About Us Products Articles News Contact Support

Programming Distributed Systems with YAMI4

8.1.1 Connection Event Notifications

One of the important features of the YAMI4 agent is the ability to report connection-related events to the user. The reported events are:

• new outgoing connection is open - this is reported whenever a new channel is created as a result of user action
• new incoming connection is open - when a listener accepts the connection from some remote agent
• connection is closed - when the channel is closed either explicitly or implicitly as a result of communication error or regular end-of-stream condition

In order to enable connection event reporting, the user has to provide the callback either at the time the agent is created to the appropriately overloaded agent constructor or by calling a dedicated registering function on the agent. This is done differently in each supported programming language:

• In Ada the user has to provide callback object that implements the Handler interface defined in the YAMI.Connection_Event_Handlers package. The callback is registered with a separate operation of the Agent type.
• In C++ the callback, which can be any callable entity that can accept a function-like call with two arguments - the connection name of std::string type and the enumeration representing event kind - has to be registered with a separate function of the agent class.
• In Java the user callback has to implement the ConnectionEventCallback interface and is provided when the agent is constructed.
• In .NET the user callback for connection events notifications can be added to the agent by means of a delegate via the publicly available ConnectionsChanged event.
• In Python the user callback can be any callable entity that accepts server name and event kind and is provided to the Agent's constructor.

If the callback is installed, the notification is performed within the context of the thread that initiated the event - this might be the user thread for opening outgoing connection, or the internally managed worker thread for opening incoming connections or closing them due to end of stream condition. The user-provided implementation of the callback should therefore not block or delay the execution unnecessarily.