boost/interprocess/sync/sharable_lock.hpp
//////////////////////////////////////////////////////////////////////////////
//
// (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.
//
//////////////////////////////////////////////////////////////////////////////
//
// This interface is inspired by Howard Hinnant's lock proposal.
// http://home.twcny.rr.com/hinnant/cpp_extensions/threads_move.html
//
//////////////////////////////////////////////////////////////////////////////
#ifndef BOOST_INTERPROCESS_SHARABLE_LOCK_HPP
#define BOOST_INTERPROCESS_SHARABLE_LOCK_HPP
#if (defined _MSC_VER) && (_MSC_VER >= 1200)
# pragma once
#endif
#include <boost/interprocess/detail/config_begin.hpp>
#include <boost/interprocess/detail/workaround.hpp>
#include <boost/interprocess/interprocess_fwd.hpp>
#include <boost/interprocess/sync/lock_options.hpp>
#include <boost/interprocess/exceptions.hpp>
#include <boost/interprocess/detail/mpl.hpp>
#include <boost/interprocess/detail/type_traits.hpp>
#include <boost/move/move.hpp>
#include <boost/interprocess/detail/posix_time_types_wrk.hpp>
//!\file
//!Describes the upgradable_lock class that serves to acquire the upgradable
//!lock of a mutex.
namespace boost {
namespace interprocess {
//!sharable_lock is meant to carry out the tasks for sharable-locking
//!(such as read-locking), unlocking, try-sharable-locking and timed-sharable-locking
//!(recursive or not) for the Mutex. The Mutex need not supply all of this
//!functionality. If the client of sharable_lock<Mutex> does not use functionality which
//!the Mutex does not supply, no harm is done. Mutex ownership can be shared among
//!sharable_locks, and a single upgradable_lock. sharable_lock does not support
//!copy semantics. But sharable_lock supports ownership transfer from an sharable_lock,
//!upgradable_lock and scoped_lock via transfer_lock syntax.*/
template <class SharableMutex>
class sharable_lock
{
public:
typedef SharableMutex mutex_type;
/// @cond
private:
typedef sharable_lock<SharableMutex> this_type;
explicit sharable_lock(scoped_lock<mutex_type>&);
typedef bool this_type::*unspecified_bool_type;
BOOST_MOVABLE_BUT_NOT_COPYABLE(sharable_lock)
/// @endcond
public:
//!Effects: Default constructs a sharable_lock.
//!Postconditions: owns() == false and mutex() == 0.
sharable_lock()
: mp_mutex(0), m_locked(false)
{}
//!Effects: m.lock_sharable().
//!Postconditions: owns() == true and mutex() == &m.
//!Notes: The constructor will take sharable-ownership of the mutex. If
//! another thread already owns the mutex with exclusive ownership
//! (scoped_lock), this thread will block until the mutex is released.
//! If another thread owns the mutex with sharable or upgradable ownership,
//! then no blocking will occur. Whether or not this constructor handles
//! recursive locking depends upon the mutex.
explicit sharable_lock(mutex_type& m)
: mp_mutex(&m), m_locked(false)
{ mp_mutex->lock_sharable(); m_locked = true; }
//!Postconditions: owns() == false, and mutex() == &m.
//!Notes: The constructor will not take ownership of the mutex. There is no effect
//! required on the referenced mutex.
sharable_lock(mutex_type& m, defer_lock_type)
: mp_mutex(&m), m_locked(false)
{}
//!Postconditions: owns() == true, and mutex() == &m.
//!Notes: The constructor will suppose that the mutex is already sharable
//! locked. There is no effect required on the referenced mutex.
sharable_lock(mutex_type& m, accept_ownership_type)
: mp_mutex(&m), m_locked(true)
{}
//!Effects: m.try_lock_sharable()
//!Postconditions: mutex() == &m. owns() == the return value of the
//! m.try_lock_sharable() executed within the constructor.
//!Notes: The constructor will take sharable-ownership of the mutex if it
//! can do so without waiting. Whether or not this constructor handles
//! recursive locking depends upon the mutex. If the mutex_type does not
//! support try_lock_sharable, this constructor will fail at compile
//! time if instantiated, but otherwise have no effect.
sharable_lock(mutex_type& m, try_to_lock_type)
: mp_mutex(&m), m_locked(false)
{ m_locked = mp_mutex->try_lock_sharable(); }
//!Effects: m.timed_lock_sharable(abs_time)
//!Postconditions: mutex() == &m. owns() == the return value of the
//! m.timed_lock_sharable() executed within the constructor.
//!Notes: The constructor will take sharable-ownership of the mutex if it
//! can do so within the time specified. Whether or not this constructor
//! handles recursive locking depends upon the mutex. If the mutex_type
//! does not support timed_lock_sharable, this constructor will fail at
//! compile time if instantiated, but otherwise have no effect.
sharable_lock(mutex_type& m, const boost::posix_time::ptime& abs_time)
: mp_mutex(&m), m_locked(false)
{ m_locked = mp_mutex->timed_lock_sharable(abs_time); }
//!Postconditions: mutex() == upgr.mutex(). owns() == the value of upgr.owns()
//! before the construction. upgr.owns() == false after the construction.
//!Notes: If the upgr sharable_lock owns the mutex, ownership is moved to this
//! sharable_lock with no blocking. If the upgr sharable_lock does not own the mutex, then
//! neither will this sharable_lock. Only a moved sharable_lock's will match this
//! signature. An non-moved sharable_lock can be moved with the expression:
//! "boost::move(lock);". This constructor does not alter the state of the mutex,
//! only potentially who owns it.
sharable_lock(BOOST_RV_REF(sharable_lock<mutex_type>) upgr)
: mp_mutex(0), m_locked(upgr.owns())
{ mp_mutex = upgr.release(); }
//!Effects: If upgr.owns() then calls unlock_upgradable_and_lock_sharable() on the
//! referenced mutex.
//!Postconditions: mutex() == the value upgr.mutex() had before the construction.
//! upgr.mutex() == 0 owns() == the value of upgr.owns() before construction.
//! upgr.owns() == false after the construction.
//!Notes: If upgr is locked, this constructor will lock this sharable_lock while
//! unlocking upgr. Only a moved sharable_lock's will match this
//! signature. An non-moved upgradable_lock can be moved with the expression:
//! "boost::move(lock);".*/
template<class T>
sharable_lock(BOOST_RV_REF(upgradable_lock<T>) upgr
, typename ipcdetail::enable_if< ipcdetail::is_same<T, SharableMutex> >::type * = 0)
: mp_mutex(0), m_locked(false)
{
upgradable_lock<mutex_type> &u_lock = upgr;
if(u_lock.owns()){
u_lock.mutex()->unlock_upgradable_and_lock_sharable();
m_locked = true;
}
mp_mutex = u_lock.release();
}
//!Effects: If scop.owns() then calls unlock_and_lock_sharable() on the
//! referenced mutex.
//!Postconditions: mutex() == the value scop.mutex() had before the construction.
//! scop.mutex() == 0 owns() == scop.owns() before the constructor. After the
//! construction, scop.owns() == false.
//!Notes: If scop is locked, this constructor will transfer the exclusive ownership
//! to a sharable-ownership of this sharable_lock.
//! Only a moved scoped_lock's will match this
//! signature. An non-moved scoped_lock can be moved with the expression:
//! "boost::move(lock);".
template<class T>
sharable_lock(BOOST_RV_REF(scoped_lock<T>) scop
, typename ipcdetail::enable_if< ipcdetail::is_same<T, SharableMutex> >::type * = 0)
: mp_mutex(0), m_locked(false)
{
scoped_lock<mutex_type> &e_lock = scop;
if(e_lock.owns()){
e_lock.mutex()->unlock_and_lock_sharable();
m_locked = true;
}
mp_mutex = e_lock.release();
}
//!Effects: if (owns()) mp_mutex->unlock_sharable().
//!Notes: The destructor behavior ensures that the mutex lock is not leaked.
~sharable_lock()
{
try{
if(m_locked && mp_mutex) mp_mutex->unlock_sharable();
}
catch(...){}
}
//!Effects: If owns() before the call, then unlock_sharable() is called on mutex().
//! *this gets the state of upgr and upgr gets set to a default constructed state.
//!Notes: With a recursive mutex it is possible that both this and upgr own the mutex
//! before the assignment. In this case, this will own the mutex after the assignment
//! (and upgr will not), but the mutex's lock count will be decremented by one.
sharable_lock &operator=(BOOST_RV_REF(sharable_lock<mutex_type>) upgr)
{
if(this->owns())
this->unlock();
m_locked = upgr.owns();
mp_mutex = upgr.release();
return *this;
}
//!Effects: If mutex() == 0 or already locked, throws a lock_exception()
//! exception. Calls lock_sharable() on the referenced mutex.
//!Postconditions: owns() == true.
//!Notes: The sharable_lock changes from a state of not owning the
//! mutex, to owning the mutex, blocking if necessary.
void lock()
{
if(!mp_mutex || m_locked)
throw lock_exception();
mp_mutex->lock_sharable();
m_locked = true;
}
//!Effects: If mutex() == 0 or already locked, throws a lock_exception()
//! exception. Calls try_lock_sharable() on the referenced mutex.
//!Postconditions: owns() == the value returned from
//! mutex()->try_lock_sharable().
//!Notes: The sharable_lock changes from a state of not owning the mutex,
//! to owning the mutex, but only if blocking was not required. If the
//! mutex_type does not support try_lock_sharable(), this function will
//! fail at compile time if instantiated, but otherwise have no effect.
bool try_lock()
{
if(!mp_mutex || m_locked)
throw lock_exception();
m_locked = mp_mutex->try_lock_sharable();
return m_locked;
}
//!Effects: If mutex() == 0 or already locked, throws a lock_exception()
//! exception. Calls timed_lock_sharable(abs_time) on the referenced mutex.
//!Postconditions: owns() == the value returned from
//! mutex()->timed_lock_sharable(elps_time).
//!Notes: The sharable_lock changes from a state of not owning the mutex,
//! to owning the mutex, but only if it can obtain ownership within the
//! specified time interval. If the mutex_type does not support
//! timed_lock_sharable(), this function will fail at compile time if
//! instantiated, but otherwise have no effect.
bool timed_lock(const boost::posix_time::ptime& abs_time)
{
if(!mp_mutex || m_locked)
throw lock_exception();
m_locked = mp_mutex->timed_lock_sharable(abs_time);
return m_locked;
}
//!Effects: If mutex() == 0 or not locked, throws a lock_exception() exception.
//! Calls unlock_sharable() on the referenced mutex.
//!Postconditions: owns() == false.
//!Notes: The sharable_lock changes from a state of owning the mutex, to
//! not owning the mutex.
void unlock()
{
if(!mp_mutex || !m_locked)
throw lock_exception();
mp_mutex->unlock_sharable();
m_locked = false;
}
//!Effects: Returns true if this scoped_lock has
//!acquired the referenced mutex.
bool owns() const
{ return m_locked && mp_mutex; }
//!Conversion to bool.
//!Returns owns().
operator unspecified_bool_type() const
{ return m_locked? &this_type::m_locked : 0; }
//!Effects: Returns a pointer to the referenced mutex, or 0 if
//!there is no mutex to reference.
mutex_type* mutex() const
{ return mp_mutex; }
//!Effects: Returns a pointer to the referenced mutex, or 0 if there is no
//! mutex to reference.
//!Postconditions: mutex() == 0 and owns() == false.
mutex_type* release()
{
mutex_type *mut = mp_mutex;
mp_mutex = 0;
m_locked = false;
return mut;
}
//!Effects: Swaps state with moved lock.
//!Throws: Nothing.
void swap(sharable_lock<mutex_type> &other)
{
std::swap(mp_mutex, other.mp_mutex);
std::swap(m_locked, other.m_locked);
}
/// @cond
private:
mutex_type *mp_mutex;
bool m_locked;
/// @endcond
};
} // namespace interprocess
} // namespace boost
#include <boost/interprocess/detail/config_end.hpp>
#endif // BOOST_INTERPROCESS_SHARABLE_LOCK_HPP