readme

支持组件模型CCM的开源中间件-mico

There are some cases where _narrow() needs to make remote invocations. 
Because this is expensive you can tell the IDL whether or not to
generate code that makes remote invocations using
--do-not-query-server-for-narrow. The following discussion explains
when you can use --do-not-query-server-for-narrow.


Consider the following scenario: you have a server which maintains
references to an interface called "base". This server is defined by
the files base.idl, base_impl.[h|cc] and server.cc. Once the server is
compiled and linked, it is started.

At a later point in time someone decides to define a new interface
"derived" which inherits from "base". The client makes use of both
base and derived and therefore needs all the files in this directory.

What happens if the server, which is still running, is getting a
reference to "derived"? It should pose no problems according to the
CORBA subtyping rules. But how does the server know that "derived"
IS-A "base"?

One way would be to stop the server, re-link it with the
implementation of derived and then get it up and running again.
Sometimes it is not desirable to stop the server. In that case the
only way for the server to know about "derived" IS-A "base" is to
ask the client that generated the "derived" object.

Since this means a significant time overhead (each failed _narrow()
will do a query to the server), you can omit this behaviour by using
the --do-not-query-server-for-narrow command line option. The code
generated for _narrow() only queries the server if you do not use the
--do-not-query-server-for-narrow switch. Beware that incorrect use
will result in failing _narrow() although it shouldn't.

BTW: the content of this README should be moved to the docs...