[WorldWind学习]8.Cache对象

MainApplication的构造函数599行实例化了worldWindow的Cache属性。

// set Upper and Lower limits for Cache size control, in bytes
                long CacheUpperLimit = (long)Settings.CacheSizeMegaBytes * 1024L * 1024L;
                long CacheLowerLimit = (long)Settings.CacheSizeMegaBytes * 768L * 1024L;    //75% of upper limit
                //Set up the cache
                worldWindow.Cache = new Cache(
                    Settings.CachePath,
                    CacheLowerLimit,
                    CacheUpperLimit,
                    Settings.CacheCleanupInterval, 
                    Settings.TotalRunTime );

这之前先看一下432行Settings的定义，

public static WorldWindSettings Settings = new WorldWindSettings();

在487~501行Main函数中可以看到通过LoadSettings()函数实现settings的赋值。

// ParseArgs may set values that are used elsewhere,
// such as startFullScreen and CurrentSettingsDirectory.
ParseArgs(args);
if(CurrentSettingsDirectory == null)
{
      // load program settings from default directory
      LoadSettings();    
      World.LoadSettings();
}
else
{
    LoadSettings(CurrentSettingsDirectory);
    World.LoadSettings(CurrentSettingsDirectory);
}

/// <summary>
        /// Deserializes and optionally decrypts settings
        /// </summary>
        private static void LoadSettings()
        {
            try
            {
                Settings = (WorldWindSettings) SettingsBase.Load(Settings, SettingsBase.LocationType.User);

                if(!File.Exists(Settings.FileName))
                {
                    Settings.PluginsLoadedOnStartup.Add("ShapeFileInfoTool");
                    //Settings.PluginsLoadedOnStartup.Add("OverviewFormLoader");
                    //Settings.PluginsLoadedOnStartup.Add("Atmosphere");
                    Settings.PluginsLoadedOnStartup.Add("SkyGradient");
                    Settings.PluginsLoadedOnStartup.Add("BmngLoader");
                    //Settings.PluginsLoadedOnStartup.Add("Compass");
                    //Settings.PluginsLoadedOnStartup.Add("ExternalLayerManagerLoader");
                    Settings.PluginsLoadedOnStartup.Add("MeasureTool");
                    //Settings.PluginsLoadedOnStartup.Add("MovieRecorder");
                    Settings.PluginsLoadedOnStartup.Add("NRLWeatherLoader");
                    Settings.PluginsLoadedOnStartup.Add("ShapeFileLoader");
                    Settings.PluginsLoadedOnStartup.Add("Stars3D");
                    Settings.PluginsLoadedOnStartup.Add("GlobalClouds");
                    Settings.PluginsLoadedOnStartup.Add("PlaceFinderLoader");
                    Settings.PluginsLoadedOnStartup.Add("LightController");

                    Settings.PluginsLoadedOnStartup.Add("Earthquake_2.0.2.1");
                    Settings.PluginsLoadedOnStartup.Add("Historical_Earthquake_2.0.2.2");
                    Settings.PluginsLoadedOnStartup.Add("KMLImporter");
                    //Settings.PluginsLoadedOnStartup.Add("doublezoom");
                    //Settings.PluginsLoadedOnStartup.Add("PlanetaryRings");
                    Settings.PluginsLoadedOnStartup.Add("TimeController");
                    //Settings.PluginsLoadedOnStartup.Add("WavingFlags");
                    Settings.PluginsLoadedOnStartup.Add("ScaleBarLegend");
                    Settings.PluginsLoadedOnStartup.Add("Compass3D");
                    Settings.PluginsLoadedOnStartup.Add("AnaglyphStereo");
                    Settings.PluginsLoadedOnStartup.Add("GlobeIcon");

                }
                // decrypt encoded user credentials
                DataProtector dp = new DataProtector(DataProtector.Store.USE_USER_STORE);

                if(Settings.ProxyUsername.Length > 0) Settings.ProxyUsername = dp.TransparentDecrypt(Settings.ProxyUsername);
                if(Settings.ProxyPassword.Length > 0) Settings.ProxyPassword = dp.TransparentDecrypt(Settings.ProxyPassword);
            }
            catch(Exception caught)
            {
                Log.Write(caught);
            }
        }

Settings = (WorldWindSettings) SettingsBase.Load(Settings, SettingsBase.LocationType.User);这句代码需要详细查看， SettingsBase.LocationType.User

public static string DefaultLocation(LocationType locationType)
        {
            string directory;

            switch(locationType) 
            {
                case LocationType.UserLocal:
                    // Example: @"C:\Documents and Settings\<user>\Local Settings\Application Data\NASA\NASA World Wind\1.3.3.11250"
                    return Application.LocalUserAppDataPath;
                
                case LocationType.UserCommon:
                    // Example: @"C:\Documents and Settings\All Users\Application Data\NASA\NASA World Wind\1.3.3.11250"
                    return Application.CommonAppDataPath;
                
                case LocationType.Application:
                    // Example: @"C:\Program Files\NASA\World Wind\"
                    return Application.StartupPath;

                default:
                    // fall through to regular (roaming) user
                case LocationType.User:   
                    // Example: @"C:\Documents and Settings\<user>\Application Data\NASA\World Wind\1.3.3"
                    directory = Log.DefaultSettingsDirectory();
                    Directory.CreateDirectory(directory);
                    return directory;
            }
        }

设置断点会发现directory的路径为：‘C:\Users\yangfan\AppData\Roaming\NASA\World Wind\1.4.0.0’，进入一看，原来是日志文件和World、WorldWind配置文件。

我还以为是影像或者矢量数据的缓存呢！

SettingsBase利用XmlSerializer实现配置文件保存。

MainApplication中只有开始介绍的一句实例化了worldWindow的Cache属性，而WorldWindow类中也只有private Cache m_Cache;属性定义。

注意到Cache类中定义了对象：Timer m_timer;

/// <summary>
        /// Initializes a new instance of the <see cref= "T:WorldWind.Cache"/> class.
        /// </summary>
        /// <param name="cacheDirectory">Location of the cache files.</param>
        /// <param name="cleanupFrequencyInterval">Frequency of cache cleanup.</param>
        /// <param name="totalRunTime">Total duration application has been running so far.</param>
        public Cache(
            string cacheDirectory,
            TimeSpan cleanupFrequencyInterval,
            TimeSpan totalRunTime)
        {
            this.CleanupFrequency = cleanupFrequencyInterval;
            this.CacheDirectory = cacheDirectory;
            Directory.CreateDirectory(this.CacheDirectory);

            // Start the timer
            double firstDueSeconds = cleanupFrequencyInterval.TotalSeconds - 
                totalRunTime.TotalSeconds % cleanupFrequencyInterval.TotalSeconds;
19             m_timer = new Timer( new TimerCallback(OnTimer), null,
20                 (long)(firstDueSeconds*1000),
21                 (long)cleanupFrequencyInterval.TotalMilliseconds );
        }

        /// <summary>
        /// Constructor.
        /// </summary>
        /// <param name="cacheDirectory">Location of the cache files.</param>
        /// <param name="cleanupFrequencyInterval">Frequency of cache cleanup.</param>
        /// <param name="totalRunTime">Total duration application has been running so far.</param>
        public Cache(
            string cacheDirectory,
            long cacheLowerLimit,
            long cacheUpperLimit,
            TimeSpan cleanupFrequencyInterval,
            TimeSpan totalRunTime)
            : this(cacheDirectory, cleanupFrequencyInterval, totalRunTime )
        {
            this.CacheLowerLimit = cacheLowerLimit;
            this.CacheUpperLimit = cacheUpperLimit;
        }

延迟后，每间隔cleanupFrequencyInterval.TotalMilliseconds调用OnTimer方法执行清理。

/// <summary>
        /// Monitors the cache, makes sure it stays within limits.
        /// </summary>
        private void OnTimer(object state)
        {
            try
            {
                // We are are not in a hurry
                Thread.CurrentThread.Priority = ThreadPriority.BelowNormal;

                // dirSize is reported as the total of the file sizes, in bytes
                // TODO: use the on-disk filesize, not FileInfo.Length, to calculate dirSize
                long dirSize = GetDirectorySize(new DirectoryInfo(this.CacheDirectory));//dirSize是缓存文件夹的大小
                if(dirSize < this.CacheUpperLimit)//小于限定值不清理
                    return;

                ArrayList fileInfoList = GetDirectoryFileInfoList(new DirectoryInfo(this.CacheDirectory));
                while(dirSize > this.CacheLowerLimit)
                {
                    if (fileInfoList.Count <= 100)
                        break;

                    FileInfo oldestFile = null;
                    foreach(FileInfo curFile in fileInfoList)
                    {
                        if(oldestFile == null)
                        {
                            oldestFile = curFile;
                            continue;
                        }

                        if(curFile.LastAccessTimeUtc < oldestFile.LastAccessTimeUtc)
                        {
                            oldestFile = curFile;
                        }
                    }

                    fileInfoList.Remove(oldestFile);
                    dirSize -= oldestFile.Length;
                    try
                    {
                        File.Delete(oldestFile.FullName);

                        // Recursively remove empty directories
                        string directory = oldestFile.Directory.FullName;
                        while(Directory.GetFileSystemEntries(directory).Length==0)
                        {
                            Directory.Delete(directory);
                            directory = Path.GetDirectoryName(directory);
                        }
                    }
                    catch(IOException)
                    {
                        // Ignore non-removable file - move on to next
                    }
                }
            }
            catch(Exception caught)
            {
                Log.Write(Log.Levels.Error, "CACH", caught.Message);
            }
        }

计算缓存文件夹大小：

public static long GetDirectorySize(DirectoryInfo inDir)
        {
            long returnBytes = 0;
            foreach(DirectoryInfo subDir in inDir.GetDirectories())
            {
                returnBytes += GetDirectorySize(subDir);
            }
            foreach(FileInfo fi in inDir.GetFiles())
            {
                try
                {
                    returnBytes += fi.Length;
                } 
                catch(System.IO.IOException)
                {
                    // Ignore files that may have disappeared since we started scanning.
                }
            }
            return returnBytes;
        }