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This directory contains files that implement a server for the TAO
Naming Service. In addition, it contains files that run the TAO
Naming Service as a Windows NT Service. Both of these services are
described below.
How to Run the TAO Naming Service
=================================
The following describes how to run the TAO Naming Service.
1. Syntax
% tao_cosnaming [-ORBNameServicePort nsport]
[-b base_address]
[-d ]
[-f persistence_file_name]
[-m (1=enable multicast responses,0=disable(default)]
[-n number_of_threads]
[-o ior_output_file]
[-p pid_file_name]
[-r directory]
[-s context_size]
[-t time]
[-u directory]
[-z time]
2. Optional Command-line Arguments
-ORBNameServicePort nsport
Multicast port for listening for requests from clients
trying to bootstrap to a Naming Service through the
use of multicast. This is only used when multicast
responding is enabled via '-m 1'.
-b base_address
The address used for memory mapping the file specified
with the "-f" option above. The value supplied with
this option is only used when the Naming Service runs
in persistent mode, i.e., "-f" option is present.
-d
Provides Naming Service specific debug information. By default
no diagnostics are given.
-f persistence_file_name
The name of the file to use to store/retrieve
persistent state of the Naming Service. Without this
option, Naming Service is started in non-persistent
mode.
-m <0|1>
TAO offers a simple, very non-standard method for
clients to discover the initial reference for the
Naming Service. However, since it can be inadequate and cause
unexpected results if, for example, there are multiple
naming services running on the network, the DEFAULT
behavior is for the Naming Service to NOT RESPOND to
such multicast queries (use the Interoperable Naming
Service bootstrap options instead).
-n number_of_threads
Specify a number of threads to be used to run the ORB.
Default is 1.
-o ior_output_file
The name of the file, in which to store the IOR of the
root Naming Service context.
-p pid_file_name
The name of the file, in which to store the process id
of the Naming Service server.
-s context_size
Size of the hash table allocated for the root Naming
Context (if one is created). All contexts created
under the root will use the same size for their hash
tables. The default is 1024.
-t time
How long (in seconds) the server should listen for
client requests before terminating.
-r directory
Use redundant flat-file persistence; same as the -u option,
except more than one instance of the TAO Naming Service server
can run, each using the same set of disk files, to achieve a
degree of fault tolerence (as long as directory is accessible
to both servers).
-u directory
Use a flat-file persistence implementation that stores object
reference information in a file per context. Each context file
is placed in the directory specified.
-z time
A relative round trip timeout value (in seconds) that
the service should wait for when trying to progress an
operation through a federated naming context before
timing out and throwing a 'Cannot proceed' exception
to the client. If no value is set this will never occur.
3. Environment Variables
NameServicePort
Multicast port for listening for requests from clients
trying to bootstrap to a Naming Service through the
use of multicast. This is only used when multicast
responding is enabled via '-m 1'.
4. Persistence
TAO Naming Service has an optional persistence capability. By
default, the Naming Service is started in a non-persistent
mode. Supplying "-f" command-line option to the server causes
a persistent version of the Naming Service to run.
The file specified with the "-f" option is used to store the
persistent state of the Naming Service, i.e., all Naming
Contexts and their bindings. When "-f" option is specified:
1. If the specified file does not exist, it is created and
used to store the state of the Naming Service. An initial
(root) Naming Context is also created.
2. If the specified file exists, it is scanned and:
a) If any inconsistency is detected in the stored
state, or the file is not recognized by the Naming
Service, the server exits. (This may happen, for
example, if a server or host crashed in the middle of
writing a record to this file on a previous run). A
noncorrupted version of the file must be used instead.
b) If the file is recognized and is ok, the state
stored in the file becomes the current state of the
Naming Service.
Internally, TAO uses memory mapped file to implement
persistence feature of the Naming Service. A default memory
address (ACE_DEFAULT_BASE_ADDR) is used for mapping the file.
Alternate mapping address can be specified at compile-time by
redefining TAO_NAMING_BASE_ADDR in tao/orbconf.h. Alternate
mapping address can also be specified at run-time
with the "-b" command-line option, which takes precedence over
TAO_NAMING_BASE_ADDR definition.
NOTE: Naming Service stores absolute pointers in its
memory-mapped file. Therefore, it is important to use the
same mapping address on each run for the same persistence file.
5. Implementation Policies
a. Destroying Binding Iterators
A binding iterator is destroyed when client invokes
<destroy> operation either on the iterator itself or
on the naming context it is iterating over. In both
cases, subsequent calls on the binding iterator object
will cause OBJECT_NOT_EXIST exception.
b. Dealing with orphaned contexts
This implementation of the Naming Service does not
include any form of 'garbage collection' for orphaned
naming contexts. It is solely the responsibility of
clients to clean up after themselves and not leak
server resources. All the resources, including
orphaned contexts, are released during the Naming
Server shutdown.
6. Clients: ways to bootstrap to the Naming Service:
There are several methods for a client to bootstrap to a
Naming Service, i.e., there are several mechanisms
<resolve_initial_references> can use when asked for
"NameService". In order of predictable behavior, they are:
1. Command-line options
The "-ORBInitRef NameService=IOR:..." or environment
variable NameServiceIOR can be used on the client side
to specify the object that the call to
<resolve_initial_references> should return to the
client. (On the server side, -o option can be used to
get the ior).
Example (Unix, same host):
% $TAO_ROOT/orbsvcs/Naming_Service/tao_cosnaming -o ior_file
% my_client -ORBInitRef NameService=file://ior_file
On the first line, we start the Naming
Service, and output its ior to <ior_file>. On
the second line, we start some client, and
specify the ior <resolve_initial_references>
should return for the Naming Service in a file
format.
2. Interoperable Naming Service.
TAO implements the standard CORBA Interoperable Naming
Service (ING). Therefore, most initialization options
provided by INS can be used to bootstrap to the Naming
Service (see TAO's release notes for the status of INS
implementation).
3. Multicast
When started with the "respond to multicast queries"
option turned on ('-m 1'), clients can use IP
multicast to query for a Naming Service, and this
instance will respond. TAO Naming Server is listening
for client multicast requests on a specified port. On
the client side, <resolve_initial_references> sends
out a multicast request on the network, trying to
locate a Naming Service. When a Naming Server
receives a multicast request from a client, it replies
to the sender with the ior of its root Naming Context.
Note, the port used for this bootstrapping process,
i.e., 'multicast port', has nothing to do with the ORB
port used for CORBA communication. Other points worth
mentioning:
- A client and a server will only click through this
multicast protocol if they are using the same
multicast port. For both client and server
-ORBnameserviceport command-line option and
NameServicePort environment variable can be used to
specify the multicast port to use. If none is
specified, the default port is used. (The ability
to specify multicast ports can be used to match
certain clients with certain Naming Servers, when
there are more than one Naming Server running on the
network).
- If there are several Naming Servers running on the
network, each listening on the same port for
multicast requests, each will send a reply to a
client's request. The client's orb will use the
first response it receives, so the Naming Service
will, in fact, be selected at random.
Since this mechanism is proprietary to TAO (i.e.,
non-standard), it only works when both client and
server are written using TAO. There is no way to turn
multicasting off on the client side, but it is used
only as a last resort, i.e., any of the other options
will override it.
When OS platform doesn't support multicast, or client
or server isn't written using TAO, or a more
reliable/predictable location method is desired, etc.,
one of the other options can be used to bootstrap to
the Naming Service.
How to use the NT_Naming_Service
================================
A command line interface is provided to install, configure, start,
and stop the Naming service as a Windows service.
1. Syntax
% tao_nt_cosnaming [-i [n]]
[-c [args]]
[-r]
[-s]
[-k]
[-t n]
[-d]
2. Optional Command-line Arguments
-i [n]
Install this program as an NT service, with specified startup mode
-c [args]
Query or supply command line arguments for NT service.
-r
Remove this program from the Service Manager
-s
Start the service
-k
Kill the service
-t n
Set startup mode for an existing service
-d
Debug; run as a regular application
3. Usage
To see different stages of an NT service application, you have
to run the program several times, with different options.
Please note: run with only one option at a time. Only the
Administrator can run commands that modify state such as the -i
or -c options.
a. First, you must initialize the service in the NT SCM
database. Run tao_nt_cosnaming with -i [n], where n is a
number from 1 to 4, corresponding to these startup options:
// Start Type (from WinNT.h)
//
#define SERVICE_SYSTEM_START 0x00000001
#define SERVICE_AUTO_START 0x00000002
#define SERVICE_DEMAND_START 0x00000003
#define SERVICE_DISABLED 0x00000004
If only -i is specified, SERVICE_DEMAND_START is default option.
This option may only be run as Administrator.
b. For System or Auto start modes, or even Demand start and using the
-s option to start, any command line options, such as endpoint
specification or IOR publication, must be stored in the Windows
registry. Use tao_nt_cosnaming -c with no additional arguments to
see the current command line setting. Use tao_nt_cosnaming -c "args"
to provide a new command line for the registered name service. Be
sure to quote the args string. For example:
tao_nt_cosnaming -c "-ORBListenEndpoints iiop://%computername%:2809"
will yield:
tao_nt_cosnaming -c
-ORBListenEndpoints iiop://VIRTWIND:2809
Notice the environment variable used in the argument string was
expanded.
c. Now you are ready to run the actual service. Run
tao_nt_cosnaming -s.
d. To stop service execution, run tao_nt_cosnaming -k.
c. To remove the service from the Service Control Manager
database, run tao_nt_cosnaming -r.
In addition, once you have initialized this service (by using
the -i option) you can change its startup type to one of the
other values above. To do this, run tao_nt_cosnaming -t n, where
n is a number corresponding to one of the startup modes listed above.
In order to debug the service's execution itself, use the -d
option.
Troubleshooting
============================================
Q1. Error Message: "subscribe: no such device"
A1. On starting, the error message "subscribe: no such device" is a
rather cryptic message saying that basically either you don't support
multicasting or there is no route for multicasting on one of your
network interfaces( e.g. eth0 ).
---------------------------------------
(Step 1)
Check to see if you have multicasting enabled. In the case of Linux
you will need to check the configuration of your kernel. RedHat users
have multicasting enabled by default. Once you are sure that you have
multicast enabled then move to the next step. Alternative is to start
tao_cosnaming with multicast disabled.
---------------------------------------
(Step 2)
Check to see if you have the route for multicasting. Linux users can
do this by running:
/sbin/route
You should see something like this:
Kernel IP routing table
Destination Gateway Genmask Flags Metric Ref Use Iface
10.0.0.0 * 255.255.255.0 U 0 0 0 eth0
127.0.0.0 * 255.0.0.0 U 0 0 0 lo
224.0.0.0 * 240.0.0.0 U 0 0 0 eth0
If you don't see the line for multicast routing:
224.0.0.0 * 240.0.0.0 U 0 0 0 eth0
You will need to add in the next step. If you do see that line and the
problem is still there then contact the tao-users list by using
email. Please remember to use the problem form. It helps developers to
have a more educated guess at the exact problem you are having.
---------------------------------------
(Step 3)
You can do this manually in a script that start the Naming service:
(Linux/Unix):
/sbin/route add -net 224.0.0.0 netmask 240.0.0.0 dev eth0
Alternatively for RedHat users you can add this into a file
"/etc/sysconfig/static-routes". As of Redhat 7, you might have to
create this file, you can make an entry:
eth0 net 240.0.0.0 netmask 240.0.0.0
On startup when the network interfaces that will be supporting
multicast routing are started the route will be added. In my case it
adds multicasting routing to eth0 (the first NIC).
----------------------------------------
(Step 4)
Double check that the route has been added correctly using /sbin/route.
Kernel IP routing table
Destination Gateway Genmask Flags Metric Ref Use Iface
10.0.0.0 * 255.255.255.0 U 0 0 0 eth0
127.0.0.0 * 255.0.0.0 U 0 0 0 lo
224.0.0.0 * 240.0.0.0 U 0 0 0 eth0
At this point you should be able to run tao_cosnaming. Have fun!
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