mosesdecoder/moses/thread_safe_container.h

// -*- c++ -*-
#pragma once
#include "moses/Util.h"
#ifdef WITH_THREADS

#include <time.h>
#include <boost/thread.hpp>
#include <boost/scoped_ptr.hpp>
#include <boost/shared_ptr.hpp>
#include <boost/weak_ptr.hpp>

#include "moses/TargetPhrase.h"
#include <boost/thread/shared_mutex.hpp>
#include <boost/thread/locks.hpp>

#include <map>

namespace Moses
{

// todo: replace this with thread lock-free containers, if a stable library can
//       be found somewhere

template<typename KEY, typename VAL, class CONTAINER = std::map<KEY,VAL> >
class
ThreadSafeContainer
{
protected:
  mutable boost::shared_mutex m_lock;
  CONTAINER m_container;
  typedef typename CONTAINER::iterator iter_t;
  typedef typename CONTAINER::const_iterator const_iter_t;
  typedef typename CONTAINER::value_type entry_t;
public:

  class locking_iterator
  {
    boost::unique_lock<boost::shared_mutex> m_lock;
    CONTAINER const* m_container;
    const_iter_t m_iter;

    locking_iterator(locking_iterator const& other); // no copies!
  public:
    locking_iterator() : m_container(NULL) { }

    locking_iterator(boost::shared_mutex& lock,
                     CONTAINER const* container,
                     const_iter_t const& iter)
      : m_lock(lock), m_container(container), m_iter(iter)
    { }

    entry_t const& operator->() 
    {
      UTIL_THROW_IF2(m_container == NULL, "This locking iterator is invalid "
                     << "or has not been assigned.");
      return m_iter.operator->();
    }
    
    // locking operators transfer the lock upon assignment and become
    // invalid
    locking_iterator const&
    operator=(locking_iterator& other) 
    {
      m_lock.swap(other.m_lock);
      m_iter = other.m_iter;
      other.m_iter = other.m_container.end();
    }
    
    bool
    operator==(const_iter_t const& other) 
    {
      return m_iter == other;
    }
    
    locking_iterator const&
    operator++() 
    { 
      ++m_iter; 
      return *this;
    }

    // DO NOT DEFINE THE POST-INCREMENT OPERATOR!
    // locking_operators are non-copyable,
    // so we can't simply make a copy before incrementing and return
    // the copy after incrementing
    locking_iterator const&
    operator++(int);
  };

  const_iter_t const& 
  end() const 
  {
    return m_container.end();
  }

  locking_iterator 
  begin() const 
  {
    return locking_iterator(m_lock, this, m_container.begin());
  }

  VAL const& 
  set(KEY const& key, VAL const& val) 
  {
    boost::unique_lock< boost::shared_mutex > lock(m_lock);
    entry_t entry(key,val);
    iter_t foo = m_container.insert(entry).first;
    foo->second = val;
    return foo->second;
  }

  VAL const* 
  get(KEY const& key, VAL const& default_val) 
  {
    boost::unique_lock< boost::shared_mutex > lock(m_lock);
    entry_t entry(key, default_val);
    iter_t foo = m_container.insert(entry).first;
    return &(foo->second);
  }

  VAL const* 
  get(KEY const& key) const 
  {
    boost::shared_lock< boost::shared_mutex > lock(m_lock);
    const_iter_t m = m_container.find(key);
    if (m == m_container.end()) return NULL;
    return &m->second;
  }
  
  size_t 
  erase(KEY const& key) 
  {
    boost::unique_lock< boost::shared_mutex > lock(m_lock);
    return m_container.erase(key);
  }
};
}
#endif