/*
 * Copyright (C) 2011 Google 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:
 *
 *     * Redistributions of source code must retain the above copyright
 * notice, this list of conditions and the following disclaimer.
 *     * 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.
 *     * Neither the name of Google Inc. 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 THE COPYRIGHT HOLDERS AND 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 THE COPYRIGHT
 * OWNER OR 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 ThreadRestrictionVerifier_h
#define ThreadRestrictionVerifier_h

#include "wtf/Assertions.h"

#if ENABLE(ASSERT)

#include "wtf/Threading.h"

namespace WTF {

// Verifies that a class is used in a way that respects its lack of thread-safety.
// The default mode is to verify that the object will only be used on a single thread. The
// thread gets captured when setShared(true) is called.
// The mode may be changed by calling useMutexMode (or turnOffVerification).
class ThreadRestrictionVerifier {
public:
    ThreadRestrictionVerifier()
        : m_shared(false)
        , m_owningThread(0)
    {
    }

    void checkSafeToUse() const
    {
        // If this assert fires, it either indicates a thread safety issue or
        // that the verification needs to change.
        ASSERT_WITH_SECURITY_IMPLICATION(isSafeToUse());
    }

    // Call onRef() before refCount is incremented in ref().
    void onRef(int refCount)
    {
        // Start thread verification as soon as the ref count gets to 2. This
        // heuristic reflects the fact that items are often created on one
        // thread and then given to another thread to be used.
        // FIXME: Make this restriction tigher. Especially as we move to more
        // common methods for sharing items across threads like
        // CrossThreadCopier.h
        // We should be able to add a "detachFromThread" method to make this
        // explicit.
        if (refCount == 1)
            setShared(true);
        checkSafeToUse();
    }

    // Call onDeref() before refCount is decremented in deref().
    void onDeref(int refCount)
    {
        checkSafeToUse();

        // Stop thread verification when the ref goes to 1 because it
        // is safe to be passed to another thread at this point.
        if (refCount == 2)
            setShared(false);
    }

private:
    // Indicates that the object may (or may not) be owned by more than one place.
    void setShared(bool shared)
    {
        bool previouslyShared = m_shared;
        m_shared = shared;

        if (!m_shared)
            return;

        ASSERT_UNUSED(previouslyShared, shared != previouslyShared);
        // Capture the current thread to verify that subsequent ref/deref happen on this thread.
        m_owningThread = currentThread();
    }

    // Is it OK to use the object at this moment on the current thread?
    bool isSafeToUse() const
    {
        if (!m_shared)
            return true;

        return m_owningThread == currentThread();
    }

    bool m_shared;

    ThreadIdentifier m_owningThread;
};

} // namespace WTF

#endif // ENABLE(ASSERT)
#endif // ThreadRestrictionVerifier_h