omniORB supports interceptors that allow the application to insert
processing in various points along the call chain, and in various
other locations. It does not (yet) support the standard Portable
Interceptors API.
The interceptor interfaces are defined in a single header,
include/omniORB4/omniInterceptors.h. Each interception point
consists of a singleton object with add() and remove() methods,
and the definition of an ‘interceptor info’ class. For example:
class omniInterceptors {
...
class clientSendRequest_T {
public:
class info_T {
public:
GIOP_C& giop_c;
IOP::ServiceContextList service_contexts;
info_T(GIOP_C& c) : giop_c(c), service_contexts(5) {}
private:
info_T();
info_T(const info_T&);
info_T& operator=(const info_T&);
};
typedef CORBA::Boolean (*interceptFunc)(info_T& info);
void add(interceptFunc);
void remove(interceptFunc);
};
...
};
You can see that the interceptors themselves are functions
that take the info_T object as their argument and return
boolean. Interceptors are called in the order they are registered;
normally, all interceptor functions return true, meaning that
processing should continue with subsequent interceptors. If an
interceptor returns false, later interceptors are not called. You
should only do that if you really know what you are doing.
Notice that the info_T contains references to omniORB internal
data types. The definitions of these types can be found in other
header files within include/omniORB4 and
include/omniORB4/internal.
10.1 Interceptor registration
All the interceptor singletons are registered within another singleton
object of class omniInterceptors. You retrieve a pointer to the
object with the omniORB::getInterceptors() function, which
must be called after the ORB has been initialised with
CORBA::ORB_init(), but before the ORB is used. The code to
register an interceptor looks, for example, like:
omniInterceptors* interceptors = omniORB::getInterceptors();
interceptors->clientSendRequest.add(myInterceptorFunc);
10.2 Available interceptors
The following interceptors are available:
- encodeIOR
Called when encoding an IOR to represent an object reference. This
interception point allows the application to insert extra profile
components into IORs. Note that you must understand and adhere to the
rules about data stored in IORs, otherwise the IORs created may be
invalid. omniORB itself uses this interceptor to insert various items,
so you can see an example of its use in the
insertSupportedComponents() function defined in
src/lib/omniORB/orbcore/ior.cc.- decodeIOR
Called when decoding an IOR. The application can use this to get out
whatever information they put into IORs with encodeIOR. Again, see
extractSupportedComponents() in
src/lib/omniORB/orbcore/ior.cc for an example.- clientOpenConnection
Called as a client opens a new connection to a server, after the
connection is opened but before it is used to send a request. The
interceptor function can set the info_T’s reject member
to true to cause the client to immediately close the new connection
and throw CORBA::TRANSIENT to the calling code. In that case, the
interceptor function can also set the why member to provide a
message that is logged.- clientSendRequest
Called just before a request header is sent over the network. The
application can use it to insert service contexts in the header. See
setCodeSetServiceContext() in
src/lib/omniORB/orbcore/cdrStream.cc for an example of its use.- clientReceiveReply
Called as the client receives a reply, just after unmarshalling the
reply header. Called for normal replies and exceptions.- serverAcceptConnection
Called when a server accepts a new incoming connection, but before
it reads any data from it. The interceptor function can set the
info_T’s reject member to true to cause the server to
immediately close the new connection. In that case, the interceptor
function can also set the why member to provide a message
that is logged.- serverReceiveRequest
Called when the server receives a request, just after unmarshalling
the request header. See the getCodeSetServiceContext() function in
src/lib/omniORB/orbcore/cdrStream.cc for an example.- serverSendReply
Called just before the server marshals a reply header.- serverSendException
Called just before the server marshals an exception reply header.- createIdentity
Called when the ORB is about to create an ‘identity’ object to
represent a CORBA object. It allows application code to provide its
own identity implementations. It is very unlikely that an application
will need to do this.- createORBServer
Used internally by the ORB to register different kinds of server. At
present, only a GIOP server is registered. It is very unlikely that
application code will need to do this.- createThread
Called whenever the ORB creates a thread. The info_T class for
this interceptor is class info_T {
public:
virtual void run() = 0;
};
The interceptor function is called in the context of the newly created
thread. The function must call the info_T’s run()
method, to pass control to the thread body. run() returns just
before the thread exits. This arrangement allows the interceptor to
initialise some per-thread state before the thread body runs, then
release it just before the thread exits.
- assignUpcallThread
The ORB maintains a general thread pool, from which threads are drawn
for various purposes. One purpose is for performing upcalls to
application code, in response to incoming CORBA calls. The
assignUpcallThread interceptor is called when a thread is assigned to
perform upcalls. In the thread per connection model, the thread stays
assigned to performing upcalls for the entire lifetime of the
underlying network connection; in the thread pool model, threads are
assigned for upcalls on a per call basis, so this interceptor is
triggered for every incoming call1. As with the
createThread interceptor, the interceptor function must call the
info_T’s run() method to pass control to the upcall.When a thread finishes its assignment of processing upcalls, it
returns to the pool (even in thread per connection mode), so the same
thread can be reassigned to perform more upcalls, or reused for a
different purpose.
Unlike the other interceptors, the interceptor functions for
createThread and assignUpcallThread have no return value. Interceptor
chaining is performed by calls through the info_T::run() method,
rather than by visiting interceptor functions in turn.