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/*
* Copyright (C) 2008-2017 Apple Inc. All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
*
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
* 3. Neither the name of Apple Inc. ("Apple") nor the names of
* its contributors may be used to endorse or promote products derived
* from this software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY APPLE AND ITS CONTRIBUTORS "AS IS" AND ANY
* EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
* WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
* DISCLAIMED. IN NO EVENT SHALL APPLE OR ITS CONTRIBUTORS BE LIABLE FOR ANY
* DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
* (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
* LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
* ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
* THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
#ifndef Locker_h
#define Locker_h
#include <wtf/Assertions.h>
#include <wtf/Atomics.h>
#include <wtf/Noncopyable.h>
namespace WTF {
enum NoLockingNecessaryTag { NoLockingNecessary };
class AbstractLocker {
WTF_MAKE_NONCOPYABLE(AbstractLocker);
public:
AbstractLocker(NoLockingNecessaryTag)
{
}
protected:
AbstractLocker()
{
}
};
template <typename T> class Locker : public AbstractLocker {
public:
explicit Locker(T& lockable) : m_lockable(&lockable) { lock(); }
explicit Locker(T* lockable) : m_lockable(lockable) { lock(); }
// You should be wary of using this constructor. It's only applicable
// in places where there is a locking protocol for a particular object
// but it's not necessary to engage in that protocol yet. For example,
// this often happens when an object is newly allocated and it can not
// be accessed concurrently.
Locker(NoLockingNecessaryTag) : m_lockable(nullptr) { }
Locker(int) = delete;
~Locker()
{
compilerFence();
if (m_lockable)
m_lockable->unlock();
}
static Locker tryLock(T& lockable)
{
Locker result(NoLockingNecessary);
if (lockable.tryLock()) {
result.m_lockable = &lockable;
return result;
}
return result;
}
explicit operator bool() const { return !!m_lockable; }
void unlockEarly()
{
m_lockable->unlock();
m_lockable = 0;
}
// It's great to be able to pass lockers around. It enables custom locking adaptors like
// JSC::LockDuringMarking.
Locker(Locker&& other)
: m_lockable(other.m_lockable)
{
other.m_lockable = nullptr;
}
Locker& operator=(Locker&& other)
{
if (m_lockable)
m_lockable->unlock();
m_lockable = other.m_lockable;
other.m_lockable = nullptr;
return *this;
}
private:
void lock()
{
if (m_lockable)
m_lockable->lock();
compilerFence();
}
T* m_lockable;
};
// Use this lock scope like so:
// auto locker = holdLock(lock);
template<typename LockType>
Locker<LockType> holdLock(LockType& lock)
{
return Locker<LockType>(lock);
}
template<typename LockType>
Locker<LockType> holdLockIf(LockType& lock, bool predicate)
{
return Locker<LockType>(predicate ? &lock : nullptr);
}
template<typename LockType>
Locker<LockType> tryHoldLock(LockType& lock)
{
return Locker<LockType>::tryLock(lock);
}
}
using WTF::AbstractLocker;
using WTF::Locker;
using WTF::NoLockingNecessaryTag;
using WTF::NoLockingNecessary;
using WTF::holdLock;
using WTF::holdLockIf;
#endif