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// Copyright 2012 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
//
// BucketRanges stores the vector of ranges that delimit what samples are
// tallied in the corresponding buckets of a histogram. Histograms that have
// same ranges for all their corresponding buckets should share the same
// BucketRanges object.
//
// E.g. A 5 buckets LinearHistogram with 1 as minimal value and 4 as maximal
// value will need a BucketRanges with 6 ranges:
// 0, 1, 2, 3, 4, INT_MAX
//
// TODO(kaiwang): Currently we keep all negative values in 0~1 bucket. Consider
// changing 0 to INT_MIN.
#ifndef BASE_METRICS_BUCKET_RANGES_H_
#define BASE_METRICS_BUCKET_RANGES_H_
#include <limits.h>
#include <stddef.h>
#include <stdint.h>
#include <atomic>
#include <vector>
#include "base/base_export.h"
#include "base/check_op.h"
#include "base/containers/span.h"
#include "base/metrics/histogram_base.h"
namespace base {
class BASE_EXPORT BucketRanges {
public:
typedef std::vector<HistogramBase::Sample32> Ranges;
explicit BucketRanges(size_t num_ranges);
explicit BucketRanges(base::span<const HistogramBase::Sample32> data);
BucketRanges(const BucketRanges&) = delete;
BucketRanges& operator=(const BucketRanges&) = delete;
~BucketRanges();
size_t size() const { return ranges_.size(); }
HistogramBase::Sample32 range(size_t i) const { return ranges_[i]; }
void set_range(size_t i, HistogramBase::Sample32 value) {
DCHECK_LT(i, ranges_.size());
DCHECK_GE(value, 0);
ranges_[i] = value;
}
uint32_t checksum() const { return checksum_; }
void set_checksum(uint32_t checksum) { checksum_ = checksum; }
// A bucket is defined by a consecutive pair of entries in |ranges|, so there
// is one fewer bucket than there are ranges. For example, if |ranges| is
// [0, 1, 3, 7, INT_MAX], then the buckets in this histogram are
// [0, 1), [1, 3), [3, 7), and [7, INT_MAX).
size_t bucket_count() const { return ranges_.size() - 1; }
// Checksum methods to verify whether the ranges are corrupted (e.g. bad
// memory access).
uint32_t CalculateChecksum() const;
bool HasValidChecksum() const;
void ResetChecksum();
// Return true iff |other| object has same ranges_ as |this| object's ranges_.
bool Equals(const BucketRanges* other) const;
// Set and get a reference into persistent memory where this bucket data
// can be found (and re-used). These calls are internally atomic with no
// safety against overwriting an existing value since though it is wasteful
// to have multiple identical persistent records, it is still safe.
void set_persistent_reference(uint32_t ref) const {
persistent_reference_.store(ref, std::memory_order_release);
}
uint32_t persistent_reference() const {
return persistent_reference_.load(std::memory_order_acquire);
}
private:
// A monotonically increasing list of values which determine which bucket to
// put a sample into. For each index, show the smallest sample that can be
// added to the corresponding bucket.
Ranges ranges_;
// Checksum for the conntents of ranges_. Used to detect random over-writes
// of our data, and to quickly see if some other BucketRanges instance is
// possibly Equal() to this instance.
// TODO(kaiwang): Consider change this to uint64_t. Because we see a lot of
// noise on UMA dashboard.
uint32_t checksum_;
// A reference into a global PersistentMemoryAllocator where the ranges
// information is stored. This allows for the record to be created once and
// re-used simply by having all histograms with the same ranges use the
// same reference.
mutable std::atomic<uint32_t> persistent_reference_{0};
};
} // namespace base
#endif // BASE_METRICS_BUCKET_RANGES_H_
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