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 /***********************************************************************************\
 * (c) Copyright 1998-2019 CERN for the benefit of the LHCb and ATLAS collaborations *
 *                                                                                   *
 * This software is distributed under the terms of the Apache version 2 licence,     *
 * copied verbatim in the file "LICENSE".                                            *
 *                                                                                   *
 * In applying this licence, CERN does not waive the privileges and immunities       *
 * granted to it by virtue of its status as an Intergovernmental Organization        *
 * or submit itself to any jurisdiction.                                             *
 \***********************************************************************************/
 #ifndef _GAUDI_CONTEXTSPECIFICPTR_H_
 #define _GAUDI_CONTEXTSPECIFICPTR_H_
 
 #include <functional>
 #include <mutex>
 #include <numeric>
 #include <type_traits>
 #include <unordered_map>
 
 // For the definition of GAUDI_API
 #include "GaudiKernel/Kernel.h"
 #include "GaudiKernel/ThreadLocalContext.h"
 
 class EventContext;
 
 namespace Gaudi {
   namespace Hive {
     /**
      *  Simple implementation of a smart pointer with different values for
      *  different event contexts (slots).
      *
      *  When the copy for a new context is requested, the returned pointer is
      *  null.
      *
      *  The interface is meant to allow for a drop-in replacement for regular
      *  pointers. It's still responsibility of the user to delete the memory
      *  associated to the pointers.
      */
     template <typename T>
     class ContextSpecificPtr {
     private:
       /// Type used for the internal storage.
       typedef std::unordered_map<ContextIdType, T*> StorageType;
 
     public:
       /// Return the pointer for the current context (null for a new context).
       T* get() const {
         auto lock = std::scoped_lock{ m_ptrs_lock };
         return m_ptrs[currentContextId()];
       }
       /// Set the pointer for the current context.
       T*& set( T* ptr ) {
         auto lock                         = std::scoped_lock{ m_ptrs_lock };
         return m_ptrs[currentContextId()] = ptr;
       }
 
       /// Assignment operator (@see set).
       T*& operator=( T* ptr ) { return set( ptr ); }
 
       /// Return true if the pointer is not null.
       bool isValid() const { return get(); }
 
       /// Conversion to boolean (@see isValid).
       operator bool() const { return isValid(); }
 
       /// Comparison with another pointer.
       bool operator==( T* rhs ) const { return get() == rhs; }
 
       /// @{ Dereference operators.
       T&       operator*() { return *get(); }
       const T& operator*() const { return *get(); }
       T*       operator->() { return get(); }
       const T* operator->() const { return get(); }
       /// @}
 
       /// @{Non thread-safe methods.
 
       /// Set to null all the used pointers.
       void clear() { m_ptrs.clear(); }
 
       /// Taking a function f that from a T* produces a value, return the sum of
       /// all the values corresponding to the contained pointers using init as
       /// first value.
       template <class Mapper>
 #if __cplusplus >= 201703L
       auto accumulate( Mapper f, std::invoke_result_t<Mapper, const T*> init ) const -> decltype( init ) {
 #else
       auto accumulate( Mapper f, std::result_of_t<Mapper( const T* )> init ) const -> decltype( init ) {
 #endif
         return accumulate( f, init, std::plus<>() );
       }
 
       /// Taking a function f that from a T* produces a value, return the
       /// accumulated  result, through the operation 'op', of all the values
       /// corresponding to the contained pointers using init as first value.
       template <class Mapper, class BinaryOperation>
 #if __cplusplus >= 201703L
       auto accumulate( Mapper f, std::invoke_result_t<Mapper, const T*> init, BinaryOperation op ) const
 #else
       auto accumulate( Mapper f, std::result_of_t<Mapper( const T* )> init, BinaryOperation op ) const
 #endif
           -> decltype( init ) {
         auto lock = std::scoped_lock{ m_ptrs_lock };
         return std::accumulate( m_ptrs.begin(), m_ptrs.end(), init, [&f, &op]( const auto& partial, const auto& p ) {
           return op( partial, f( p.second ) );
         } );
       }
 
       /// Call a function on each contained pointer.
       template <class F>
       void for_each( F f ) const {
         auto lock = std::scoped_lock{ m_ptrs_lock };
         for ( auto& i : m_ptrs ) f( i.second );
       }
 
       /// Call a function on each contained pointer. (non-const version)
       template <class F>
       void for_each( F f ) {
         auto lock = std::scoped_lock{ m_ptrs_lock };
         for ( auto& i : m_ptrs ) f( i.second );
       }
 
       /// Call a function on each element, passing slot# as well
       template <class F>
       void for_all( F f ) const {
         auto lock = std::scoped_lock{ m_ptrs_lock };
         for ( auto& i : m_ptrs ) f( i.first, i.second );
       }
       template <class F>
       void for_all( F f ) {
         auto lock = std::scoped_lock{ m_ptrs_lock };
         for ( auto& i : m_ptrs ) f( i.first, i.second );
       }
 
       void deleteAll() {
         for_each( []( T*& p ) {
           delete p;
           p = nullptr;
         } );
       }
 
     private:
       /// Internal storage for the different internal pointers.
       mutable StorageType m_ptrs;
       /// Mutex for the m_ptrs container.
       mutable std::mutex m_ptrs_lock;
     };
 
     /**
      *  Implementation of a context specific storage accessible as a sort of
      *  smart reference class.
      *
      *  New values are created from the prototype passed to the constructor.
      */
     template <typename T>
     class ContextSpecificData {
     public:
       /// Constructor with prototype value.
       ContextSpecificData( T proto = {} ) : m_proto( std::move( proto ) ) {}
 
       /// Destructor.
       ~ContextSpecificData() { m_ptr.deleteAll(); }
 
       operator T&() {
         if ( !m_ptr ) m_ptr = new T( m_proto );
         return *m_ptr;
       }
 
       operator T&() const {
         if ( !m_ptr ) m_ptr = new T( m_proto );
         return *m_ptr;
       }
 
       /// Assignment operator.
       T& operator=( const T& other ) { return (T&)( *this ) = other; }
 
       /// Return the sum of all the contained values using init as first value.
       T accumulate( T init ) const { return accumulate( init, std::plus<>() ); }
 
       /// Return the accumulated result, through the operation 'op', of all the
       /// contained values using init as first value.
       template <class T1, class BinaryOperation>
       T1 accumulate( T1 init, BinaryOperation op ) const {
         return m_ptr.accumulate( []( const T* p ) { return *p; }, init, op );
       }
 
       /// Call a function on each contained value.
       template <class F>
       void for_each( F f ) const {
         m_ptr.for_each( [&f]( const T* p ) { f( *p ); } );
       }
 
       /// Call a function on each contained value. (non-const version)
       template <class F>
       void for_each( F f ) {
         m_ptr.for_each( [&f]( T* p ) { f( *p ); } );
       }
 
       /// Call a function on each element, passing slot# as well
       template <class F>
       void for_all( F f ) const {
         m_ptr.for_all( [&f]( size_t s, const T* p ) { f( s, *p ); } );
       }
       template <class F>
       void for_all( F f ) {
         m_ptr.for_all( [&f]( size_t s, T* p ) { f( s, *p ); } );
       }
 
     private:
       // FIXME: implement a proper copy constructor
       ContextSpecificData( const ContextSpecificData& ) = delete;
 
       /// Prototype value.
       T m_proto = {};
       /// Internal implementation.
       mutable ContextSpecificPtr<T> m_ptr;
     };
   } // namespace Hive
 } // namespace Gaudi
 
 #endif // _GAUDI_CONTEXTSPECIFICPTR_H_

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