LockedHandle.h

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/***********************************************************************************\
* (c) Copyright 1998-2025 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.                                             *
\***********************************************************************************/
#pragma once
 
#include <mutex>
 
template <class T, class MutexType = std::mutex>
class LockedHandle {
public:
  LockedHandle( T* ptr, MutexType& mut ) : m_ptr( ptr ), m_mutex( &mut ) {}
  LockedHandle( T* ptr, MutexType* mut ) : m_ptr( ptr ), m_mutex( mut ) {}
  LockedHandle( T* ptr ) : m_ptr( ptr ), m_mutex( 0 ) {}
  LockedHandle() : m_ptr( nullptr ), m_mutex( nullptr ) {}
 
  void set( T* ptr, MutexType* mut ) {
    m_ptr   = ptr;
    m_mutex = mut;
  }
 
  void setMutex( MutexType* mut ) { m_mutex = mut; }
 
  T* get() const { return m_ptr; }
 
  class Guard {
    Guard( const Guard& a ) = delete;
 
  public:
    Guard( Guard&& a ) : m_ptr( a.m_ptr ), m_mutex( a.m_mutex ) { a.m_mutex = nullptr; }
 
    Guard( T* ptr, MutexType& mutex ) : m_ptr( ptr ), m_mutex( &mutex ) { m_mutex->lock(); }
    ~Guard() { m_mutex->unlock(); }
    T& operator*() { return *m_ptr; }
    T* operator->() { return m_ptr; }
 
    operator T&() { return *m_ptr; }
 
  private:
    T*         m_ptr{ nullptr };
    MutexType* m_mutex{ nullptr };
  };
 
  class ConstGuard {
    ConstGuard( const ConstGuard& a ) = delete;
 
  public:
    ConstGuard( ConstGuard&& a ) : m_ptr( a.m_ptr ), m_mutex( a.m_mutex ) { a.m_mutex = nullptr; }
 
    ConstGuard( const T* ptr, MutexType& mutex ) : m_ptr( ptr ), m_mutex( &mutex ) { m_mutex->lock(); }
    ~ConstGuard() { m_mutex->unlock(); }
    const T& operator*() const { return *m_ptr; }
    const T* operator->() const { return m_ptr; }
 
    operator const T&() const { return *m_ptr; }
 
  private:
    const T*   m_ptr;
    MutexType* m_mutex;
  };
 
  Guard operator*() { return Guard( m_ptr, *m_mutex ); }
 
  Guard operator->() { return Guard( m_ptr, *m_mutex ); }
 
  ConstGuard operator*() const { return ConstGuard( m_ptr, *m_mutex ); }
 
  ConstGuard operator->() const { return ConstGuard( m_ptr, *m_mutex ); }
 
  operator bool() const { return m_ptr; }
 
private:
  T*                 m_ptr;
  mutable MutexType* m_mutex;
};