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       1                 :            : // Copyright (c) 2012-2022 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 <sync.h>
       9                 :            : #include <tinyformat.h>
      10                 :            : #include <util/threadnames.h>
      11                 :            : 
      12                 :            : #include <algorithm>
      13                 :            : #include <iterator>
      14                 :            : #include <vector>
      15                 :            : 
      16                 :            : /**
      17                 :            :  * Queue for verifications that have to be performed.
      18                 :            :   * The verifications are represented by a type T, which must provide an
      19                 :            :   * operator(), returning a bool.
      20                 :            :   *
      21                 :            :   * One thread (the master) is assumed to push batches of verifications
      22                 :            :   * onto the queue, where they are processed by N-1 worker threads. When
      23                 :            :   * the master is done adding work, it temporarily joins the worker pool
      24                 :            :   * as an N'th worker, until all jobs are done.
      25                 :            :   */
      26                 :            : template <typename T>
      27                 :            : class CCheckQueue
      28                 :            : {
      29                 :            : private:
      30                 :            :     //! Mutex to protect the inner state
      31                 :            :     Mutex m_mutex;
      32                 :            : 
      33                 :            :     //! Worker threads block on this when out of work
      34                 :            :     std::condition_variable m_worker_cv;
      35                 :            : 
      36                 :            :     //! Master thread blocks on this when out of work
      37                 :            :     std::condition_variable m_master_cv;
      38                 :            : 
      39                 :            :     //! The queue of elements to be processed.
      40                 :            :     //! As the order of booleans doesn't matter, it is used as a LIFO (stack)
      41                 :            :     std::vector<T> queue GUARDED_BY(m_mutex);
      42                 :            : 
      43                 :            :     //! The number of workers (including the master) that are idle.
      44                 :          0 :     int nIdle GUARDED_BY(m_mutex){0};
      45                 :            : 
      46                 :            :     //! The total number of workers (including the master).
      47                 :          0 :     int nTotal GUARDED_BY(m_mutex){0};
      48                 :            : 
      49                 :            :     //! The temporary evaluation result.
      50                 :          0 :     bool fAllOk GUARDED_BY(m_mutex){true};
      51                 :            : 
      52                 :            :     /**
      53                 :            :      * Number of verifications that haven't completed yet.
      54                 :            :      * This includes elements that are no longer queued, but still in the
      55                 :            :      * worker's own batches.
      56                 :            :      */
      57                 :          0 :     unsigned int nTodo GUARDED_BY(m_mutex){0};
      58                 :            : 
      59                 :            :     //! The maximum number of elements to be processed in one batch
      60                 :            :     const unsigned int nBatchSize;
      61                 :            : 
      62                 :            :     std::vector<std::thread> m_worker_threads;
      63                 :          0 :     bool m_request_stop GUARDED_BY(m_mutex){false};
      64                 :            : 
      65                 :            :     /** Internal function that does bulk of the verification work. */
      66                 :          0 :     bool Loop(bool fMaster) EXCLUSIVE_LOCKS_REQUIRED(!m_mutex)
      67                 :            :     {
      68         [ #  # ]:          0 :         std::condition_variable& cond = fMaster ? m_master_cv : m_worker_cv;
      69                 :          0 :         std::vector<T> vChecks;
      70         [ #  # ]:          0 :         vChecks.reserve(nBatchSize);
      71                 :          0 :         unsigned int nNow = 0;
      72                 :          0 :         bool fOk = true;
      73                 :          0 :         do {
      74                 :            :             {
      75 [ #  # ][ #  # ]:          0 :                 WAIT_LOCK(m_mutex, lock);
      76                 :            :                 // first do the clean-up of the previous loop run (allowing us to do it in the same critsect)
      77         [ #  # ]:          0 :                 if (nNow) {
      78                 :          0 :                     fAllOk &= fOk;
      79                 :          0 :                     nTodo -= nNow;
      80 [ #  # ][ #  # ]:          0 :                     if (nTodo == 0 && !fMaster)
      81                 :            :                         // We processed the last element; inform the master it can exit and return the result
      82                 :          0 :                         m_master_cv.notify_one();
      83                 :          0 :                 } else {
      84                 :            :                     // first iteration
      85                 :          0 :                     nTotal++;
      86                 :            :                 }
      87                 :            :                 // logically, the do loop starts here
      88 [ #  # ][ #  # ]:          0 :                 while (queue.empty() && !m_request_stop) {
      89 [ #  # ][ #  # ]:          0 :                     if (fMaster && nTodo == 0) {
      90                 :          0 :                         nTotal--;
      91                 :          0 :                         bool fRet = fAllOk;
      92                 :            :                         // reset the status for new work later
      93                 :          0 :                         fAllOk = true;
      94                 :            :                         // return the current status
      95                 :          0 :                         return fRet;
      96                 :            :                     }
      97                 :          0 :                     nIdle++;
      98         [ #  # ]:          0 :                     cond.wait(lock); // wait
      99                 :          0 :                     nIdle--;
     100                 :            :                 }
     101         [ #  # ]:          0 :                 if (m_request_stop) {
     102                 :          0 :                     return false;
     103                 :            :                 }
     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 [ #  # ][ #  # ]:          0 :                 nNow = std::max(1U, std::min(nBatchSize, (unsigned int)queue.size() / (nTotal + nIdle + 1)));
     111                 :          0 :                 auto start_it = queue.end() - nNow;
     112 [ #  # ][ #  # ]:          0 :                 vChecks.assign(std::make_move_iterator(start_it), std::make_move_iterator(queue.end()));
                 [ #  # ]
     113         [ #  # ]:          0 :                 queue.erase(start_it, queue.end());
     114                 :            :                 // Check whether we need to do work at all
     115                 :          0 :                 fOk = fAllOk;
     116         [ #  # ]:          0 :             }
     117                 :            :             // execute work
     118         [ #  # ]:          0 :             for (T& check : vChecks)
     119         [ #  # ]:          0 :                 if (fOk)
     120         [ #  # ]:          0 :                     fOk = check();
     121                 :          0 :             vChecks.clear();
     122         [ #  # ]:          0 :         } while (true);
     123                 :          0 :     }
     124                 :            : 
     125                 :            : public:
     126                 :            :     //! Mutex to ensure only one concurrent CCheckQueueControl
     127                 :            :     Mutex m_control_mutex;
     128                 :            : 
     129                 :            :     //! Create a new check queue
     130                 :          0 :     explicit CCheckQueue(unsigned int batch_size, int worker_threads_num)
     131                 :          0 :         : nBatchSize(batch_size)
     132                 :            :     {
     133         [ #  # ]:          0 :         m_worker_threads.reserve(worker_threads_num);
     134         [ #  # ]:          0 :         for (int n = 0; n < worker_threads_num; ++n) {
     135         [ #  # ]:          0 :             m_worker_threads.emplace_back([this, n]() {
     136         [ #  # ]:          0 :                 util::ThreadRename(strprintf("scriptch.%i", n));
     137                 :          0 :                 Loop(false /* worker thread */);
     138                 :          0 :             });
     139                 :          0 :         }
     140                 :          0 :     }
     141                 :            : 
     142                 :            :     // Since this class manages its own resources, which is a thread
     143                 :            :     // pool `m_worker_threads`, copy and move operations are not appropriate.
     144                 :            :     CCheckQueue(const CCheckQueue&) = delete;
     145                 :            :     CCheckQueue& operator=(const CCheckQueue&) = delete;
     146                 :            :     CCheckQueue(CCheckQueue&&) = delete;
     147                 :            :     CCheckQueue& operator=(CCheckQueue&&) = delete;
     148                 :            : 
     149                 :            :     //! Wait until execution finishes, and return whether all evaluations were successful.
     150                 :          0 :     bool Wait() EXCLUSIVE_LOCKS_REQUIRED(!m_mutex)
     151                 :            :     {
     152                 :          0 :         return Loop(true /* master thread */);
     153                 :            :     }
     154                 :            : 
     155                 :            :     //! Add a batch of checks to the queue
     156                 :          0 :     void Add(std::vector<T>&& vChecks) EXCLUSIVE_LOCKS_REQUIRED(!m_mutex)
     157                 :            :     {
     158         [ #  # ]:          0 :         if (vChecks.empty()) {
     159                 :          0 :             return;
     160                 :            :         }
     161                 :            : 
     162                 :            :         {
     163                 :          0 :             LOCK(m_mutex);
     164 [ #  # ][ #  # ]:          0 :             queue.insert(queue.end(), std::make_move_iterator(vChecks.begin()), std::make_move_iterator(vChecks.end()));
                 [ #  # ]
     165                 :          0 :             nTodo += vChecks.size();
     166                 :          0 :         }
     167                 :            : 
     168         [ #  # ]:          0 :         if (vChecks.size() == 1) {
     169                 :          0 :             m_worker_cv.notify_one();
     170                 :          0 :         } else {
     171                 :          0 :             m_worker_cv.notify_all();
     172                 :            :         }
     173                 :          0 :     }
     174                 :            : 
     175                 :          0 :     ~CCheckQueue()
     176                 :            :     {
     177         [ #  # ]:          0 :         WITH_LOCK(m_mutex, m_request_stop = true);
     178                 :          0 :         m_worker_cv.notify_all();
     179         [ #  # ]:          0 :         for (std::thread& t : m_worker_threads) {
     180         [ #  # ]:          0 :             t.join();
     181                 :            :         }
     182                 :          0 :     }
     183                 :            : 
     184                 :          0 :     bool HasThreads() const { return !m_worker_threads.empty(); }
     185                 :            : };
     186                 :            : 
     187                 :            : /**
     188                 :            :  * RAII-style controller object for a CCheckQueue that guarantees the passed
     189                 :            :  * queue is finished before continuing.
     190                 :            :  */
     191                 :            : template <typename T>
     192                 :            : class CCheckQueueControl
     193                 :            : {
     194                 :            : private:
     195                 :            :     CCheckQueue<T> * const pqueue;
     196                 :            :     bool fDone;
     197                 :            : 
     198                 :            : public:
     199                 :            :     CCheckQueueControl() = delete;
     200                 :            :     CCheckQueueControl(const CCheckQueueControl&) = delete;
     201                 :            :     CCheckQueueControl& operator=(const CCheckQueueControl&) = delete;
     202                 :          0 :     explicit CCheckQueueControl(CCheckQueue<T> * const pqueueIn) : pqueue(pqueueIn), fDone(false)
     203                 :            :     {
     204                 :            :         // passed queue is supposed to be unused, or nullptr
     205         [ #  # ]:          0 :         if (pqueue != nullptr) {
     206                 :          0 :             ENTER_CRITICAL_SECTION(pqueue->m_control_mutex);
     207                 :          0 :         }
     208                 :          0 :     }
     209                 :            : 
     210                 :          0 :     bool Wait()
     211                 :            :     {
     212         [ #  # ]:          0 :         if (pqueue == nullptr)
     213                 :          0 :             return true;
     214                 :          0 :         bool fRet = pqueue->Wait();
     215                 :          0 :         fDone = true;
     216                 :          0 :         return fRet;
     217                 :          0 :     }
     218                 :            : 
     219                 :          0 :     void Add(std::vector<T>&& vChecks)
     220                 :            :     {
     221         [ #  # ]:          0 :         if (pqueue != nullptr) {
     222                 :          0 :             pqueue->Add(std::move(vChecks));
     223                 :          0 :         }
     224                 :          0 :     }
     225                 :            : 
     226                 :          0 :     ~CCheckQueueControl()
     227                 :            :     {
     228         [ #  # ]:          0 :         if (!fDone)
     229         [ #  # ]:          0 :             Wait();
     230         [ #  # ]:          0 :         if (pqueue != nullptr) {
     231 [ #  # ][ #  # ]:          0 :             LEAVE_CRITICAL_SECTION(pqueue->m_control_mutex);
     232                 :          0 :         }
     233                 :          0 :     }
     234                 :            : };
     235                 :            : 
     236                 :            : #endif // BITCOIN_CHECKQUEUE_H