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CS 696 Emerging Technologies: Distributed Objects |
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Spring Semester, 1998
Naming Service
To Lecture Notes Index
© 1998, All Rights Reserved, SDSU & Roger Whitney
San Diego State University -- This page last updated 21-Apr-98
Contents of Doc 26, Naming Service
- References
- Design Principles
- IDL Definition of Naming Service
- NameComponent
- Name
- Naming Context
- Name Space
- Naming Service, OrbixWeb, IOR's
CORBAservices, chapter 3, Naming Service Specification, March 1995
OrbixWeb Programmer's Guide, IONA Technologies PLC, November 1997,
chapter 8 Making Objects Available in OrbixWeb pp. 180-202
Name Service does not give the names any semantic or interpretation
Names are structures of strings
Naming service clients need not be aware of the physical site of name servers
or which server contains which part of a compound name
No security is provided by the naming service
Naming contexts can be combined into arbitrary structures
module CosNaming
{
typedef string Istring;
// Istring is a name holder for possible future international
// string type
struct NameComponent {
Istring id;
Istring kind;
};
typedef sequence <NameComponent> Name;
enum BindingType {nobject, ncontext};
struct Binding {
Name binding_name;
BindingType binding_type;
};
typedef sequence <Binding> BindingList;
interface BindingIterator;
interface NamingContext {
enum NotFoundReason { missing_node, not_context,
not_object};
exception NotFound {
NotFoundReason why;
Name rest_of_name;
};
exception CannotProceed {
NamingContext cxt;
Name rest_of_name;
};
exception InvalidName{};
exception AlreadyBound {};
exception NotEmpty{};
void bind(in Name n, in Object obj) raises( NotFound,
CannotProceed, InvalidName, AlreadyBound);
void rebind(in Name n, in Object obj)
raises(NotFound, CannotProceed, InvalidName);
void bind_context(in Name n, in NamingContext nc)
raises(NotFound, CannotProceed, InvalidName,
AlreadyBound);
void rebind_context(in Name n, in NamingContext nc)
raises(NotFound, CannotProceed, InvalidName);
Object resolve (in Name n)
raises(NotFound, CannotProceed, InvalidName);
void unbind(in Name n)
raises(NotFound, CannotProceed, InvalidName);
NamingContext new_context();
NamingContext bind_new_context(in Name n)
raises(NotFound, AlreadyBound, CannotProceed,
InvalidName);
void destroy( ) raises(NotEmpty);
void list (in unsigned long how_many, out BindingList bl,
out BindingIterator bi);
};
interface BindingIterator {
boolean next_one(out Binding b);
boolean next_n(in unsigned long how_many, out BindingList bl);
void destroy();
};
};
struct NameComponent {
Istring id;
Istring kind;
};
A name in the naming service has two parts: id and kind
id
- The name part of the name
kind
- The type of thing
CORBA Naming Service does not provide any meaning to id or kind
That is your application can use them however you want
Sample Usage: file names
id = name of the file
kind = suffix of the file, .o, .java, .bin, .c, etc.
typedef sequence <NameComponent> Name;
A name is sequence of Naming components
This allows hierarchical names
Example
The file:
/ma/home/whitney/CosNaming.idl
could
be represented by:
NamingComponent[] name_module =
new NamingComponent[4];
name_module[0] = new NamingComponent("ma", "dir");
name_module[1] = new NamingComponent("home", "dir");
name_module[2] = new NamingComponent("whitney", "dir");
name_module[3] = new NamingComponent("CosNaming", "idl");
A NamingContext can contain other NamingContexts and objects
Each item in a NamingContext has an associated name
The name is bound to the item via Binding struct
Analogies
File structure
- NamingContext is like a directory
-
- Objects are like files
Tree
-
- NamingContext is like an internal node of tree in that it can point
(contain) to other internal nodes and leaves
-
- Object is like a leaf
-
- Note NamingContext structure is not limited to being a tree it can be an
arbitrary graph
All valid names recognized by the Naming Service is called a name space
A name space can span multiple machines and servers
A client can:
- connect to the NamingService,
-
- give it a name,
-
- receive the object associated with that name
-
- and not know which machine or server actually holds the object
Naming context's are combined together to form a naming network in the naming
space
enum BindingType {nobject, ncontext};
struct Binding {
Name binding_name;
BindingType binding_type;
};
A name can be bound to:
- a Naming context (ncontext) to be part of the structure of the Name Space
-
- an object (nobject) to be something we want to access in the Name
Space
Operations to Create Contexts andName Space Structure
void bind_context(in Name n, in NamingContext nc)
raises(NotFound, CannotProceed, InvalidName, AlreadyBound);
Make parameter nc a subcontext of the receiver,
The parameter nc is bound to the name n
All but the final naming component of parameter n must be bound to
naming contexts which are part of the Name Space structure
An exception is thrown if the last name component is already bound
The last name component is the context name
void rebind_context(in Name n, in NamingContext nc)
raises(NotFound, CannotProceed, InvalidName);
Same as bind_context, but nc is an existing and bound naming context
NamingContext new_context();
Return
a new context which is not bound to a name or part of a naming context, hence
is not in the name space structure
NamingContext bind_new_context(in Name n)
raises(NotFound, AlreadyBound, CannotProceed, InvalidName);
Create a new naming context that is a bound subcontext of the receiver
The new context is also bound to the given name
Binding Names to Objects
void bind(in Name n, in Object obj)
raises( NotFound, CannotProceed, InvalidName, AlreadyBound);
Binds the object to the given name
If the name n only has one component, that is the name the object is
bound to, and the name-object binding is added to the receiving naming
context
If the name n has more than one component, all but the last component
are used to find the naming context to which to add the name-object binding
void rebind(in Name n, in Object obj)
raises(NotFound, CannotProceed, InvalidName);
Same as bind, but rebinds the name to a different object
Resolving Names
Object resolve (in Name n)
raises(NotFound, CannotProceed, InvalidName);
Returns the object bound to the given name, relative to the target naming
context
Note: returns a type org.omg.CORBA.Object
Use <type>Helper.narrow( ) to cast the object to its actual type
Do not use the normal Java cast operator to cast the object to its actual
type
Deleting
void unbind(in Name n)
raises(NotFound, CannotProceed, InvalidName);
Removes the binding between the specified name and the object it is resolved
to
void destroy( ) raises(NotEmpty);
Deletes the naming context on which it is invoked
The naming context can not contain any bindings
Listing names
struct Binding {
Name binding_name;
BindingType binding_type;
};
typedef sequence <Binding> BindingList;
interface BindingIterator {
boolean next_one(out Binding b);
boolean next_n(in unsigned long how_many, out BindingList bl);
void destroy(); //destorys the BindingIterator
};
void list (in unsigned long how_many,
out BindingList bl,
out BindingIterator bi);
how_many
specifies the maximum number of bindings that should be returned in the
BindingList parameter
If there are more than this, than the remainder are returned in the
BindingIterator
If the naming context does not contain any additional bindings, the parameter
bi will be a nil object reference
Note: bl and bi are out parameters, so in Java they will be
passed in holder objects
next_one and next_n return true if they returned any bindings,
other wise they return false
The naming service stores bound objects as IOR, a string version of the
object
The IOR is different for the different protocols: IIOP and Orbix native
In IIOP the port number of the server is part of the IOR for an object
If the server changes ports the IOR is no longer valid
So either make sure that the server always uses the same port or never goes
down
I have not been successful in getting a server to use the same port on
restart
visitors since 31-Mar-98