virtualbox/include/iprt/cpp/lock.h

/** @file
 * IPRT - Classes for Scope-based Locking.
 */

/*
 * Copyright (C) 2007-2024 Oracle and/or its affiliates.
 *
 * This file is part of VirtualBox base platform packages, as
 * available from https://www.virtualbox.org.
 *
 * 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, in version 3 of the
 * License.
 *
 * 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, see <https://www.gnu.org/licenses>.
 *
 * The contents of this file may alternatively be used under the terms
 * of the Common Development and Distribution License Version 1.0
 * (CDDL), a copy of it is provided in the "COPYING.CDDL" file included
 * in the VirtualBox distribution, in which case the provisions of the
 * CDDL are applicable instead of those of the GPL.
 *
 * You may elect to license modified versions of this file under the
 * terms and conditions of either the GPL or the CDDL or both.
 *
 * SPDX-License-Identifier: GPL-3.0-only OR CDDL-1.0
 */

#ifndef IPRT_INCLUDED_cpp_lock_h
#define IPRT_INCLUDED_cpp_lock_h
#ifndef RT_WITHOUT_PRAGMA_ONCE
# pragma once
#endif

#include <iprt/critsect.h>
#ifdef RT_LOCK_STRICT
# include <iprt/lockvalidator.h>
#endif

RT_C_DECLS_BEGIN

/** @defgroup grp_rt_cpp_lock       C++ Scope-based Locking
 * @ingroup grp_rt_cpp
 * @{
 */

class RTCLock;

/**
 * The mutex lock.
 *
 * This is used as an object data member if the intention is to lock
 * a single object. This can also be used statically, initialized in
 * a global variable, for class wide purposes.
 *
 * This is best used together with RTCLock.
 */
class RTCLockMtx
{
friend class RTCLock;

private:
    RTCRITSECT      mMtx;

public:
    RTCLockMtx()
    {
#ifdef RT_LOCK_STRICT_ORDER
        RTCritSectInitEx(&mMtx, 0 /*fFlags*/,
                         RTLockValidatorClassCreateUnique(RT_SRC_POS, NULL),
                         RTLOCKVAL_SUB_CLASS_NONE, NULL);
#else
        RTCritSectInit(&mMtx);
#endif
    }

    /** Use to when creating locks that belongs in the same "class".  */
    RTCLockMtx(RT_SRC_POS_DECL, uint32_t uSubClass = RTLOCKVAL_SUB_CLASS_NONE)
    {
#ifdef RT_LOCK_STRICT_ORDER
        RTCritSectInitEx(&mMtx, 0 /*fFlags*/,
                         RTLockValidatorClassForSrcPos(RT_SRC_POS_ARGS, NULL),
                         uSubClass, NULL);
#else
        NOREF(uSubClass);
        RTCritSectInit(&mMtx);
        RT_SRC_POS_NOREF();
#endif
    }

    ~RTCLockMtx()
    {
        RTCritSectDelete(&mMtx);
    }

    /* lock() and unlock() are private so that only friend RTCLock can access
       them. */
private:
    inline void lock()
    {
        RTCritSectEnter(&mMtx);
    }

    inline void unlock()
    {
        RTCritSectLeave(&mMtx);
    }
};


/**
 * The stack object for automatic locking and unlocking.
 *
 * This is a helper class for automatic locks, to simplify requesting a
 * RTCLockMtx and to not forget releasing it.  To request a RTCLockMtx, simply
 * create an instance of RTCLock on the stack and pass the mutex to it:
 *
 * @code
    extern RTCLockMtx gMtx;     // wherever this is
    ...
    if (...)
    {
        RTCLock lock(gMtx);
        ... // do stuff
        // when lock goes out of scope, destructor releases the mutex
    }
   @endcode
 *
 * You can also explicitly release the mutex by calling RTCLock::release().
 * This might be helpful if the lock doesn't go out of scope early enough
 * for your mutex to be released.
 */
class RTCLock
{
private:
    /** Reference to the lock we're holding. */
    RTCLockMtx &m_rMtx;
    /** Whether we're currently holding the lock of if it was already
     *  explictily released by the release() method. */
    bool        m_fLocked;

public:
    RTCLock(RTCLockMtx &a_rMtx)
        : m_rMtx(a_rMtx)
    {
        m_rMtx.lock();
        m_fLocked = true;
    }

    ~RTCLock()
    {
        if (m_fLocked)
            m_rMtx.unlock();
    }

    inline void release()
    {
        if (m_fLocked)
        {
            m_rMtx.unlock();
            m_fLocked = false;
        }
    }
};


/** @} */

RT_C_DECLS_END

#endif /* !IPRT_INCLUDED_cpp_lock_h */