JUCE/modules/juce_core/threads/juce_SpinLock.h

/*
  ==============================================================================

   This file is part of the JUCE library - "Jules' Utility Class Extensions"
   Copyright 2004-11 by Raw Material Software Ltd.

  ------------------------------------------------------------------------------

   JUCE can be redistributed and/or modified under the terms of the GNU General
   Public License (Version 2), as published by the Free Software Foundation.
   A copy of the license is included in the JUCE distribution, or can be found
   online at www.gnu.org/licenses.

   JUCE 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.

  ------------------------------------------------------------------------------

   To release a closed-source product which uses JUCE, commercial licenses are
   available: visit www.rawmaterialsoftware.com/juce for more information.

  ==============================================================================
*/

#ifndef __JUCE_SPINLOCK_JUCEHEADER__
#define __JUCE_SPINLOCK_JUCEHEADER__

#include "juce_ScopedLock.h"


//==============================================================================
/**
    A simple spin-lock class that can be used as a simple, low-overhead mutex for
    uncontended situations.

    Note that unlike a CriticalSection, this type of lock is not re-entrant, and may
    be less efficient when used it a highly contended situation, but it's very small and
    requires almost no initialisation.
    It's most appropriate for simple situations where you're only going to hold the
    lock for a very brief time.

    @see CriticalSection
*/
class JUCE_API  SpinLock
{
public:
    inline SpinLock() noexcept {}
    inline ~SpinLock() noexcept {}

    /** Acquires the lock.
        This will block until the lock has been successfully acquired by this thread.
        Note that a SpinLock is NOT re-entrant, and is not smart enough to know whether the
        caller thread already has the lock - so if a thread tries to acquire a lock that it
        already holds, this method will never return!

        It's strongly recommended that you never call this method directly - instead use the
        ScopedLockType class to manage the locking using an RAII pattern instead.
    */
    void enter() const noexcept;

    /** Attempts to acquire the lock, returning true if this was successful. */
    inline bool tryEnter() const noexcept
    {
        return lock.compareAndSetBool (1, 0);
    }

    /** Releases the lock. */
    inline void exit() const noexcept
    {
        jassert (lock.value == 1); // Agh! Releasing a lock that isn't currently held!
        lock = 0;
    }

    //==============================================================================
    /** Provides the type of scoped lock to use for locking a SpinLock. */
    typedef GenericScopedLock <SpinLock>       ScopedLockType;

    /** Provides the type of scoped unlocker to use with a SpinLock. */
    typedef GenericScopedUnlock <SpinLock>     ScopedUnlockType;

private:
    //==============================================================================
    mutable Atomic<int> lock;

    JUCE_DECLARE_NON_COPYABLE (SpinLock);
};


#endif   // __JUCE_SPINLOCK_JUCEHEADER__