parallel_map.h

// Copyright 2009-2021 Intel Corporation
// SPDX-License-Identifier: Apache-2.0

#pragma once

#include "parallel_sort.h"

namespace embree
{
  /*! implementation of a key/value map with parallel construction */
  template<typename Key, typename Val>
  class parallel_map
  {
    /* key/value pair to build the map */
    struct KeyValue
    {
      __forceinline KeyValue () {}

      __forceinline KeyValue (const Key key, const Val val)
	: key(key), val(val) {}

      __forceinline operator Key() const {
	return key;
      }

    public:
      Key key;
      Val val;
    };

  public:
    
    /*! parallel map constructors */
    parallel_map () {}

    /*! construction from pair of vectors */
    template<typename KeyVector, typename ValVector>
      parallel_map (const KeyVector& keys, const ValVector& values) { init(keys,values); }

    /*! initialized the parallel map from a vector with keys and values */
    template<typename KeyVector, typename ValVector>
      void init(const KeyVector& keys, const ValVector& values) 
    {
      /* reserve sufficient space for all data */
      assert(keys.size() == values.size());
      vec.resize(keys.size());
      
      /* generate key/value pairs */
      parallel_for( size_t(0), keys.size(), size_t(4*4096), [&](const range<size_t>& r) {
	for (size_t i=r.begin(); i<r.end(); i++)
	  vec[i] = KeyValue((Key)keys[i],values[i]);
      });

      /* perform parallel radix sort of the key/value pairs */
      std::vector<KeyValue> temp(keys.size());
      radix_sort<KeyValue,Key>(vec.data(),temp.data(),keys.size());
    }

    /*! Returns a pointer to the value associated with the specified key. The pointer will be nullptr of the key is not contained in the map. */
    __forceinline const Val* lookup(const Key& key) const 
    {
      typename std::vector<KeyValue>::const_iterator i = std::lower_bound(vec.begin(), vec.end(), key);
      if (i == vec.end()) return nullptr;
      if (i->key != key) return nullptr;
      return &i->val;
    }

    /*! If the key is in the map, the function returns the value associated with the key, otherwise it returns the default value. */
    __forceinline Val lookup(const Key& key, const Val& def) const 
    {
      typename std::vector<KeyValue>::const_iterator i = std::lower_bound(vec.begin(), vec.end(), key);
      if (i == vec.end()) return def;
      if (i->key != key) return def;
      return i->val;
    }

    /*! clears all state */
    void clear() {
      vec.clear();
    }

  private:
    std::vector<KeyValue> vec;    //!< vector containing sorted elements
  };
}