Commands | AMQP1 Sessions

In the context of the AMQP (Advanced Message Queuing Protocol) 1.0.0 specification, a session represents a logical context for communication between a client and a message broker. Here's a breakdown of what an AMQP 1.0.0 session entails:

 

• Logical Context: A session establishes a logical context for messaging operations between an AMQP client (producer or consumer) and an AMQP broker. It provides a way to group related messaging operations together within a single connection.
• Communication Channel: Sessions serve as communication channels over which messages are sent and received. They encapsulate the exchange of messages, acknowledgments, and flow control mechanisms.
• Transactional Boundaries: Sessions define transactional boundaries for message operations. They enable the grouping of multiple message sends or receives into a single atomic unit, ensuring that either all operations within the session are processed successfully or none are processed at all.
• Flow Control: Sessions support flow control mechanisms to regulate the rate at which messages are exchanged between the client and the broker. Flow control helps prevent overwhelming the resources of either party, ensuring efficient and reliable message delivery.
• Lifetime Management: Sessions have a lifecycle that begins when they are created and ends when they are closed. Clients can establish multiple sessions within a single connection to parallelize message processing or isolate message streams.
• Resource Allocation: Sessions may be associated with specific resources such as queues, topics, or subscriptions within the broker. Messages sent or received within a session are bound to these resources, enabling targeted message routing and delivery.

 

In summary, an AMQP 1.0.0 session provides a logical context for message exchange between an AMQP client and broker, facilitating transactional integrity, flow control, and resource management within the messaging system. It defines the boundaries within which messaging operations are performed and helps ensure the efficient and reliable exchange of messages.

 

 

Open Session

The method CreateSession creates a new session with the given name (or if empty, it creates with a random name), if the session already exists an exception is raised. The client allows you to create multiple session using the same AMQP connection.

 

Once the session is successfully created, the event OnAQMPSessionOpen is fired.

 

oAMQP.CreateSession('MySession');
procedure OnAMQPSessionOpen(Sender: TObject; const aSession: TsgcAMQP1Session; const aBegin: TsgcAMQP1FrameBegin);
begin
  ShowMessage('#session-open: ' + aSession.Id);
end;

 

The CreateSession method returns the TsgcAMQP1Session class which contains the session information.

 

 

Await Open Session

 

By default, the CreateSession method is Asynchronous, so after calling the method, the code continue. If you want to wait till the CreateSession method is completed and the confirmation sent by the server is received, set the property Await to True in the Options parameter.

 

procedure OpenSession(const aSession: string);
var
  oOptions: TsgcAMQP1MethodOptions_SessionOpen;
begin
  oOptions := TsgcAMQP1MethodOptions_SessionOpen.Create;
  Try
    oOptions.Await := True;
    AMQP1.CreateSession(aSession, oOptions);
  Finally
    oOptions.Free;
  End;
end;

 

Close Session

To Close an existing session use the method CloseSession passing the name of the session to close.

 

Once the session is successfully closed, the event OnAQMPSessionClose is fired.

oAMQP.CloseSession('MySession');
procedure OnAMQPSessionCloseEvent(Sender: TObject; const aSession: TsgcAMQP1Session; const aEnd: TsgcAMQP1FrameEnd);
begin
  ShowMessage('#session-close: ' + aSession.Id + ' [' + IntToStr(aSession.Channel) + ']' + ' reason: ' + aEnd.Error.Condition);
end;

 

Await Close Session

 

By default, the CloseSession method is Asynchronous, so after calling the method, the code continue. If you want to wait till the CloseSession method is completed and the confirmation sent by the server is received, set the property Await to True in the Options parameter.

 

procedure CloseSession(const aSession: string);
var
  oOptions: TsgcAMQP1MethodOptions_SessionClose;
begin
  oOptions := TsgcAMQP1MethodOptions_SessionClose.Create;
  Try
    oOptions.Await := True;
    AMQP1.CloseSession(aSession, oOptions);
  Finally
    oOptions.Free;
  End;
end;