JUCE/modules/juce_core/threads/juce_SpinLock.h

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

   This file is part of the juce_core module of the JUCE library.
   Copyright (c) 2013 - Raw Material Software Ltd.

   Permission to use, copy, modify, and/or distribute this software for any purpose with
   or without fee is hereby granted, provided that the above copyright notice and this
   permission notice appear in all copies.

   THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES WITH REGARD
   TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS. IN
   NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL
   DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER
   IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
   CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.

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

   NOTE! This permissive ISC license applies ONLY to files within the juce_core module!
   All other JUCE modules are covered by a dual GPL/commercial license, so if you are
   using any other modules, be sure to check that you also comply with their license.

   For more details, visit www.juce.com

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

#ifndef JUCE_SPINLOCK_H_INCLUDED
#define JUCE_SPINLOCK_H_INCLUDED


//==============================================================================
/**
    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_H_INCLUDED