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TMessagesProj/jni/voip/webrtc/base/metrics/bucket_ranges.h

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+// Copyright (c) 2012 The Chromium Authors. All rights reserved.
+// 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 <stddef.h>
+#include <stdint.h>
+
+#include <vector>
+
+#include <limits.h>
+
+#include "base/atomicops.h"
+#include "base/base_export.h"
+#include "base/macros.h"
+#include "base/metrics/histogram_base.h"
+
+namespace base {
+
+class BASE_EXPORT BucketRanges {
+ public:
+  typedef std::vector<HistogramBase::Sample> Ranges;
+
+  explicit BucketRanges(size_t num_ranges);
+  ~BucketRanges();
+
+  size_t size() const { return ranges_.size(); }
+  HistogramBase::Sample range(size_t i) const { return ranges_[i]; }
+  void set_range(size_t i, HistogramBase::Sample 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 {
+    subtle::Release_Store(&persistent_reference_, ref);
+  }
+  uint32_t persistent_reference() const {
+    return subtle::Acquire_Load(&persistent_reference_);
+  }
+
+ 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 subtle::Atomic32 persistent_reference_ = 0;
+
+  DISALLOW_COPY_AND_ASSIGN(BucketRanges);
+};
+
+}  // namespace base
+
+#endif  // BASE_METRICS_BUCKET_RANGES_H_