss >> utime && stat_file_iss >> ntime && stat_file_iss >> stime && stat_file_iss >> itime) )
      {
        LOG_ERROR(__func__ << " : failed to read '" << STAT_FILE_PATH << "'");
        return false;
      }

      idle_time = itime;
      total_time = utime + ntime + stime + itime;

      return true;

    #endif

    return false; // unsupported systemm..
  }
  //-----------------------------------------------------------------------------------------------------
  bool miner::get_process_time(uint64_t& total_time)
  {
    #ifdef _WIN32

      FILETIME createTime;
      FILETIME exitTime;
      FILETIME kernelTime;
      FILETIME userTime;
      if ( GetProcessTimes( GetCurrentProcess(), &createTime, &exitTime, &kernelTime, &userTime ) != -1 )
      {
        total_time =
          ( (((uint64_t)(kernelTime.dwHighDateTime)) << 32) | ((uint64_t)kernelTime.dwLowDateTime) )
          + ( (((uint64_t)(userTime.dwHighDateTime)) << 32) | ((uint64_t)userTime.dwLowDateTime) );

        return true;
      }

    #elif defined(__linux__) && defined(_SC_CLK_TCK)

      struct tms tms;
      if ( times(&tms) != (clock_t)-1 )
      {
    		total_time = tms.tms_utime + tms.tms_stime;
        return true;
      }

    #endif

    return false; // unsupported system..
  }
  //-----------------------------------------------------------------------------------------------------  
  uint8_t miner::get_percent_of_total(uint64_t other, uint64_t total)
  {
    return (uint8_t)( ceil( (other * 1.f / total * 1.f) * 100) );    
  }
  //-----------------------------------------------------------------------------------------------------    
  bool miner::ac_line_status()
  {
    #ifdef _WIN32

      SYSTEM_POWER_STATUS power_status;
    	if ( GetSystemPowerStatus( &power_status ) != 0 )
    	{
        return power_status.ACLineStatus == 1;
    	}

    #elif defined(__linux__)

      // i've only tested on UBUNTU, these paths might be different on other systems
      // need to figure out a way to make this more flexible
      const std::string POWER_SUPPLY_STATUS_PATH = "/sys/class/power_supply/ACAD/online";

      if( !epee::file_io_utils::is_file_exist(POWER_SUPPLY_STATUS_PATH) )
      {
        LOG_ERROR(__func__ << " : '" << POWER_SUPPLY_STATUS_PATH << "' file does not exist, can't determine if on AC power");
        return false;
      }

      std::ifstream power_stream(POWER_SUPPLY_STATUS_PATH);
      if( power_stream.fail() )
      {
        LOG_ERROR(__func__ << " : failed to open '" << POWER_SUPPLY_STATUS_PATH << "'");
        return false;
      }

      return power_stream.get() == '1';

    #endif
    
    LOG_ERROR(__func__ << " : couldn't query power status");
    return false; // shouldn't get here unless no support for querying battery status
  }
}