Shared Memory Applications in C#

As explained in the Shared Memory Applications page, allows two or more processes to share a common database. General instructions are given there explaining how shared memory segments must be created on different operating systems. Further implementation details for C# applications are provided in the following sections.

Example

The following code snippet demonstrates how a process initializes a shared memory device, then uses a try-catch blocks to and open or connect to a database in shared-memory:

    public class Open

    {

        const int PAGE_SIZE = 128;

        const int DATABASE_SIZE = 1610241024;

        // create Database object and define global connection instance

        public static Database db = new Database(new SmartEDBWrapper());

        public static Connection con;

       

        public static void OpenSharedDb(

            String dbName,        // name of the database

            Int32  dbSize,        // size of memory segment for in-mem part

            Int32  pgSize,        // size of memory page

            Int32  maxConnections // max. number of connections

        )

        {

            Database.Device[] devs = new Database.Device[1];

            Database.Parameters parameters = new Database.Parameters();

            parameters.MemPageSize = pgSize;

            parameters.Classes = new Type[] { typeof(Obj) }; // list of database          classes

            parameters.MaxConnections = maxConnections;

            devs[0] = new Database.SharedMemoryDevice(

                        Database.Device.Kind.Data,

                        dbName + “-db”,

                        new IntPtr(0), dbSize);

            try

            { // Open database. If already opened an exception is thrown

                db.Open("opendb", parameters, devs);       

            }

            catch (DatabaseError dbe)

            {

                // Note that code 66 = “duplicate instance” is a valid case

                // for a Shared-memory database; the secondary application

                // will connect to the existing database. So this exception is

                // ignored and the application continues. Other exceptions are

                // handled below…

                if (dbe.errorCode != 66)

                {

                    if (dbe.errorCode == 62)

                        Console.WriteLine("SmartEDB assembly is not

                            compatible with option 'shm'. Please replace 

                            reference to THE assembly with 

                            shared memory                                       functionality");

                    else if (dbe.errorCode == 620000)

                        Console.WriteLine("SmartEDB assembly is not

                            compatible with option 'disk'. Please replace

                            reference to assembly with disk manager

                            functionality");

                    throw dbe;

                    // equivalent to return MCO_E_UNSUPPORTED;

                }

            }

        }

        public static void ConnectDb()

        {

            try

            {

                con = new Connection(db); // connect to the database

            }

            catch (DatabaseError dbe)

            {

                throw dbe;

            }

        }

   

        public static void Main(String[] args)

        {

            try

            {

                // This method starts the database runtime and opens a

                // new database or detects if the shared memory database is

                // already opened.

                OpenSharedDb("sharedDb", DATABASE_SIZE, PAGE_SIZE, 1);

               

                // Connect to the new or existing shared-memory database

                ConnectDb();

                // Normal database processing goes here

                con.Disconnect();

                db.Close();

            }

            catch (DatabaseError dbe)

            {

                Console.WriteLine("\n\nError %d creating/connecting shared

                            memory database.\n", dbe.errorCode);

            }

            Console.ReadLine();

        }

    }

   

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