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// Copyright Yahoo. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
#pragma once
#include <vespa/document/bucket/bucketid.h>
#include <atomic>
namespace storage {
/**
* Utility class for keeping track of the lowest used bits count seen
* across a set of buckets.
*
* Thread safe for reads and writes.
*/
class MinimumUsedBitsTracker
{
std::atomic<uint32_t> _min_used_bits;
public:
constexpr MinimumUsedBitsTracker() noexcept
: _min_used_bits(58)
{}
/**
* Returns true iff new bucket led to a decrease in the used bits count.
*/
bool update(const document::BucketId& bucket) noexcept {
const uint32_t bucket_bits = bucket.getUsedBits();
uint32_t current_bits = _min_used_bits.load(std::memory_order_relaxed);
if (bucket_bits < current_bits) {
while (!_min_used_bits.compare_exchange_strong(current_bits, bucket_bits,
std::memory_order_relaxed,
std::memory_order_relaxed))
{
if (bucket_bits >= current_bits) {
return false; // We've raced with another writer that had lower or equal bits to our own bucket.
}
}
return true;
}
return false;
}
[[nodiscard]] uint32_t getMinUsedBits() const noexcept {
return _min_used_bits.load(std::memory_order_relaxed);
}
void setMinUsedBits(uint32_t minUsedBits) noexcept {
_min_used_bits.store(minUsedBits, std::memory_order_relaxed);
}
};
}
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