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 //////////////////////////////////////////////////////////////////////////////
 //  Code based on Howard Hinnant's shared_mutex class
 //
 // (C) Copyright Howard Hinnant 2007-2010. Distributed under the Boost
 // Software License, Version 1.0. (see http://www.boost.org/LICENSE_1_0.txt)
 //
 // (C) Copyright Ion Gaztanaga 2005-2012. Distributed under the Boost
 // Software License, Version 1.0. (See accompanying file
 // LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
 //
 // See http://www.boost.org/libs/interprocess for documentation.
 //
 //////////////////////////////////////////////////////////////////////////////
 
 #ifndef BOOST_INTERPROCESS_SHARABLE_MUTEX_HPP
 #define BOOST_INTERPROCESS_SHARABLE_MUTEX_HPP
 
 #ifndef BOOST_CONFIG_HPP
 #  include <boost/config.hpp>
 #endif
 #
 #if defined(BOOST_HAS_PRAGMA_ONCE)
 #  pragma once
 #endif
 
 #include <boost/interprocess/detail/config_begin.hpp>
 #include <boost/interprocess/detail/workaround.hpp>
 #include <boost/interprocess/sync/scoped_lock.hpp>
 #include <boost/interprocess/timed_utils.hpp>
 #include <boost/interprocess/sync/interprocess_mutex.hpp>
 #include <boost/interprocess/sync/interprocess_condition.hpp>
 #include <climits>
 
 
 //!\file
 //!Describes interprocess_sharable_mutex class
 
 namespace boost {
 namespace interprocess {
 
 //!Wraps a interprocess_sharable_mutex that can be placed in shared memory and can be
 //!shared between processes. Allows timed lock tries
 class interprocess_sharable_mutex
 {
    //Non-copyable
    interprocess_sharable_mutex(const interprocess_sharable_mutex &);
    interprocess_sharable_mutex &operator=(const interprocess_sharable_mutex &);
 
    friend class interprocess_condition;
    public:
 
    //!Constructs the sharable lock.
    //!Throws interprocess_exception on error.
    interprocess_sharable_mutex();
 
    //!Destroys the sharable lock.
    //!Does not throw.
    ~interprocess_sharable_mutex();
 
    //Exclusive locking
 
    //!Requires: The calling thread does not own the mutex.
    //!
    //!Effects: The calling thread tries to obtain exclusive ownership of the mutex,
    //!   and if another thread has exclusive or sharable ownership of
    //!   the mutex, it waits until it can obtain the ownership.
    //!Throws: interprocess_exception on error.
    //! 
    //!Note: A program may deadlock if the thread that has ownership calls 
    //!   this function. If the implementation can detect the deadlock,
    //!   an exception could be thrown.
    void lock();
 
    //!Requires: The calling thread does not own the mutex.
    //!
    //!Effects: The calling thread tries to acquire exclusive ownership of the mutex
    //!   without waiting. If no other thread has exclusive or sharable
    //!   ownership of the mutex this succeeds.
    //!Returns: If it can acquire exclusive ownership immediately returns true.
    //!   If it has to wait, returns false.
    //!Throws: interprocess_exception on error.
    //! 
    //!Note: A program may deadlock if the thread that has ownership calls 
    //!   this function. If the implementation can detect the deadlock,
    //!   an exception could be thrown.
    bool try_lock();
 
    //!Requires: The calling thread does not own the mutex.
    //!
    //!Effects: The calling thread tries to acquire exclusive ownership of the mutex
    //!   waiting if necessary until no other thread has exclusive or sharable
    //!   ownership of the mutex or abs_time is reached.
    //!Returns: If acquires exclusive ownership, returns true. Otherwise returns false.
    //!Throws: interprocess_exception on error.
    //! 
    //!Note: A program may deadlock if the thread that has ownership calls 
    //!   this function. If the implementation can detect the deadlock,
    //!   an exception could be thrown.
    template<class TimePoint>
    bool timed_lock(const TimePoint &abs_time);
 
    //!Same as `timed_lock`, but this function is modeled after the
    //!standard library interface.
    template<class TimePoint> bool try_lock_until(const TimePoint &abs_time)
    {  return this->timed_lock(abs_time);  }
 
    //!Same as `timed_lock`, but this function is modeled after the
    //!standard library interface.
    template<class Duration>  bool try_lock_for(const Duration &dur)
    {  return this->timed_lock(ipcdetail::duration_to_ustime(dur)); }
 
    //!Precondition: The thread must have exclusive ownership of the mutex.
    //!Effects: The calling thread releases the exclusive ownership of the mutex.
    //!Throws: An exception derived from interprocess_exception on error.
    void unlock();
 
    //Sharable locking
 
    //!Requires: The calling thread does not own the mutex.
    //!
    //!Effects: The calling thread tries to obtain sharable ownership of the mutex,
    //!   and if another thread has exclusive ownership of the mutex,
    //!   waits until it can obtain the ownership.
    //!Throws: interprocess_exception on error.
    //! 
    //!Note: A program may deadlock if the thread that has ownership calls 
    //!   this function. If the implementation can detect the deadlock,
    //!   an exception could be thrown.
    void lock_sharable();
 
    //!Same as `lock_sharable` but with a std-compatible interface
    //! 
    void lock_shared()
    {  this->lock_sharable();  }
 
    //!Requires: The calling thread does not own the mutex.
    //!
    //!Effects: The calling thread tries to acquire sharable ownership of the mutex
    //!   without waiting. If no other thread has exclusive ownership
    //!   of the mutex this succeeds.
    //!Returns: If it can acquire sharable ownership immediately returns true. If it
    //!   has to wait, returns false.
    //!Throws: interprocess_exception on error.
    //! 
    //!Note: A program may deadlock if the thread that has ownership calls 
    //!   this function. If the implementation can detect the deadlock,
    //!   an exception could be thrown.
    bool try_lock_sharable();
 
    //!Same as `try_lock_sharable` but with a std-compatible interface
    //! 
    bool try_lock_shared()
    {  return this->try_lock_sharable();  }
 
    //!Requires: The calling thread does not own the mutex.
    //!
    //!Effects: The calling thread tries to acquire sharable ownership of the mutex
    //!   waiting if necessary until no other thread has exclusive
    //!   ownership of the mutex or abs_time is reached.
    //!Returns: If acquires sharable ownership, returns true. Otherwise returns false.
    //!Throws: interprocess_exception on error.
    //! 
    //!Note: A program may deadlock if the thread that has ownership calls 
    //!   this function. If the implementation can detect the deadlock,
    //!   an exception could be thrown.
    template<class TimePoint>
    bool timed_lock_sharable(const TimePoint &abs_time);
 
    //!Same as `timed_lock_sharable`, but this function is modeled after the
    //!standard library interface.
    template<class TimePoint> bool try_lock_shared_until(const TimePoint &abs_time)
    {  return this->timed_lock_sharable(abs_time);  }
 
    //!Same as `timed_lock_sharable`, but this function is modeled after the
    //!standard library interface.
    template<class Duration>  bool try_lock_shared_for(const Duration &dur)
    {  return this->timed_lock_sharable(ipcdetail::duration_to_ustime(dur)); }
 
    //!Precondition: The thread must have sharable ownership of the mutex.
    //!Effects: The calling thread releases the sharable ownership of the mutex.
    //!Throws: An exception derived from interprocess_exception on error.
    void unlock_sharable();
 
    //!Same as `unlock_sharable` but with a std-compatible interface
    //! 
    void unlock_shared()
    {  this->unlock_sharable();  }
 
    #if !defined(BOOST_INTERPROCESS_DOXYGEN_INVOKED)
    private:
    typedef scoped_lock<interprocess_mutex> scoped_lock_t;
 
    //Pack all the control data in a word to be able
    //to use atomic instructions in the future
    struct control_word_t
    {
       unsigned exclusive_in   : 1;
       unsigned num_shared     : sizeof(unsigned)*CHAR_BIT-1;
    }                       m_ctrl;
 
    interprocess_mutex      m_mut;
    interprocess_condition  m_first_gate;
    interprocess_condition  m_second_gate;
 
    private:
    //Rollback structures for exceptions or failure return values
    struct exclusive_rollback
    {
       exclusive_rollback(control_word_t         &ctrl
                         ,interprocess_condition &first_gate)
          :  mp_ctrl(&ctrl), m_first_gate(first_gate)
       {}
 
       void release()
       {  mp_ctrl = 0;   }
 
       ~exclusive_rollback()
       {
          if(mp_ctrl){
             mp_ctrl->exclusive_in = 0;
             m_first_gate.notify_all();
          }
       }
       control_word_t          *mp_ctrl;
       interprocess_condition  &m_first_gate;
    };
 
    template<int Dummy>
    struct base_constants_t
    {
       static const unsigned max_readers
          = ~(unsigned(1) << (sizeof(unsigned)*CHAR_BIT-1));
    };
    typedef base_constants_t<0> constants;
    #endif   //#ifndef BOOST_INTERPROCESS_DOXYGEN_INVOKED
 };
 
 #if !defined(BOOST_INTERPROCESS_DOXYGEN_INVOKED)
 
 template <int Dummy>
 const unsigned interprocess_sharable_mutex::base_constants_t<Dummy>::max_readers;
 
 inline interprocess_sharable_mutex::interprocess_sharable_mutex()
 {
    this->m_ctrl.exclusive_in  = 0;
    this->m_ctrl.num_shared   = 0;
 }
 
 inline interprocess_sharable_mutex::~interprocess_sharable_mutex()
 {}
 
 inline void interprocess_sharable_mutex::lock()
 {
    scoped_lock_t lck(m_mut);
 
    //The exclusive lock must block in the first gate
    //if an exclusive lock has been acquired
    while (this->m_ctrl.exclusive_in){
       this->m_first_gate.wait(lck);
    }
 
    //Mark that exclusive lock has been acquired
    this->m_ctrl.exclusive_in = 1;
 
    //Prepare rollback
    exclusive_rollback rollback(this->m_ctrl, this->m_first_gate);
 
    //Now wait until all readers are gone
    while (this->m_ctrl.num_shared){
       this->m_second_gate.wait(lck);
    }
    rollback.release();
 }
 
 inline bool interprocess_sharable_mutex::try_lock()
 {
    scoped_lock_t lck(m_mut, try_to_lock);
 
    //If we can't lock or any has there is any exclusive
    //or sharable mark return false;
    if(!lck.owns()
       || this->m_ctrl.exclusive_in
       || this->m_ctrl.num_shared){
       return false;
    }
    this->m_ctrl.exclusive_in = 1;
    return true;
 }
 
 template<class TimePoint>
 inline bool interprocess_sharable_mutex::timed_lock
    (const TimePoint &abs_time)
 {
    scoped_lock_t lck(m_mut, abs_time);
    if(!lck.owns())   return false;
 
    //The exclusive lock must block in the first gate
    //if an exclusive lock has been acquired
    while (this->m_ctrl.exclusive_in){
       //Mutexes and condvars handle just fine infinite abs_times
       //so avoid checking it here
       if(!this->m_first_gate.timed_wait(lck, abs_time)){
          if(this->m_ctrl.exclusive_in){
             return false;
          }
          break;
       }
    }
 
    //Mark that exclusive lock has been acquired
    this->m_ctrl.exclusive_in = 1;
 
    //Prepare rollback
    exclusive_rollback rollback(this->m_ctrl, this->m_first_gate);
 
    //Now wait until all readers are gone
    while (this->m_ctrl.num_shared){
       //Mutexes and condvars handle just fine infinite abs_times
       //so avoid checking it here
       if(!this->m_second_gate.timed_wait(lck, abs_time)){
          if(this->m_ctrl.num_shared){
             return false;
          }
          break;
       }
    }
    rollback.release();
    return true;
 }
 
 inline void interprocess_sharable_mutex::unlock()
 {
    scoped_lock_t lck(m_mut);
    this->m_ctrl.exclusive_in = 0;
    this->m_first_gate.notify_all();
 }
 
 //Sharable locking
 
 inline void interprocess_sharable_mutex::lock_sharable()
 {
    scoped_lock_t lck(m_mut);
 
    //The sharable lock must block in the first gate
    //if an exclusive lock has been acquired
    //or there are too many sharable locks
    while(this->m_ctrl.exclusive_in
         || this->m_ctrl.num_shared == constants::max_readers){
       this->m_first_gate.wait(lck);
    }
 
    //Increment sharable count
    ++this->m_ctrl.num_shared;
 }
 
 inline bool interprocess_sharable_mutex::try_lock_sharable()
 {
    scoped_lock_t lck(m_mut, try_to_lock);
 
    //The sharable lock must fail
    //if an exclusive lock has been acquired
    //or there are too many sharable locks
    if(!lck.owns()
       || this->m_ctrl.exclusive_in
       || this->m_ctrl.num_shared == constants::max_readers){
       return false;
    }
 
    //Increment sharable count
    ++this->m_ctrl.num_shared;
    return true;
 }
 
 template<class TimePoint>
 inline bool interprocess_sharable_mutex::timed_lock_sharable
    (const TimePoint &abs_time)
 {
    scoped_lock_t lck(m_mut, abs_time);
    if(!lck.owns())   return false;
 
    //The sharable lock must block in the first gate
    //if an exclusive lock has been acquired
    //or there are too many sharable locks
    while (this->m_ctrl.exclusive_in
          || this->m_ctrl.num_shared == constants::max_readers){
       //Mutexes and condvars handle just fine infinite abs_times
       //so avoid checking it here
       if(!this->m_first_gate.timed_wait(lck, abs_time)){
          if(this->m_ctrl.exclusive_in
                || this->m_ctrl.num_shared == constants::max_readers){
             return false;
          }
          break;
       }
    }
 
    //Increment sharable count
    ++this->m_ctrl.num_shared;
    return true;
 }
 
 inline void interprocess_sharable_mutex::unlock_sharable()
 {
    scoped_lock_t lck(m_mut);
    //Decrement sharable count
    --this->m_ctrl.num_shared;
    if (this->m_ctrl.num_shared == 0){
       this->m_second_gate.notify_one();
    }
    //Check if there are blocked sharables because of
    //there were too many sharables
    else if(this->m_ctrl.num_shared == (constants::max_readers-1)){
       this->m_first_gate.notify_all();
    }
 }
 
 #endif   //#ifndef BOOST_INTERPROCESS_DOXYGEN_INVOKED
 
 }  //namespace interprocess {
 }  //namespace boost {
 
 #include <boost/interprocess/detail/config_end.hpp>
 
 #endif   //BOOST_INTERPROCESS_SHARABLE_MUTEX_HPP

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