/**
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 * KIND, either express or implied.  See the License for the
 * specific language governing permissions and limitations
 * under the License.
 */
#ifndef ParallelVectorIterator_h
#define ParallelVectorIterator_h

#include <wtf/FastMalloc.h>
#include <wtf/Lock.h>
#include <wtf/Noncopyable.h>

namespace WTF {

template<typename VectorType>
class ParallelVectorIterator {
    WTF_MAKE_NONCOPYABLE(ParallelVectorIterator);
    WTF_MAKE_FAST_ALLOCATED;
public:
    ParallelVectorIterator(VectorType& vector, size_t shardSize)
        : m_vector(vector)
        , m_shardSize(shardSize)
    {
    }

    template<typename Functor>
    ALWAYS_INLINE void iterate(const Functor& functor)
    {
        for (;;) {
            size_t begin;
            size_t end;
            {
                LockHolder locker(m_lock);
                begin = m_next;
                if (begin == m_vector.size())
                    return;
                if (m_vector.size() - begin < m_shardSize)
                    end = m_vector.size();
                else
                    end = begin + m_shardSize;
                RELEASE_ASSERT(end <= m_vector.size());
                RELEASE_ASSERT(begin < end);
                m_next = end;
            }

            for (size_t i = begin; i < end; ++i)
                functor(m_vector[i]);
        }
    }
private:
    VectorType& m_vector;
    Lock m_lock;
    size_t m_shardSize;
    size_t m_next { 0 };
};

} // namespace WTF

using WTF::ParallelVectorIterator;

#endif // ParallelVectorIterator_h