Method Caller PID and disconnection from session dbus

[yousefvand]

Considering server example and process A and B if one of them calls Foo method, how can I find it's PID and say it was A for example.
If both A and B are connected to session dbus and B gets disconnected from session dbus how can I inform about that (this is possible in C++ dbus library).

[guelfey]

Considering server example and process A and B if one of them calls Foo method, how can I find it's PID and say it was A for example.

This is right now not possible with the "high-level" server mechanisms, but you can use Eavesdrop to get the sender of messages as well, and then query the process id of the sender using org.freedesktop.DBus.GetConnectionUnixProcessID.

If both A and B are connected to session dbus and B gets disconnected from session dbus how can I inform about that (this is possible in C++ dbus library).

Not sure if I understand you correctly; my best guess would be https://dbus.freedesktop.org/doc/dbus-specification.html#bus-messages-name-lost. If you have the C++ library ready, do you have a link to the documentation of this and/or some example code for what you mean?