314 lines
13 KiB
C++
314 lines
13 KiB
C++
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//////////////////////////////////////////////////////////////////////////////
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//
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// (C) Copyright Ion Gaztanaga 2005-2012. Distributed under the Boost
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// Software License, Version 1.0. (See accompanying file
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// LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
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//
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// See http://www.boost.org/libs/interprocess for documentation.
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//
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//////////////////////////////////////////////////////////////////////////////
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//
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// This interface is inspired by Howard Hinnant's lock proposal.
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// http://home.twcny.rr.com/hinnant/cpp_extensions/threads_move.html
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//
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//////////////////////////////////////////////////////////////////////////////
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#ifndef BOOST_INTERPROCESS_UPGRADABLE_LOCK_HPP
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#define BOOST_INTERPROCESS_UPGRADABLE_LOCK_HPP
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#ifndef BOOST_CONFIG_HPP
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# include <boost/config.hpp>
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#endif
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#
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#if defined(BOOST_HAS_PRAGMA_ONCE)
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# pragma once
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#endif
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#include <boost/interprocess/detail/config_begin.hpp>
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#include <boost/interprocess/detail/workaround.hpp>
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#include <boost/interprocess/interprocess_fwd.hpp>
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#include <boost/interprocess/sync/lock_options.hpp>
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#include <boost/interprocess/detail/mpl.hpp>
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#include <boost/interprocess/detail/type_traits.hpp>
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#include <boost/interprocess/exceptions.hpp>
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#include <boost/move/utility_core.hpp>
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#include <boost/interprocess/detail/posix_time_types_wrk.hpp>
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//!\file
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//!Describes the upgradable_lock class that serves to acquire the upgradable
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//!lock of a mutex.
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namespace boost {
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namespace interprocess {
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//!upgradable_lock is meant to carry out the tasks for read-locking, unlocking,
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//!try-read-locking and timed-read-locking (recursive or not) for the Mutex.
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//!Additionally the upgradable_lock can transfer ownership to a scoped_lock
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//!using transfer_lock syntax. The Mutex need not supply all of the functionality.
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//!If the client of upgradable_lock<Mutex> does not use functionality which the
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//!Mutex does not supply, no harm is done. Mutex ownership can be shared among
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//!read_locks, and a single upgradable_lock. upgradable_lock does not support
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//!copy semantics. However upgradable_lock supports ownership transfer from
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//!a upgradable_locks or scoped_locks via transfer_lock syntax.
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template <class UpgradableMutex>
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class upgradable_lock
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{
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public:
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typedef UpgradableMutex mutex_type;
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#if !defined(BOOST_INTERPROCESS_DOXYGEN_INVOKED)
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private:
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typedef upgradable_lock<UpgradableMutex> this_type;
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explicit upgradable_lock(scoped_lock<mutex_type>&);
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typedef bool this_type::*unspecified_bool_type;
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BOOST_MOVABLE_BUT_NOT_COPYABLE(upgradable_lock)
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#endif //#ifndef BOOST_INTERPROCESS_DOXYGEN_INVOKED
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public:
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//!Effects: Default constructs a upgradable_lock.
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//!Postconditions: owns() == false and mutex() == 0.
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upgradable_lock()
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: mp_mutex(0), m_locked(false)
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{}
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explicit upgradable_lock(mutex_type& m)
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: mp_mutex(&m), m_locked(false)
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{ mp_mutex->lock_upgradable(); m_locked = true; }
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//!Postconditions: owns() == false, and mutex() == &m.
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//!Notes: The constructor will not take ownership of the mutex. There is no effect
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//! required on the referenced mutex.
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upgradable_lock(mutex_type& m, defer_lock_type)
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: mp_mutex(&m), m_locked(false)
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{}
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//!Postconditions: owns() == true, and mutex() == &m.
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//!Notes: The constructor will suppose that the mutex is already upgradable
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//! locked. There is no effect required on the referenced mutex.
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upgradable_lock(mutex_type& m, accept_ownership_type)
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: mp_mutex(&m), m_locked(true)
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{}
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//!Effects: m.try_lock_upgradable().
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//!Postconditions: mutex() == &m. owns() == the return value of the
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//! m.try_lock_upgradable() executed within the constructor.
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//!Notes: The constructor will take upgradable-ownership of the mutex
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//! if it can do so without waiting. Whether or not this constructor
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//! handles recursive locking depends upon the mutex. If the mutex_type
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//! does not support try_lock_upgradable, this constructor will fail at
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//! compile time if instantiated, but otherwise have no effect.
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upgradable_lock(mutex_type& m, try_to_lock_type)
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: mp_mutex(&m), m_locked(false)
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{ m_locked = mp_mutex->try_lock_upgradable(); }
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//!Effects: m.timed_lock_upgradable(abs_time)
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//!Postconditions: mutex() == &m. owns() == the return value of the
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//! m.timed_lock_upgradable() executed within the constructor.
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//!Notes: The constructor will take upgradable-ownership of the mutex if it
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//! can do so within the time specified. Whether or not this constructor
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//! handles recursive locking depends upon the mutex. If the mutex_type
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//! does not support timed_lock_upgradable, this constructor will fail
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//! at compile time if instantiated, but otherwise have no effect.
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upgradable_lock(mutex_type& m, const boost::posix_time::ptime& abs_time)
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: mp_mutex(&m), m_locked(false)
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{ m_locked = mp_mutex->timed_lock_upgradable(abs_time); }
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//!Effects: No effects on the underlying mutex.
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//!Postconditions: mutex() == the value upgr.mutex() had before the
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//! construction. upgr.mutex() == 0. owns() == upgr.owns() before the
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//! construction. upgr.owns() == false.
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//!Notes: If upgr is locked, this constructor will lock this upgradable_lock
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//! while unlocking upgr. If upgr is unlocked, then this upgradable_lock will
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//! be unlocked as well. Only a moved upgradable_lock's will match this
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//! signature. An non-moved upgradable_lock can be moved with the
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//! expression: "boost::move(lock);". This constructor does not alter the
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//! state of the mutex, only potentially who owns it.
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upgradable_lock(BOOST_RV_REF(upgradable_lock<mutex_type>) upgr)
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: mp_mutex(0), m_locked(upgr.owns())
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{ mp_mutex = upgr.release(); }
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//!Effects: If scop.owns(), m_.unlock_and_lock_upgradable().
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//!Postconditions: mutex() == the value scop.mutex() had before the construction.
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//! scop.mutex() == 0. owns() == scop.owns() before the constructor. After the
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//! construction, scop.owns() == false.
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//!Notes: If scop is locked, this constructor will transfer the exclusive-ownership
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//! to an upgradable-ownership of this upgradable_lock.
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//! Only a moved sharable_lock's will match this
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//! signature. An non-moved sharable_lock can be moved with the
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//! expression: "boost::move(lock);".
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template<class T>
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upgradable_lock(BOOST_RV_REF(scoped_lock<T>) scop
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, typename ipcdetail::enable_if< ipcdetail::is_same<T, UpgradableMutex> >::type * = 0)
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: mp_mutex(0), m_locked(false)
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{
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scoped_lock<mutex_type> &u_lock = scop;
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if(u_lock.owns()){
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u_lock.mutex()->unlock_and_lock_upgradable();
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m_locked = true;
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}
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mp_mutex = u_lock.release();
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}
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//!Effects: If shar.owns() then calls try_unlock_sharable_and_lock_upgradable()
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//! on the referenced mutex.
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//! a)if try_unlock_sharable_and_lock_upgradable() returns true then mutex()
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//! obtains the value from shar.release() and owns() is set to true.
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//! b)if try_unlock_sharable_and_lock_upgradable() returns false then shar is
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//! unaffected and this upgradable_lock construction has the same
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//! effects as a default construction.
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//! c)Else shar.owns() is false. mutex() obtains the value from shar.release()
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//! and owns() is set to false.
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//!Notes: This construction will not block. It will try to obtain mutex
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//! ownership from shar immediately, while changing the lock type from a
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//! "read lock" to an "upgradable lock". If the "read lock" isn't held
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//! in the first place, the mutex merely changes type to an unlocked
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//! "upgradable lock". If the "read lock" is held, then mutex transfer
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//! occurs only if it can do so in a non-blocking manner.
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template<class T>
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upgradable_lock( BOOST_RV_REF(sharable_lock<T>) shar, try_to_lock_type
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, typename ipcdetail::enable_if< ipcdetail::is_same<T, UpgradableMutex> >::type * = 0)
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: mp_mutex(0), m_locked(false)
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{
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sharable_lock<mutex_type> &s_lock = shar;
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if(s_lock.owns()){
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if((m_locked = s_lock.mutex()->try_unlock_sharable_and_lock_upgradable()) == true){
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mp_mutex = s_lock.release();
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}
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}
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else{
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s_lock.release();
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}
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}
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//!Effects: if (owns()) m_->unlock_upgradable().
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//!Notes: The destructor behavior ensures that the mutex lock is not leaked.
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~upgradable_lock()
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{
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try{
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if(m_locked && mp_mutex) mp_mutex->unlock_upgradable();
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}
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catch(...){}
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}
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//!Effects: If owns(), then unlock_upgradable() is called on mutex().
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//! *this gets the state of upgr and upgr gets set to a default constructed state.
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//!Notes: With a recursive mutex it is possible that both this and upgr own the
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//! mutex before the assignment. In this case, this will own the mutex
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//! after the assignment (and upgr will not), but the mutex's upgradable lock
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//! count will be decremented by one.
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upgradable_lock &operator=(BOOST_RV_REF(upgradable_lock) upgr)
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{
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if(this->owns())
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this->unlock();
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m_locked = upgr.owns();
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mp_mutex = upgr.release();
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return *this;
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}
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//!Effects: If mutex() == 0 or if already locked, throws a lock_exception()
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//! exception. Calls lock_upgradable() on the referenced mutex.
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//!Postconditions: owns() == true.
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//!Notes: The sharable_lock changes from a state of not owning the mutex,
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//! to owning the mutex, blocking if necessary.
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void lock()
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{
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if(!mp_mutex || m_locked)
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throw lock_exception();
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mp_mutex->lock_upgradable();
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m_locked = true;
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}
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//!Effects: If mutex() == 0 or if already locked, throws a lock_exception()
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//! exception. Calls try_lock_upgradable() on the referenced mutex.
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//!Postconditions: owns() == the value returned from
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//! mutex()->try_lock_upgradable().
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//!Notes: The upgradable_lock changes from a state of not owning the mutex,
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//! to owning the mutex, but only if blocking was not required. If the
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//! mutex_type does not support try_lock_upgradable(), this function will
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//! fail at compile time if instantiated, but otherwise have no effect.
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bool try_lock()
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{
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if(!mp_mutex || m_locked)
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throw lock_exception();
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m_locked = mp_mutex->try_lock_upgradable();
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return m_locked;
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}
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//!Effects: If mutex() == 0 or if already locked, throws a lock_exception()
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//! exception. Calls timed_lock_upgradable(abs_time) on the referenced mutex.
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//!Postconditions: owns() == the value returned from
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//! mutex()->timed_lock_upgradable(abs_time).
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//!Notes: The upgradable_lock changes from a state of not owning the mutex,
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//! to owning the mutex, but only if it can obtain ownership within the
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//! specified time. If the mutex_type does not support
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//! timed_lock_upgradable(abs_time), this function will fail at compile
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//! time if instantiated, but otherwise have no effect.
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bool timed_lock(const boost::posix_time::ptime& abs_time)
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{
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if(!mp_mutex || m_locked)
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throw lock_exception();
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m_locked = mp_mutex->timed_lock_upgradable(abs_time);
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return m_locked;
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}
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//!Effects: If mutex() == 0 or if not locked, throws a lock_exception()
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//! exception. Calls unlock_upgradable() on the referenced mutex.
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//!Postconditions: owns() == false.
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//!Notes: The upgradable_lock changes from a state of owning the mutex,
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//! to not owning the mutex.
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void unlock()
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{
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if(!mp_mutex || !m_locked)
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throw lock_exception();
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mp_mutex->unlock_upgradable();
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m_locked = false;
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}
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//!Effects: Returns true if this scoped_lock has acquired the
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//!referenced mutex.
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bool owns() const
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{ return m_locked && mp_mutex; }
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//!Conversion to bool.
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//!Returns owns().
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operator unspecified_bool_type() const
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{ return m_locked? &this_type::m_locked : 0; }
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//!Effects: Returns a pointer to the referenced mutex, or 0 if
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//!there is no mutex to reference.
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mutex_type* mutex() const
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{ return mp_mutex; }
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//!Effects: Returns a pointer to the referenced mutex, or 0 if there is no
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//! mutex to reference.
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//!Postconditions: mutex() == 0 and owns() == false.
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mutex_type* release()
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{
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mutex_type *mut = mp_mutex;
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mp_mutex = 0;
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m_locked = false;
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return mut;
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}
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//!Effects: Swaps state with moved lock.
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//!Throws: Nothing.
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void swap(upgradable_lock<mutex_type> &other)
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{
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(simple_swap)(mp_mutex, other.mp_mutex);
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(simple_swap)(m_locked, other.m_locked);
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}
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#if !defined(BOOST_INTERPROCESS_DOXYGEN_INVOKED)
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private:
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mutex_type *mp_mutex;
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bool m_locked;
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#endif //#ifndef BOOST_INTERPROCESS_DOXYGEN_INVOKED
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};
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} // namespace interprocess
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} // namespace boost
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#include <boost/interprocess/detail/config_end.hpp>
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#endif // BOOST_INTERPROCESS_UPGRADABLE_LOCK_HPP
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