chromium之histogram.h

histogram不知道是干啥的

// Histogram is an object that aggregates statistics, and can summarize them in
// various forms, including ASCII graphical, HTML, and numerically (as a
// vector of numbers corresponding to each of the aggregating buckets).

google翻译

//直方图是汇总统计信息的对象，可以将它们汇总
//各种形式，包括ASCII图形，HTML和数字（如
//每个聚合桶对应的数字向量）。

直方图——不就是统计用的，PPT还有饼图什么的

不管了，看看怎么实现的，就知道是干嘛用的了。

瞄一下，有没有引用不认识的头文件

histogram.cc

#include "base/histogram.h"#include <math.h>
#include <string>#include "base/logging.h"
#include "base/pickle.h"
#include "base/string_util.h"

有一个！

#include "base/pickle.h"

参见分析chromium之pickle，我们知道该类提供基本的二进制打包、解包的功能。这样代码就能继续看下去了

这个pickle在头文件里有用到

    bool Serialize(Pickle* pickle) const;bool Deserialize(void** iter, const Pickle& pickle);

序列化一般是进程间通讯传递数据用的

序列化在什么时候用：

当你想把的内存中的对象状态保存到一个文件中或者数据库中时候；
当你想用套接字在网络上传送对象的时候；
当你想通过RMI传输对象的时候；

一个类，有没有掌握——给你头文件，你会不会使用里面的函数——会了，这个类你就懂了。

class Pickle;class Histogram {public:
//----------------------------------------------------------------------------// Statistic values, developed over the life of the histogram.class SampleSet {public:explicit SampleSet();// Adjust size of counts_ for use with given histogram.void Resize(const Histogram& histogram);void CheckSize(const Histogram& histogram) const;// Accessor for histogram to make routine additions.void Accumulate(Sample value, Count count, size_t index);// Accessor methods.Count counts(size_t i) const { return counts_[i]; }Count TotalCount() const;int64 sum() const { return sum_; }int64 square_sum() const { return square_sum_; }// Arithmetic manipulation of corresponding elements of the set.void Add(const SampleSet& other);void Subtract(const SampleSet& other);bool Serialize(Pickle* pickle) const;bool Deserialize(void** iter, const Pickle& pickle);protected:// Actual histogram data is stored in buckets, showing the count of values// that fit into each bucket.
    Counts counts_;// Save simple stats locally.  Note that this MIGHT get done in base class// without shared memory at some point.int64 sum_;         // sum of samples.int64 square_sum_;  // sum of squares of samples.
  };//----------------------------------------------------------------------------
Histogram(const char* name, Sample minimum,Sample maximum, size_t bucket_count);Histogram(const char* name, base::TimeDelta minimum,base::TimeDelta maximum, size_t bucket_count);virtual ~Histogram();void Add(int value);// Accept a TimeDelta to increment.void AddTime(base::TimeDelta time) {Add(static_cast<int>(time.InMilliseconds()));}void AddSampleSet(const SampleSet& sample);// The following methods provide graphical histogram displays.void WriteHTMLGraph(std::string* output) const;void WriteAscii(bool graph_it, const std::string& newline,std::string* output) const;// Support generic flagging of Histograms.// 0x1 Currently used to mark this histogram to be recorded by UMA..// 0x8000 means print ranges in hex.void SetFlags(int flags) { flags_ |= flags; }void ClearFlags(int flags) { flags_ &= ~flags; }int flags() const { return flags_; }virtual BucketLayout histogram_type() const { return EXPONENTIAL; }// Convenience methods for serializing/deserializing the histograms.// Histograms from Renderer process are serialized and sent to the browser.// Browser process reconstructs the histogram from the pickled version// accumulates the browser-side shadow copy of histograms (that mirror// histograms created in the renderer).// Serialize the given snapshot of a Histogram into a String. Uses// Pickle class to flatten the object.static std::string SerializeHistogramInfo(const Histogram& histogram,const SampleSet& snapshot);// The following method accepts a list of pickled histograms and// builds a histogram and updates shadow copy of histogram data in the// browser process.static bool DeserializeHistogramInfo(const std::string& histogram_info);//----------------------------------------------------------------------------// Accessors for serialization and testing.//----------------------------------------------------------------------------const std::string histogram_name() const { return histogram_name_; }Sample declared_min() const { return declared_min_; }Sample declared_max() const { return declared_max_; }virtual Sample ranges(size_t i) const { return ranges_[i];}virtual size_t bucket_count() const { return bucket_count_; }// Snapshot the current complete set of sample data.// Override with atomic/locked snapshot if needed.virtual void SnapshotSample(SampleSet* sample) const;// ...
}

看一下测试用例

// Check for basic syntax and use.
TEST(HistogramTest, StartupShutdownTest) {// Try basic constructionHistogram histogram("TestHistogram", 1, 1000, 10);Histogram histogram1("Test1Histogram", 1, 1000, 10);LinearHistogram linear_histogram("TestLinearHistogram", 1, 1000, 10);LinearHistogram linear_histogram1("Test1LinearHistogram", 1, 1000, 10);// Use standard macros (but with fixed samples)HISTOGRAM_TIMES("Test2Histogram", TimeDelta::FromDays(1));HISTOGRAM_COUNTS("Test3Histogram", 30);DHISTOGRAM_TIMES("Test4Histogram", TimeDelta::FromDays(1));DHISTOGRAM_COUNTS("Test5Histogram", 30);ASSET_HISTOGRAM_COUNTS("Test6Histogram", 129);// Try to construct samples.
  Histogram::SampleSet sample1;Histogram::SampleSet sample2;// Use copy constructor of SampleSetsample1 = sample2;Histogram::SampleSet sample3(sample1);// Finally test a statistics recorder, without really using it.
  StatisticsRecorder recorder;
}