src/checkqueue.h

   1 // Copyright (c) 2012-2015 The Bitcoin Core developers
   2 // Distributed under the MIT software license, see the accompanying
   3 // file COPYING or http://www.opensource.org/licenses/mit-license.php.
   4
   5 #ifndef BITCOIN_CHECKQUEUE_H
   6 #define BITCOIN_CHECKQUEUE_H
   7
   8 #include <algorithm>
   9 #include <vector>
  10
  11 #include <boost/foreach.hpp>
  12 #include <boost/thread/condition_variable.hpp>
  13 #include <boost/thread/locks.hpp>
  14 #include <boost/thread/mutex.hpp>
  15
  16 template <typename T>
  17 class CCheckQueueControl;
  18
  19 /**
  20  * Queue for verifications that have to be performed.
  21   * The verifications are represented by a type T, which must provide an
  22   * operator(), returning a bool.
  23   *
  24   * One thread (the master) is assumed to push batches of verifications
  25   * onto the queue, where they are processed by N-1 worker threads. When
  26   * the master is done adding work, it temporarily joins the worker pool
  27   * as an N'th worker, until all jobs are done.
  28   */
  29 template <typename T>
  30 class CCheckQueue
  31 {
  32 private:
  33     //! Mutex to protect the inner state
  34     boost::mutex mutex;
  35
  36     //! Worker threads block on this when out of work
  37     boost::condition_variable condWorker;
  38
  39     //! Master thread blocks on this when out of work
  40     boost::condition_variable condMaster;
  41
  42     //! The queue of elements to be processed.
  43     //! As the order of booleans doesn't matter, it is used as a LIFO (stack)
  44     std::vector<T> queue;
  45
  46     //! The number of workers (including the master) that are idle.
  47     int nIdle;
  48
  49     //! The total number of workers (including the master).
  50     int nTotal;
  51
  52     //! The temporary evaluation result.
  53     bool fAllOk;
  54
  55     /**
  56      * Number of verifications that haven't completed yet.
  57      * This includes elements that are no longer queued, but still in the
  58      * worker's own batches.
  59      */
  60     unsigned int nTodo;
  61
  62     //! Whether we're shutting down.
  63     bool fQuit;
  64
  65     //! The maximum number of elements to be processed in one batch
  66     unsigned int nBatchSize;
  67
  68     /** Internal function that does bulk of the verification work. */
  69     bool Loop(bool fMaster = false)
  70     {
  71         boost::condition_variable& cond = fMaster ? condMaster : condWorker;
  72         std::vector<T> vChecks;
  73         vChecks.reserve(nBatchSize);
  74         unsigned int nNow = 0;
  75         bool fOk = true;
  76         do {
  77             {
  78                 boost::unique_lock<boost::mutex> lock(mutex);
  79                 // first do the clean-up of the previous loop run (allowing us to do it in the same critsect)
  80                 if (nNow) {
  81                     fAllOk &= fOk;
  82                     nTodo -= nNow;
  83                     if (nTodo == 0 && !fMaster)
  84                         // We processed the last element; inform the master it can exit and return the result
  85                         condMaster.notify_one();
  86                 } else {
  87                     // first iteration
  88                     nTotal++;
  89                 }
  90                 // logically, the do loop starts here
  91                 while (queue.empty()) {
  92                     if ((fMaster || fQuit) && nTodo == 0) {
  93                         nTotal--;
  94                         bool fRet = fAllOk;
  95                         // reset the status for new work later
  96                         if (fMaster)
  97                             fAllOk = true;
  98                         // return the current status
  99                         return fRet;
 100                     }
 101                     nIdle++;
 102                     cond.wait(lock); // wait
 103                     nIdle--;
 104                 }
 105                 // Decide how many work units to process now.
 106                 // * Do not try to do everything at once, but aim for increasingly smaller batches so
 107                 //   all workers finish approximately simultaneously.
 108                 // * Try to account for idle jobs which will instantly start helping.
 109                 // * Don't do batches smaller than 1 (duh), or larger than nBatchSize.
 110                 nNow = std::max(1U, std::min(nBatchSize, (unsigned int)queue.size() / (nTotal + nIdle + 1)));
 111                 vChecks.resize(nNow);
 112                 for (unsigned int i = 0; i < nNow; i++) {
 113                     // We want the lock on the mutex to be as short as possible, so swap jobs from the global
 114                     // queue to the local batch vector instead of copying.
 115                     vChecks[i].swap(queue.back());
 116                     queue.pop_back();
 117                 }
 118                 // Check whether we need to do work at all
 119                 fOk = fAllOk;
 120             }
 121             // execute work
 122             BOOST_FOREACH (T& check, vChecks)
 123                 if (fOk)
 124                     fOk = check();
 125             vChecks.clear();
 126         } while (true);
 127     }
 128
 129 public:
 130     //! Create a new check queue
 131     CCheckQueue(unsigned int nBatchSizeIn) : nIdle(0), nTotal(0), fAllOk(true), nTodo(0), fQuit(false), nBatchSize(nBatchSizeIn) {}
 132
 133     //! Worker thread
 134     void Thread()
 135     {
 136         Loop();
 137     }
 138
 139     //! Wait until execution finishes, and return whether all evaluations were successful.
 140     bool Wait()
 141     {
 142         return Loop(true);
 143     }
 144
 145     //! Add a batch of checks to the queue
 146     void Add(std::vector<T>& vChecks)
 147     {
 148         boost::unique_lock<boost::mutex> lock(mutex);
 149         BOOST_FOREACH (T& check, vChecks) {
 150             queue.push_back(T());
 151             check.swap(queue.back());
 152         }
 153         nTodo += vChecks.size();
 154         if (vChecks.size() == 1)
 155             condWorker.notify_one();
 156         else if (vChecks.size() > 1)
 157             condWorker.notify_all();
 158     }
 159
 160     ~CCheckQueue()
 161     {
 162     }
 163
 164     bool IsIdle()
 165     {
 166         boost::unique_lock<boost::mutex> lock(mutex);
 167         return (nTotal == nIdle && nTodo == 0 && fAllOk == true);
 168     }
 169
 170 };
 171
 172 /**
 173  * RAII-style controller object for a CCheckQueue that guarantees the passed
 174  * queue is finished before continuing.
 175  */
 176 template <typename T>
 177 class CCheckQueueControl
 178 {
 179 private:
 180     CCheckQueue<T>* pqueue;
 181     bool fDone;
 182
 183 public:
 184     CCheckQueueControl(CCheckQueue<T>* pqueueIn) : pqueue(pqueueIn), fDone(false)
 185     {
 186         // passed queue is supposed to be unused, or NULL
 187         if (pqueue != NULL) {
 188             bool isIdle = pqueue->IsIdle();
 189             assert(isIdle);
 190         }
 191     }
 192
 193     bool Wait()
 194     {
 195         if (pqueue == NULL)
 196             return true;
 197         bool fRet = pqueue->Wait();
 198         fDone = true;
 199         return fRet;
 200     }
 201
 202     void Add(std::vector<T>& vChecks)
 203     {
 204         if (pqueue != NULL)
 205             pqueue->Add(vChecks);
 206     }
 207
 208     ~CCheckQueueControl()
 209     {
 210         if (!fDone)
 211             Wait();
 212     }
 213 };
 214
 215 #endif // BITCOIN_CHECKQUEUE_H