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// <ORIGINAL-AUTHOR>: Greg Lueck
// <COMPONENT>: sync
// <FILE-TYPE>: component private header

#ifndef SYNC_BACKOFF_OR_YIELD_HPP
#define SYNC_BACKOFF_OR_YIELD_HPP

#include "atomic.hpp"


namespace SYNC {


/*!
 * This utility can be used to implement the delay in the body of a spin-wait
 * loop.  Initial iterations of the delay use an exponential backoff that
 * actively spins on the CPU.  However, after a limit is reached, each delay
 * iteration makes an O/S call to yield the processor.
 *
 * @tparam OS               Type which provides O/S primitives.  See
 *                           \ref SYNC_OS.  The \a OS type must define the
 *                           Yield() method.
 * @tparam BACKOFF_LIMIT    The iteration limit, after which each delay
 *                           makes a call to Yield().  Since each iteration is
 *                           exponential, the total delay before doing a
 *                           Yield() is proportional to 2^BACKOFF_LIMIT.
 */
template<typename OS, unsigned BACKOFF_LIMIT> class /*<UTILITY>*/ BACKOFF_OR_YIELD
{
public:
    BACKOFF_OR_YIELD() : _backoff(0) {}

    void Delay()
    {
        if (_backoff.GetIterationCount() < BACKOFF_LIMIT)
            _backoff.Delay();
        else
            OS::Yield();
    }

private:
    ATOMIC::EXPONENTIAL_BACKOFF<> _backoff;
};

} // namespace
#endif // file guard
