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106 lines
3.7 KiB
C++
106 lines
3.7 KiB
C++
// Copyright (c) 2012 The Chromium Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style license that can be
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// found in the LICENSE file.
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//
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// BucketRanges stores the vector of ranges that delimit what samples are
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// tallied in the corresponding buckets of a histogram. Histograms that have
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// same ranges for all their corresponding buckets should share the same
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// BucketRanges object.
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//
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// E.g. A 5 buckets LinearHistogram with 1 as minimal value and 4 as maximal
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// value will need a BucketRanges with 6 ranges:
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// 0, 1, 2, 3, 4, INT_MAX
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//
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// TODO(kaiwang): Currently we keep all negative values in 0~1 bucket. Consider
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// changing 0 to INT_MIN.
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#ifndef BASE_METRICS_BUCKET_RANGES_H_
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#define BASE_METRICS_BUCKET_RANGES_H_
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#include <stddef.h>
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#include <stdint.h>
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#include <vector>
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#include <limits.h>
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#include "base/atomicops.h"
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#include "base/base_export.h"
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#include "base/macros.h"
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#include "base/metrics/histogram_base.h"
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namespace base {
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class BASE_EXPORT BucketRanges {
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public:
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typedef std::vector<HistogramBase::Sample> Ranges;
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explicit BucketRanges(size_t num_ranges);
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~BucketRanges();
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size_t size() const { return ranges_.size(); }
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HistogramBase::Sample range(size_t i) const { return ranges_[i]; }
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void set_range(size_t i, HistogramBase::Sample value) {
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DCHECK_LT(i, ranges_.size());
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DCHECK_GE(value, 0);
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ranges_[i] = value;
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}
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uint32_t checksum() const { return checksum_; }
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void set_checksum(uint32_t checksum) { checksum_ = checksum; }
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// A bucket is defined by a consecutive pair of entries in |ranges|, so there
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// is one fewer bucket than there are ranges. For example, if |ranges| is
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// [0, 1, 3, 7, INT_MAX], then the buckets in this histogram are
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// [0, 1), [1, 3), [3, 7), and [7, INT_MAX).
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size_t bucket_count() const { return ranges_.size() - 1; }
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// Checksum methods to verify whether the ranges are corrupted (e.g. bad
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// memory access).
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uint32_t CalculateChecksum() const;
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bool HasValidChecksum() const;
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void ResetChecksum();
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// Return true iff |other| object has same ranges_ as |this| object's ranges_.
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bool Equals(const BucketRanges* other) const;
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// Set and get a reference into persistent memory where this bucket data
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// can be found (and re-used). These calls are internally atomic with no
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// safety against overwriting an existing value since though it is wasteful
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// to have multiple identical persistent records, it is still safe.
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void set_persistent_reference(uint32_t ref) const {
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subtle::Release_Store(&persistent_reference_, ref);
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}
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uint32_t persistent_reference() const {
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return subtle::Acquire_Load(&persistent_reference_);
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}
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private:
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// A monotonically increasing list of values which determine which bucket to
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// put a sample into. For each index, show the smallest sample that can be
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// added to the corresponding bucket.
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Ranges ranges_;
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// Checksum for the conntents of ranges_. Used to detect random over-writes
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// of our data, and to quickly see if some other BucketRanges instance is
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// possibly Equal() to this instance.
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// TODO(kaiwang): Consider change this to uint64_t. Because we see a lot of
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// noise on UMA dashboard.
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uint32_t checksum_;
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// A reference into a global PersistentMemoryAllocator where the ranges
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// information is stored. This allows for the record to be created once and
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// re-used simply by having all histograms with the same ranges use the
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// same reference.
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mutable subtle::Atomic32 persistent_reference_ = 0;
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DISALLOW_COPY_AND_ASSIGN(BucketRanges);
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};
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//////////////////////////////////////////////////////////////////////////////
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// Expose only for test.
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BASE_EXPORT extern const uint32_t kCrcTable[256];
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} // namespace base
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#endif // BASE_METRICS_BUCKET_RANGES_H_
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