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// Copyright 2017 Yahoo Holdings. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
/**
* \class storage::framework::ReduceMemoryUsageInterface
* \ingroup memory
*
* \brief The manager can take memory back when needed using this interface.
*
* Some memory users, typically caches, wants to use all available memory. But
* to let them use all available memory, it must also be easy to take memory
* back when needed for something else. An implementation of this interface can
* be given on memory allocations to give the memory manager the ability to take
* memory back when needed.
*/
#pragma once
namespace storage::framework {
struct ReduceMemoryUsageInterface
{
virtual ~ReduceMemoryUsageInterface() {}
/**
* This callback is called when the memory manager want to reduce the usage
* of the given memory token. Actual memory to be released should be
* released in this function. The token itself will be adjusted by the
* memory manager though. The memory manager may keep a lock through this
* call, so no memory manager calls should be made inside this callback.
*
* It is recommended that you actually release at least as many bytes as
* requested. Though currently it is allowed to reduce less or refuse, but
* this might mean that some higher priority task does not get the memory it
* needs.
*
* @param reduceBy Always in the range 0 < reduceBy <= token.size()
* @return The amount of memory no longer used.
*/
virtual uint64_t reduceMemoryConsumption(const MemoryToken&, uint64_t reduceBy) = 0;
};
}
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