SXMutex.h

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/*
// $Id: //open/dev/fennel/synch/SXMutex.h#15 $
// Fennel is a library of data storage and processing components.
// Copyright (C) 2005-2009 The Eigenbase Project
// Copyright (C) 2005-2009 SQLstream, Inc.
// Copyright (C) 2005-2009 LucidEra, Inc.
// Portions Copyright (C) 1999-2009 John V. Sichi
//
// This program is free software; you can redistribute it and/or modify it
// under the terms of the GNU General Public License as published by the Free
// Software Foundation; either version 2 of the License, or (at your option)
// any later version approved by The Eigenbase Project.
//
// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.
//
// You should have received a copy of the GNU General Public License
// along with this program; if not, write to the Free Software
// Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
*/

#ifndef Fennel_SXMutex_Included
#define Fennel_SXMutex_Included

#include "fennel/synch/SynchMonitoredObject.h"
#include "fennel/synch/LockHolderId.h"
#include <boost/utility.hpp>

FENNEL_BEGIN_NAMESPACE

// NOTE jvs 25-Oct-2008:  We can't replace this class with
// boost::shared_mutex, because lock ownership need to be transaction-scoped
// rather than thread-scoped.

class FENNEL_SYNCH_EXPORT SXMutex : public SynchMonitoredObject
{
public:
    enum SchedulingPolicy
    {
        SCHEDULE_DEFAULT,

        SCHEDULE_FAVOR_EXCLUSIVE
    };

    explicit SXMutex();
    ~SXMutex();

    bool waitFor(
        LockMode lockMode,uint iTimeout = ETERNITY,
        TxnId txnId = IMPLICIT_TXN_ID);
    void release(LockMode lockMode, TxnId txnId = IMPLICIT_TXN_ID);
    bool tryUpgrade(TxnId txnId = IMPLICIT_TXN_ID);

    bool isLocked(LockMode lockdMode) const;
    void setSchedulingPolicy(SchedulingPolicy schedulingPolicy);

private:
    SchedulingPolicy schedulingPolicy;
    uint nShared,nExclusive,nExclusivePending;
    LockHolderId exclusiveHolderId;
};

template<LockMode lockMode>
class SXMutexGuard : public boost::noncopyable
{
    SXMutex &rwLock;
    bool m_locked;

public:
    explicit SXMutexGuard(SXMutex& mx, bool initially_locked = true)
        : rwLock(mx), m_locked(false)
    {
        if (initially_locked) {
            lock();
        }
    }

    ~SXMutexGuard()
    {
        if (m_locked) {
            unlock();
        }
    }

    void lock()
    {
        assert(!m_locked);
        rwLock.waitFor(lockMode);
        m_locked = true;
    }

    void unlock()
    {
        assert(m_locked);
        rwLock.release(lockMode);
        m_locked = false;
    }

    bool locked() const
    {
        return m_locked;
    }

    operator const void*() const
    {
        return m_locked ? this : 0;
    }
};

typedef SXMutexGuard<LOCKMODE_S> SXMutexSharedGuard;
typedef SXMutexGuard<LOCKMODE_X> SXMutexExclusiveGuard;

FENNEL_END_NAMESPACE

#endif

// End SXMutex.h

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