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Queues are useful for storing messages in the order they were received for sequential processing. Objects stored in a Queue<T> are inserted at one end and removed from the other. References: http://msdn.microsoft.com/en-us/library/7977ey2c.aspx

SqlConnection.Open - Opens a database connection with the property settings specified by the ConnectionString. SqlDataReader.Read - Advances the SqlDataReader to the next record. References:http://msdn.microsoft.com/en-us/library/system.data.sqlclient.sqlconnection.open.aspxhttp://msdn.microsoft.com/en-us/library/system.data.sqlclient.sqldatareader.read.aspx

You use #define to define a symbol. When you use the symbol as the expression that's passed to the #if directive, the expression will evaluate to true. Example:#define DEBUG      using System;      public class TestDefine   {       static void Main()       {   #if (DEBUG)           Console.WriteLine("Debugging is enabled.");   #endif   Reference:https://docs.microsoft.com/en-us/dotnet/csharp/language-reference/preprocessor-directives/preprocessor-define

FileMode.OpenOrCreate - Specifies that the operating system should open a file if it exists; otherwise, a new file should be created. If the file is opened with FileAccess.Read, FileIOPermissionAccess.Read permission is required. If the file access is FileAccess.Write, FileIOPermissionAccess.Write permission is required. If the file is opened with FileAccess.ReadWrite, both FileIOPermissionAccess.Read and FileIOPermissionAccess.Write permissions are required. FileShare.ReadWrite - Allows subsequent opening of the file for reading or writing. If this flag is not specified, any request to open the file for reading or writing (by this process or another process) will fail until the file is closed. However, even if this flag is specified, additional permissions might still be needed to access the file. References: http://msdn.microsoft.com/pl-pl/library/system.io.fileshare.aspxhttp://msdn.microsoft.com/en-us/library/system.io.filemode.aspx

JavaScriptSerializer.Deserialize<T> - Converts the specified JSON string to an object of type T. References: http://msdn.microsoft.com/en-us/library/bb355316.aspx

The DataContractJsonSerializer class serializes objects to the JavaScript Object Notation (JSON) and deserializes JSON data to objects. Use the DataContractJsonSerializer class to serialize instances of a type into a JSON document and to deserialize a JSON document into an instance of a type.

Sealed - When applied to a class, the sealed modifier prevents other classes from inheriting from it. References: http://msdn.microsoft.com/en-us/library/88c54tsw(v=vs.110).aspx

A String object concatenation operation always creates a new object from the existing string and the new data. A StringBuilder object maintains a buffer to accommodate the concatenation of new data. New data is appended to the buffer if room is available; otherwise, a new, larger buffer is allocated, data from the original buffer is copied to the new buffer, and the new data is then appended to the new buffer. The performance of a concatenation operation for a String or StringBuilder object depends on the frequency of memory allocations. A String concatenation operation always allocates memory, whereas a StringBuilder concatenation operation allocates memory only if the StringBuilder object buffer is too small to accommodate the new data. Use the String class if you are concatenating a fixed number of String objects. In that case, the compiler may even combine individual concatenation operations into a single operation. Use a StringBuilder object if you are concatenating an arbitrary number of strings; for example, if you're using a loop to concatenate a random number of strings of user input. References: http://msdn.microsoft.com/en-us/library/system.text.stringbuilder(v=vs.110).aspx