WHAT-IS: context

Table Of Contents

• Definition
• What is a "context" ?

Definition

context

the real application using the libmsgque interface and service handles

What is a "context" ?

• the context is the main libmsgque object with a different purpose on a client and a server and is created with:

  MqErrorCheck (MqLinkCreate ((struct ContextS *)context, argv, alfa, &context->msgque));
  

  • the client context is an object of the type MqS and it is the return value of the call to MqLinkCreate .
  • the server context is defined with the MqSetupS::isServer configuration option to MqLinkCreate and a server specific wrapper around the MqS struct. The server context is created in a server specific startup code with the following purpose:
    • create the server specific context.
    • create the libmsgque specific context MqS with MqLinkCreate.
    • adding the services or the filter.
    • doing a server context specific setup.
• both client and server are able to create multiple context.
• every client is able to create multiple server-parent context.
• every server is able to create multiple client-parent context.

  --App-1---|-----------App-21-----------|---App-31--
            |                            |
            |             *- client211 ->|-> server31
            |             *              |
            |-> server21 -*              |---App-32--
            |             *              |
            |             *- client212 ->|-> server32
            |                            |
  client1 ->| ----------App-22-----------|---App-33--
            |                            |
            |             *- client221 ->|-> server33
            |             *              |
            |-> server22 -*              |---App-34--
            |             *              |
            |             *- client222 ->|-> server34
  

  • The setup from above is connecting 7 individual applications (App-1 - App-34) together.
  • Every individual application is consuming one process or thread.
  • client1 from App-1 is starting/connecting to server21 from App-21 and server22 from App-22
  • server21 is creating the client211 and client212 in App-21
  • client211 from App-21 is starting/connecting to server31 from App-31
  • ...
• every context on the client has a link to a context on the server.
• every context is able to provide different service handles.
• every handle is recognized by a 4 character token and have to be unique per context.
• a handle can be dynamically added or removed.
  using libmsgque code (example)

    return MqServiceCreate(ctx,"MMUL", MMUL, NULL, NULL);
  

  using ccmsgque code (example)

        ServiceCreate("MMUL", CallbackF(&mulserver::MMUL));
  

  using csmsgque code (example)

        ServiceCreate("MMUL", MMUL);
  

  using javamsgque code (example)

      ServiceCreate("MMUL", new MMUL());
  

  using tclmsgque code (example)

    $ctx ServiceCreate "MMUL" MMUL
  

  using pymsgque code (example)

    ctx.ServiceCreate("MMUL",MMUL)
  

  using perlmsgque code (example)

      $ctx->ServiceCreate("MMUL",\&MMUL)
  

  using vbmsgque code (example)

        ServiceCreate("MMUL", AddressOf MMUL)
  

• the service handle is needed to supply a 'service' usable by a remote context
  using libmsgque code (example)

  static enum MqErrorE  MMUL( struct MqS *ctx, MQ_PTR data) {
    MQ_DBL d1,d2;
    MqErrorCheck (MqSendSTART(ctx));
    MqErrorCheck (MqReadD(ctx, &d1));
    MqErrorCheck (MqReadD(ctx, &d2));
    MqErrorCheck (MqSendD(ctx, d1*d2));
  error:
    return MqSendRETURN(ctx);
  }
  

  using ccmsgque code (example)

      void MMUL () {
        SendSTART();
        SendD(ReadD() * ReadD());
        SendRETURN();
      }
  

  using csmsgque code (example)

      public void MMUL () {
        SendSTART();
        SendD(ReadD() * ReadD());
        SendRETURN();
      }
  

  using javamsgque code (example)

    class MMUL implements IService {
      public void Service (MqS ctx) throws MqSException {
        SendSTART();
        SendD(ReadD() * ReadD());
        SendRETURN();
      }
    }
  

  using pymsgque code (example)

  def MMUL(ctx):
    ctx.SendSTART()
    ctx.SendD(ctx.ReadD() * ctx.ReadD())
    ctx.SendRETURN()
  

  using tclmsgque code (example)

    sub MMUL {
      my $ctx = shift;
      $ctx->SendSTART();
      $ctx->SendD($ctx->ReadD() * $ctx->ReadD());
      $ctx->SendRETURN();
    }
  

  using vbmsgque code (example)

      Private Sub MMUL()
        SendSTART()
        SendD(ReadD() * ReadD())
        SendRETURN()
      End Sub