parallel_for.h

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// ======================================================================== //
// Copyright 2018-2019 Ingo Wald                                            //
//                                                                          //
// Licensed 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.                                           //
// ======================================================================== //
 
#pragma once
 
#include <owl/common/owl-common.h>
// std
#include <mutex>
 
#ifdef OWL_DISABLE_TBB
# undef OWL_HAVE_TBB
#endif
 
// tbb
#if OWL_HAVE_TBB
#include <tbb/parallel_for.h>
#include <tbb/task_arena.h>
#define OWL_HAVE_PARALLEL_FOR 1
#endif
 
namespace owl {
  namespace common {
 
    template<typename INDEX_T, typename TASK_T>
    inline void serial_for(INDEX_T nTasks, TASK_T&& taskFunction)
    {
      for (INDEX_T taskIndex = 0; taskIndex < nTasks; ++taskIndex) {
        taskFunction(taskIndex);
      }
    }
  
#if OWL_HAVE_TBB
    template<typename INDEX_T, typename TASK_T>
    inline void parallel_for(INDEX_T nTasks, TASK_T&& taskFunction, size_t blockSize=1)
    {
      if (nTasks == 0) return;
      if (nTasks == 1)
        taskFunction(size_t(0));
      else if (blockSize==1) {
        tbb::parallel_for(INDEX_T(0), nTasks, std::forward<TASK_T>(taskFunction));
      } else {
        const size_t numBlocks = (nTasks+blockSize-1)/blockSize;
        tbb::parallel_for((size_t)0, numBlocks, [&](size_t blockIdx){
            size_t begin = blockIdx*blockSize;
            size_t end   = std::min(begin+blockSize,size_t(nTasks));
            for (size_t i=begin;i<end;i++)
              taskFunction(INDEX_T(i));
          });
      }
    }
#else
#ifndef OWL_DISABLE_TBB
# pragma message("warning: TBB not available, will replace all parallel_for's with serial_for's")
#endif
    template<typename INDEX_T, typename TASK_T>
    inline void parallel_for(INDEX_T nTasks, TASK_T&& taskFunction, size_t blockSize=1)
    { serial_for(nTasks,taskFunction); }
#endif
  
    // template<typename TASK_T>
    // void parallel_for_blocked(size_t numTasks, size_t blockSize,
    //                           TASK_T &&taskFunction)
    // {
    //   for (size_t begin=0; begin < numTasks; begin += blockSize)
    //     taskFunction(begin,std::min(begin+blockSize,numTasks));
    // }
 
    template<typename TASK_T>
    void serial_for_blocked(size_t begin, size_t end, size_t blockSize,
                            TASK_T &&taskFunction)
    {
      for (size_t block_begin=begin; block_begin < end; block_begin += blockSize)
        taskFunction(block_begin,std::min(block_begin+blockSize,end));
    }
  
    template<typename TASK_T>
    void parallel_for_blocked(size_t begin, size_t end, size_t blockSize,
                              const TASK_T &taskFunction)
    {
#if 0
      serial_for_blocked(begin,end,blockSize,taskFunction);
#else
      const size_t numTasks = end-begin;
      const size_t numBlocks = (numTasks+blockSize-1)/blockSize;
      parallel_for(numBlocks,[&](size_t blockID){
          size_t block_begin = begin+blockID*blockSize;
          taskFunction(block_begin,std::min(block_begin+blockSize,end));
        });
#endif
    }
  
  } // ::owl::common
} // ::owl