In this chapter, we introduce the omniORB2 API. The purpose
of this API is to provide access points to omniORB2 specific
functionalities that are not covered by the CORBA specification.
Obviously, if you use this API in your application, that part of your code
is not going to be portable to run unchanged on other vendors' ORBs. To
make it easier to identify omniORB2 dependent code, this API is defined
under the name space ``omniORB''
.
CORBA::ORB_init accepts the following command-line arguments:
BOA_init accepts the following command-line arguments:
By default, the BOA can work out the IP address of the host machine. This address is recorded in the object references of the local objects. However, when the host has multiple network interfaces and multiple IP addresses, it may be desirable for the application to control what address the BOA should use. This can be done by defining the environment variable OMNIORB_USEHOSTNAME to contain the preferred host name or IP address in dot-numeric form. Alternatively, the same can be acheived using the -BOAiiop_name_port option.
As defined in the CORBA specification, any command-line arguments understood by the ORB/BOA will be removed from argv when the initialisation functions return. Therefore, an application is not required to handle any command-line arguments it does not understand.
OmniORB2 uses the C++ iostream cerr to output any tracing and diagnostic messages. Some or all of these messages can be turned-on/off by setting the variable omniORB::traceLevel. The type definition of the variable is:
CORBA::ULong omniORB::traceLevel = 1; // The default value is 1
At the moment, the following trace levels are defined:
The variable can be changed by assignment inside your applications. It can also be changed by specifying the command-line option: -ORBtraceLevel <level>. For instance:
$ eg2_impl -ORBtraceLevel 5
Applications can optionally specified a name to identify the server process. At the moment, this name is only used by the host-based access control module. See section 7.5 for details.
The name is stored in the variable omniORB::serverName.
CORBA::String_var omniORB::serverName;
The variable can be changed by assignment inside your applications. It can also be changed by specifying the command-line option: -ORBserverName <string>.
OmniORB2 uses a data type omniORB::objectKey to uniquely identify each object implementation. This is an opaque data type and can only be manipulated by the following functions:
void omniORB::generateNewKey(omniORB::objectKey &k);
omniORB::generateNewKey returns a new objectKey. The return value is guaranteed to be unique among the keys generated during this program run. On the platforms that have a realtime clock and unique process identifiers, a stronger assertion can be made, i.e. the keys are guaranteed to be unique among all keys ever generated on the same machine.
const unsigned int omniORB::hash_table_size; int omniORB::hash(omniORB::objectKey& k);
omniORB::hash returns the hash value of an objectKey. The value returned by this function is always between 0 and omniORB:hash_table_size - 1 inclusively.
omniORB::objectKey omniORB::nullkey();
omniORB::nullkey always returns the same objectKey value. This key is guaranteed to hash to 0.
int operator==(const omniORB::objectKey &k1,const omniORB::objectKey &k2); int operator!=(const omniORB::objectKey &k1,const omniORB::objectKey &k2);
ObjectKeys can be tested for equality using the overloaded operator== and operator!=.
omniORB::seqOctets* omniORB::keyToOctetSequence(const omniORB::objectKey &k1); omniORB::objectKey omniORB::octetSequenceToKey(const omniORB::seqOctets& seq);
omniORB::keyToOctetSequence takes an objectKey and returns its externalised representation in the form of a sequence of octets. The same sequence can be converted back to an objectKey using omniORB::octetSequenceToKey. If the supplied sequence is not an objectKey, omniORB::octetSequenceToKey raises a CORBA::MARSHAL exception.
omniORB2 sets a limit on the GIOP message size that can be sent or received. The value can be obtained by calling:
size_t omniORB::MaxMessageSize();and can be changed by:
void omniORB::MaxMessageSize(size_t newvalue);
or by the command-line option -ORBgiopMaxMsgSize.
The exact value is somewhat arbitrary. The reason such a limit exists is to provide some way to protect the server side from resource exhaustion. Think about the case when the server receives a rogue GIOP(IIOP) request message that contains a sequence length field set to 2**31. With a reasonable message size limit, the server can reject this rogue message straight away.
Starting from 2.6.0, a new mechanism is available for the ORB runtime to
obtain the initial object references to CORBA services. Previously, it is
necessary to write the IOR string of these services in the configuration
file (section 1.2). Now the object references can be obtained from
a bootstrap service. The bootstrap service is a special object with the
object key 'INIT' and the following interface.:
// IDL
module CORBA {
interface InitialReferences {
Object get(in ORB::ObjectId id);
// returns the initial object reference of the service
// identified by <id>. For example the id for the COSS
// Naming service is "NameService".
ORB::ObjectIdList list();
// returns the list of service id that this agent knows of
// their initial object reference.
};
};
By default, all omniORB2 servers, i.e. those applications with the BOA initialised, contains an instance of this object and is able to responds to remote invocations. To prevent the ORB from instantiating this object, the command-line option -BOAno_bootstrap_agent should be specified.
In particular, the Naming Service omniNames is able to respond to a query through this interface and returns the object reference of its root context. In effect, the bootstrap agent provides a level of indirection. All omniORB2 clients still have to be supplied with the address of the bootstrap agent. However the information is much easier to specify than a stringified IOR! Another advantage of this approach is that it is completely compatiable with JavaIDL. This makes it possible for a client written in JavaIDL to share with a omniORB2 server the same Naming Service.
The address of the bootstrap agent is given by the ORBInitialHost and ORBInitialPort parameter in the omniORB configuration file (section 1.2). The parameters can also be specified as command-line options (section 4.1). ORBInitialHost is the host name and ORBInitialPort is the TCP/IP port number. The parameter ORBInitialPort is optional. If it is not specified, port number 900 will be used.
During initialisation, the ORB reads the parameters in the omniORB configuration file. If the parameter NAMESERVICE is specified, the stringified IOR would be used as the object reference of the root naming context. If the parameter is absent and the parameter ORBInitialHost is present, the ORB would contact the bootstrap agent at the address specified to obtain the root naming context when the application calls resolve_initial_reference(). If neither the NAMESERVICE nor ORBInitialHost is present, a call to resolve_initial_reference() returns a nil object. Finally, the command line argument -ORBInitialHost overrides any parameters in the configuration file. The ORB would always contact the bootstrap agent at the address specified to obtain the root naming context.
Now we are ready to describe a simple way to set up omniNames.
$ omniNames -start 1234
ORBInitialHost wobble
ORBInitialPort 1234
Alternatively, the command line options can be used, for example:
$ eg3_impl -ORBInitialHost wobble -ORBInitialPort 1234 &
$ eg3_clt -ORBInitialHost wobble -ORBInitialPort 1234
Sometimes, to cope with bugs in another ORB, it is necessary to disable various GIOP and IIOP features in order to achieve interoperability. If the command line option -ORBlcdMode or the function omniORB::enableLcdMode() is called, the ORB enters the so-called ``lowest common denominator mode''. It bends over backwards to cope with bugs in the ORB at the other end. This is purely a transitional measure. The long term solution is to report the bugs to the other vendors and ask them to fix them expediently.
By default, omniORB2 uses GIOP LOCATE_REQUEST message to verify the existence of an object prior to the first invocation. If another vendor's ORB is known not to be able to handle this GIOP message, set the variable omniORB::verifyObjectExistsAndType to 0 would disable this feature, and hence achieve interoperability. The option can also be set via the command line option -ORBverifyObjectExistsAndType.
class fatalException {
public:
const char *file() const;
int line() const;
const char *errmsg() const;
};
When omniORB2 detects an internal inconsistency that is most likely to be caused by a bug in the runtime, it raises the exception omniORB::fatalException. When this exception is raised, it is not sensible to proceed with any operation that involves the ORB's runtime. It is best to exit the program immediately. The exception structure carries by omniORB::fatalException contains the exact location (the file name and the line number) where the exception is raised. You are strongly encourage to file a bug report and point out the location.
It may help to cause a core-dump and look at the stack trace to locate where the exception was thrown. This can be done by setting the variable omniORB::abortOnInternalError to 1. The variable can also be set via the command line option -ORBabortOnInternalError.