CORBA Programming Reference

TP Framework

This topic includes the following sections:

The BEA Tuxedo CORBA TP Framework provides a programming TP Framework that enables users to create servers for high-performance TP applications. This chapter describes the TP Framework programming model and the TP Framework application programming interface (API) in detail. Additional information about how to use this API can be found in Creating CORBA Server Applications.

The TP Framework is required when developing BEA Tuxedo CORBA servers. Later releases will relax this requirement, though it is expected that most customers will use the TP Framework as an integral part of their applications.

BEA Tuxedo provides the infrastructure for providing load balancing, transactional capabilities, and administrative infrastructure. The base API used by the TP Framework is the CORBA API with BEA extensions. The TP Framework API is exposed to customers. The BEA Tuxedo ATMI is an optional API that can be mixed in with TP Framework APIs, allowing a customer to deploy distributed applications using a mix of CORBA servers and ATMI servers.

Before BEA Tuxedo CORBA, ORB products did not approach BEA Tuxedo's performance in large-scale environments. BEA Tuxedo systems support applications that can process hundreds of transactions per second. These applications are built using the BEA Tuxedo stateless-service programming model that minimizes the amount of system resources used for each request, and thus maximizes throughput and price performance.

Now, BEA Tuxedo CORBA and its TP Framework give customers a way to develop CORBA applications with performance similar to BEA Tuxedo ATMI applications. BEA Tuxedo CORBA servers provide throughput, response time, and price performance approaching the BEA Tuxedo stateless-service programming model, while using the CORBA programming model.

A Simple Programming Model

The TP Framework provides a simple, useful subset of the wide range of possible CORBA object implementation choices. You use it for the development of server-side object implementations only. When using any client-side CORBA ORB, clients interact with CORBA objects whose server-side implementations are managed by the TP Framework. Clients are unaware of the existence of the TP Framework—a client written to access a CORBA object executing in a non-BEA Tuxedo server environment will be able to access that same CORBA object executing in a BEA Tuxedo server environment without any changes or restrictions to the client interface.

The TP Framework provides a server environment and an API that is easier to use and understand than the CORBA Portable Object Adapter (POA) API, and is specifically geared towards enterprise applications. It is a simple server programming model and an orthodox implementation of the CORBA model, which will be familiar to programmers using ORBs such as ORBIX or VisiBroker.

The TP Framework simplifies the programming of BEA Tuxedo CORBA servers by reducing the complexity of the server environment in the following ways:

The TP Framework provides the following functionality:

Control Flow

The TP Framework, in conjunction with the ORB and the POA, controls the flow of the application program by doing the following:

Object State Management

The TP Framework API provides callback methods for application code to implement flexible state management schemes for CORBA objects. State management involves the saving and restoring of object state on object deactivation and activation. It also concerns the duration of activation of objects, which influences the performance of servers and their resource usage. The default duration of object activation is controlled by policies assigned to implementations at IDL compile time.

Transaction Integration

TP Framework transaction integration provides the following features:

Object Housekeeping

When a server is shut down, the TP Framework rolls back any transactions that the server is involved in and deactivates any CORBA objects that are currently active.

High-level Services

The TP interface in the TP Framework API provides methods for performing object registrations and utility functions. The following services are provided:

The purpose of these high-level service methods is to eliminate the need for developers to understand the CORBA POA, CORBA Naming Service, and BEA Tuxedo APIs, which they use for their underlying implementations. By encapsulating the underlying API calls with a high-level set of methods, programmers can focus their efforts on providing business logic rather than understanding and using the more complex underlying facilities.

State Management

State management involves the saving and restoring of object state on object deactivation and activation. It also concerns the duration of activation of objects, which influences the performance of servers and their resource usage. The external API of the TP Framework provides activate_object and deactivate_object methods, which are a possible location for state management code.

Activation Policy

State management is provided in the TP Framework by the activation policy. This policy controls the activation and deactivation of servants for a particular IDL interface (as opposed to the creation and destruction of the servants). This policy is applicable only to CORBA objects using the TP Framework.

The activation policy determines the default in-memory activation duration for a CORBA object. A CORBA object is active in a POA if the POA's active object map contains an entry that associates an object ID with an existing servant. Object deactivation removes the association of an object ID with its active servant. You can choose from one of three activation policies: method (the default), transaction, or process.

The activation policies are described below:

Application-controlled Activation and Deactivation

Ordinarily, activation and deactivation decisions are made by the TP Framework, as discussed earlier in this chapter. The techniques in this section show how to use alternate mechanisms. The application can control the timing of activation and deactivation explicitly for objects with particular policies.

Explicit Activation

Application code can bypass the on-demand activation feature of the TP Framework for objects that use the process activation policy. The application can "preactivate" an object (that is, activate it before any invocation) using the TP::create_active_object_reference call.

Preactivation works as follows. Before the application creates an object reference, the application instantiates a servant and initializes that servant's state. The application uses TP::create_active_object_reference to put the object into the Active Object Map (that is, associate the servant with an ObjectId). Then, when the first invocation is made, the TP Framework immediately directs the request to the process that created the object reference and then to the existing servant, bypassing the necessity to call Server::create_servant and then the servant's activate_object method (just as if this were the second or later invocation on the object). Note that the object reference for such an object will not be directed to another server and the object will never go through on-demand activation as long as the object remains activated.

Since the preactivated object has the process activation policy, it will remain active until one of two events occurs: (1) the ending of the process or (2) a TP::deactivateEnable call.

Usage Notes

Preactivation is especially useful if the application needs to establish the servant with an initial state in the same process, perhaps using shared memory to initialize state. Waiting to initialize state until a later time and in a potentially different process may be very difficult if that state includes pointers, object references, or complex data structures. TP::create_active_object_reference guarantees that the preactivated object is in the same process as the code that is doing the preactivation. While this is convenient, preactivation should be used sparingly, as should all process objects, because it preallocates precious resources. However, when needed and used properly, preallocation is more efficient than alternatives.

Examples of such usage might be an object using the "iterator" pattern. For example, there might a potentially long list of items that could be returned (in an unbound IDL sequence) from a "database_query" method (for example, the contents of the telephone book). Returning all such items in the sequence is impractical because the message size and the memory requirements would be too large.

On an initial call to get the list, an object using the iterator pattern returns only a limited number of items in the sequence and also returns a reference to an "iterator" object that can be invoked to receive further elements. This iterator object is initialized by the initial object; that is, the initial object creates a servant and sets its state to keep track of where in the long list of items the iteration currently stands (the pointer to the database, the query parameters, the cursor, and so forth).

The initial object preactivates this iterator object by using TP::create_active_object_reference. It also creates an object reference to that object to return to the client. The client then invokes repeatedly on the iterator object to receive, say, the next 100 items in the list each time. The advantage of preactivation in this situation is that the state might be complex. It is often easiest to set such state initially, from a method that has all the information in its context (call frame), when the initial object still has control.

When the client is finished with the iterator object, it invokes a final method on the initial object which deacativates the iterator object. The initial object deactivates the iterator object by invoking a method on the iterator object that calls the TP::deactivateEnable method, that is, the iterator object calls TP::deactivateEnable on itself.

Caution to Users

For objects to be preactivated in this fashion, the state usually cannot be recovered if a crash occurs. (This is because the state was considered too complex or inconvenient to set upon initial, delayed activation.) This is a valid object technique, essentially stating that the object is valid only for a single activation period.

However, a problem may arise because of the "one-time" usage. Since a client still holds an object reference that leads to the process containing that state, and since the state cannot be recreated after the crash, care must be taken that the client's next invocation does not automatically provoke a new activation of the object, because that object would have inapplicable state.

The solution is to refuse to allow the object to be activated automatically by the TP Framework. If the user provides the TobjS::ActivateObjectFailed exception to the TP Framework as a result of the activate_object call, the TP Framework will not complete the activation and will return an exception to the client, CORBA::OBJECT_NOT_EXIST. The client has presumably been warned about this possibility, since it knows about the iterator (or similar) pattern. The client must be prepared to restart the iteration.

Self Deactivation

Just as it is possible to preactivate an object with the process activation policy, it is possible to request the deactivation of an object with the process activation policy. The ability to preactivate and the ability to request deactivation are independent; regardless of how an object was activated, it can be deactivated explicitly.

A method in the application can request (via TP::deactivateEnable) that the object be deactivated. When TP::deactivateEnable is called and the object is subsequently deactivated, no guarantee is made that subsequent invocations on the CORBA object will result in reactivation in the same process as a previous activation. The association between the ObjectId and the servant exists from the activation of the CORBA object until one of the following events occurs: (1) the shutdown of the server process or (2) the application calls TP::deactivateEnable. After the association is broken, when the object is invoked again, it can be reactivated anywhere that is allowed by the BEA Tuxedo configuration parameters.

There are two forms of TP::deactivateEnable. In the first form (with no parameters), the object currently executing will be deactivated after completion of the method in which the call is made. The object itself makes the decision that it should be deactivated. This is often done during a method call that acts as a "signoff" signal.

The second form of TP::deactivateEnable allows a server to request deactivation of any active object, whether it is the object that is executing or not; that is, any part of the server can ask that the object be deactivated. This form takes parameters identifying the object to be deactivated. Explicit deactivation is not allowed for objects with an activation policy of transaction, because such objects cannot be safely deactivated until the end of a transaction.

In the TP::deactivateEnable call, the TP Framework calls the servant's deactivate_object method. Exactly when the TP Framework invokes deactivate_object depends on the state of the object to be deactivated. If the object is not currently in execution, the TP Framework deactivates it before returning to the caller. The object might be currently executing a method; this is always the case for TP::deactivateEnable with no parameters (since it refers to the currently executing object). In this case, TP::deactivateEnable is not told whether the object was deactivated immediately or not.

Servant Lifetime

A servant is a C++ class that contains methods to implement an IDL interface's operations. The user writes the servant code. The TP Framework invokes methods in the servant code to satisfy requests. The servant is created by the C++ "new" statement and is destroyed by the C++ "delete" statement. Exactly who does the creation and who does the deletion, and the timing of creation and deletion, is the subject of this section.

The Normal Case

In the normal case, the TP Framework completely controls the lifetime of a servant. The basic model is that, when a request for an inactive object arrives, the TP Framework obtains a servant and then activates it (by calling its activate_object method). At deactivation time, the TP Framework calls the servant's deactivate_object method and then disposes of the servant.

The phase "the TP Framework obtains a servant" means that when the TP Framework needs a servant to be created, it calls a user-written Server method, either Server::create_servant or ServerBase::create_servant_with_id. At that time, the application code must return a pointer to the requested servant. The application almost always does this by using the C++ "new" statement to create a new instance of a servant. The phrase "disposes of the servant" means that the TP Framework removes the reference to the servant, which actually deletes it.

The application must be aware that this current behavior of always creating and removing a servant may change in future versions of this product. The application should not depend on the current behavior, but should write servant code that allows reuse of a servant. Specifically, the servant code must work even if the servant has not been freshly created (by the C++ "new" statement). The TP Framework reserves the right not to remove a servant after it has been deactivated and then to reactivate it. This means that the servant must completely initialize itself at the time of the callback on the servant's activate_object method, not at the time of servant creation (not in the constructor).

Special Cases

There are two techniques an application can use to alter the normal TP Framework use of servants. The first has to do with obtaining a servant and the second has to do with disposing of the servant.

The application can alter the "obtaining" mechanism by using explicit preactivation. In this case, the application creates and initializes a servant before asking the TP Framework to declare it activated. Once such a servant has been turned over to the TP Framework (by the TP::create_active_object_reference call), that servant is treated by the TP Framework just like every other servant. The only difference is in its method of creation and initialization.

The application can alter the "disposing" mechanism by taking the responsibility for disposing of a servant instead of leaving that responsibility with the TP Framework. Once a servant is known to the TP Framework (through Server::create_servant, ServerBase::create_servant_with_id, or TP::create_active_object_reference), the TP Framework's default behavior is to remove that servant itself. In this case, the application code must no longer use references to the servant after deactivation.

However, the application may tell the TP Framework not to dispose of the servant after the TP Framework deactivates it. Taking responsibility for a servant is done on an individual servant basis, not for a whole class of servants, by calling Tobj_ServantBase::_add_ref with a parameter identifying the servant.

The advantage of the application taking responsibility for the servant is that the servant does not have to be created anew. If obtaining the servant is an expensive proposition, the application may choose to save the servant and reuse it later. This is especially likely to be true for servants for preactivated objects, but is true in general. For example, the next time the TP Framework makes a call on Server::create_servant or ServerBase::create_servant_with_id, the application might return a previously saved servant.

Additionally, once an application has taken responsibility for a servant, the application must take care to remove the servant (using Tobj_ServantBase::_remove_ref) when the servant is no longer needed, that is, when the reference count drops to zero, the same as for any other C++ instance. For more information about how the _remove_ref() method works, see Tobj_ServantBase::_remove_ref().

For more information on writing single-threaded and multithreaded server applications, see Creating CORBA Server Applications.

Saving and Restoring Object State

While CORBA objects are active, their state is contained in a servant. Unless an application uses TP::create_active_object_reference, state must be initialized when the object is first invoked (that is, the first time a method is invoked on a CORBA object after its object reference is created), and on subsequent invocations after they have been deactivated. While a CORBA object is deactivated, its state must be saved outside the process in which the servant was active. The object's state can be saved in shared memory, in a file, or in a database. Before a CORBA object is deactivated, its state must be saved, and when it is activated, its state must be restored.

The programmer determines what constitutes an object's state and what must be saved before an object is deactivated, and restored when an object is activated.

Note On Use of Constructors and Destructors for CORBA Objects

The state of CORBA objects must not be initialized, saved, or restored in the constructors or destructors for the servant classes. This is because the TP Framework may reuse an instance of a servant rather than deleting it at deactivation. No guarantee is made as to the timing of the creation and deletion of servant instances.

Transactions

The following sections provide information about transaction policies and how to use transactions.

Transaction Policies

Eligibility of CORBA objects to participate in global transactions is controlled by the transaction policies assigned to implementations at compile time. The following policies can be assigned.

Transaction Initiation

Transactions are initiated in one of two ways:

Transaction Termination

In general, the handling of the outcome of a transaction is the responsibility of the initiator. Therefore, the following are true:

The following behavior is enforced by the BEA Tuxedo system:

Transaction Suspend and Resume

The CORBA object must follow strict rules with respect to suspending and resuming a transaction within a method invocation. These rules and the error conditions that result from their violation are described below.

When a CORBA object method begins execution, it can be in one of the following three states with respect to transactions:

Restrictions on Transactions

The following restrictions apply to BEA Tuxedo CORBA transactions:

SQL and Global Transactions

Adhere to the following guidelines when using SQL and Global Transactions:

Voting on Transaction Outcome

CORBA objects can affect transaction outcome during two stages of transaction processing:

Transaction Timeouts

When a transaction timeout occurs, the transaction is marked so that the only possible outcome is to roll back the transaction, and the CORBA::TRANSACTION_ROLLEDBACK standard exception is returned to the client. Any attempts to send new requests will also fail with the CORBA::TRANSACTION_ROLLEDBACK exception until the transaction has been aborted.

IIOP Client Failover

It is not always possible to determine when a server instance failed with respect to the work it was doing at the time of failure. For example, if a server instance fails after handling a client request but before returning the response, there is no way to tell that the request was handled. A user that does not get a response will most likely retry, resulting in an additional request.

Support for IIOP client failover has been added to BEA Tuxedo CORBA as an availability enhancement. IIOP client failover provides a transparent mechanism for a CORBA remote client to automatically connect to an alternative ISL and then retry the request in case of failure.

IIOP client failover marks an interface implementation as idempotent. An idempotent implementation is one that can be repeated without any negative side-effects. For example, SET BALANCE.

Setting The Retry Policy

In order to mark an interface implementation as idempotent, you must set the retry policy in the implementation configuration file (ICF) using the retry_policy option. For a description of the ICF, refer to the Implementation Configuration File (ICF) section.

The retry_policy option has two settings:

MIB Support

You can also check the retry policy using the TA_RTPOLICY attribute added to the MIB(5) T_IFQUEUE and T_INTERFACE classes. The TA_RTPOLICY attribute value is either never or always.

Initiating IIOP Client Failover

To initiate IIOP client failover support, ISL servers must be specified using the -C warn|none option in the *SERVERS section of the UBBCONFIG file

This option allows ISL to accept unofficial connection directly from the client orb. ISL servers that are not specified using the -C warn|none option will not be placed in candidate IIOP gateway pools. Consequently, the client will not failover to those ISL servers.

In the following UBBCONFIG file example, the ISL servers specified in lines 1 and 2 will support client failover. The ISL server in line 3 will not.

*SERVERS

	ISL SRVGRP=SYS_GRP1 SRVID=10 CLOPT="-A -- -C warn -n //myhost1:2468"

	ISL SRVGRP=SYS_GRP2 SRVID=20 CLOPT="-A -- -C none -n //myhost2:2469"

	ISL SRVGRP=SYS_GRP3 SRVID=30 CLOPT="-A -- -n //myhost3:2470"

IIOP Client Failover Limitations

IIOP Client Failover is not supported under the following three instances:

See Also

Weblogic CORBA Clustering and Load Balancing Support

Tuxedo CORBA C++ client supports failover to Weblogic clustering servers and also supports load balancing. For more information, see WebLogic 9.1 documentation - Failover and Replication in a Cluster and Load Balancing in a Cluster.

Parallel Objects

Support for parallel objects was added to BEA Tuxedo CORBA in release 8.0 as a performance enhancement. The parallel objects feature enables you to designate all business objects in a particular application as stateless objects. The effect is that, unlike stateful business objects, which can only run on one server in a single domain, stateless business objects can run on all servers in a single domain. Thus, the benefits of parallel objects are as follows:

For more information on parallel objects, see Scaling, Distributing, and Tuning CORBA Applications.

To implement parallel objects, the concurrency policy option has been added to the ICF file. To select parallel objects for a particular application, you set the concurrency policy option to user-controlled. When you select user-controlled concurrency, the business object are not registered with the Active Object Map (AOM) and, therefore, are stateless and can be active on more than one server at a time. Thus, these objects are referred to as parallel objects.

If user-controlled concurrency is selected, the servant implementation must comply with one of the following statements:

In release 8.0 of the BEA Tuxedo software, the Implementation Configuration File (ICF) was modified to support user-controlled concurrency. In Listing 3-2, the changes to add this support are highlighted in bold type. For a description of the ICF syntax, see ICF Syntax.

[#pragma activation_policy method|transaction|process]
[#pragma transaction_policy never|ignore|optional|always]
[#pragma concurrency_policy user_controlled|system_controlled]
[Module module-name {]
   implementation [implementation-name]
     {
     implements (module-name::interface-name);
     [activation_policy (method|transaction|process);]
     [transaction_policy (never|ignore|optional|always);]
     [concurrency_policy (user_controlled|system_controlled);]
     };
  [};]

User-controlled concurrency can be used with factory-based routing, all activation policies, and all transaction policies. The interaction with these features is as follows:

TP Framework API

This section describes the TP Framework API. Additional information about how to use this API can be found in Creating CORBA Server Applications.

The TP Framework comprises the following components:

The visible part of the TP Framework consists of two categories of operations:

Server Interface

The Server interface provides callback methods that can be used for application-specific server initialization and termination logic. This interface also provides a callback method that is used to create servants when servants are required for object activation.

The Server interface has the following characteristics:

For a description of the Server interface methods, see ServerBase Interface.

C++ Declarations

For the C++ mappings, seeServerBase Interface.

ServerBase Interface

The serverBase interface allows you to take full advantage of multithreading capabilities. You can create your own Server classes that inherit from the ServerBase class. This provides you with the following:

The ServerBase class provides the same operations that were available in the Server class in earlier releases. The Server class inherits from the ServerBase class.

These methods can be used with single-threaded and multithreaded applications:

These methods can be used with multithreaded server applications only:

C++ Declarations (in Server.h)

The C++ mapping is as follows:

class OBBEXPDLLUSER ServerBase {
public:

    virtual CORBA::Boolean
        initialize(int argc, char** argv) = 0;

    virtual void
        release() = 0;

    virtual Tobj_Servant
        create_servant(const char* interfaceName) = 0;

       // Default Implementations Supplied
       virtual Tobj_Servant
           create_servant_with_id(const char* interfaceName,
                                   const char* stroid);

       virtual CORBA::Boolean
           thread_initialize(int argc, char** argv);

       virtual void
           thread_release();

};

class Server : public ServerBase {
public:

    CORBA::Boolean initialize(int argc, char** argv);
    void release();
    Tobj_Servant create_servant(const char* interfaceName);
};

Server::create_servant()

Synopsis

Creates a servant to instantiate a C++ object.

C++ Binding

class Server {
public:
      Tobj_Servant     create_servant(const char* interfaceName);
};

Argument

interfaceName

Exception

If an exception is thrown in Server::create_servant(), the TP Framework catches the exception. Activation fails. A CORBA::OBJECT_NOT_EXIST() exception is raised back to the client. In addition, an error message is written to the user log (ULOG) file, as follows, for each exception type:

TobjS::CreateServantFailed

TobjS::OutOfMemory

CORBA::Exception

Other Exception

Description

The create_servant method is invoked by the TP Framework when a request arrives at the server and there is no available servant to satisfy the request. The TP Framework calls the create_servant method with the interface name for the servant to be created. The server application instantiates an appropriate C++ object and returns a pointer to it. Typically, the method contains a switch statement on the interface name and creates a new object, depending on the interface name.

Return Value

Tobj_Servant

ServerBase::create_servant_with_id()

Synopsis

Creates a servant for this target object. This method supports the development of single-headed and multithreaded server applications.

C++ Binding

Tobj_Servant create_servant_with_id (const char* interfaceName,
                                     const char* stroid);

Arguments

interfaceName

stroid

Description

The TP Framework invokes the create_servant_with_id method when a request arrives at the server and there no servant is available to satisfy the request. The TP Framework passes in the interface name for the servant to be created and the object ID associated with the object with which the servant will be associated. The server application instantiates an appropriate C++ object and returns a pointer to it. Typically, the method contains a switch statement on the interface name and creates a new object, depending on the interface name. Providing the object ID allows a servant implementation to make decisions during the creation of the servant instance that require knowledge of the target object. Reentrancy support is one example of how a servant implementation might employ knowledge of the target object.

The ServerBase class provides a default implementation of create_servant_with_id which calls the standard create_servant method passing the interface name. This default implementation ignores the target object ID parameter.

Return Value

Tobj_Servant

Example

Tobj_Servant simple_per_request_server::create_servant_with_id(
const char* intf_repos_id, const char* stroid)
{
TP::userlog("create_servant_with_id called in thread %ld",
(unsigned long)SIMPTHR_GETCURRENTTHREADID);

// Perform any necessary initialization based on
// this object ID

return create_servant(intf_repos_id);
}

Server::initialize()

Synopsis

Allows the application to perform application-specific initialization procedures, such as logging into a database, creating and registering well-known object factories, initializing global variables, and so forth.

C++ Binding

class Server {
public:

        CORBA::Boolean  initialize(int argc, char** argv);

};

Arguments

The argc and argv arguments are passed from the command line. The argc argument contains the name of the server. The argv argument contains the first command-line option that is specific to the application, if there are any.

Command-line options are specified in the UBBCONFIG file using the CLOPT parameter in the entry for the server in the SERVERS section. System-recognized options come first in the CLOPT parameter, followed by a double-hyphen (--), followed by the application-specific options. The value of argc is one greater than the number of application-specific options. For details, see ubbconfig(5) in the File Formats, Data Descriptions, MIBs, and System Processes Reference.

Exceptions

If an exception is raised in Server::initialize(), the TP Framework catches the exception. The TP Framework behavior is the same as if initialize() returned FALSE (that is, an exception is considered to be a failure). In addition, an error message is written to the user log (ULOG) file, as follows, for each exception type:

TobjS::InitializeFailed

CORBA::Exception

Other Exceptions

Description

The initialize callback method, which is invoked as the last step in server initialization, allows the application to perform application-specific initialization.

Typically, a server application does the following tasks in Server::initialize:

It is the responsibility of the server application to open any required XA resource managers. This is done by invoking either of the following methods:

Return Value

Boolean TRUE or FALSE. TRUE indicates success. FALSE indicates failure. If an error occurs in initialize(), the application code should return FALSE. The application code should not call the system call exit(). Calling exit() does not give the TP Framework a chance to release resources allocated during startup and may cause unpredictable results.

If the return value is FALSE:

ServerBase::thread_initialize()

Synopsis

Performs any necessary application-specific initialization for a thread created using the BEA Tuxedo software. This method supports the development of a multithreaded server application.

C++ Binding

CORBA::Boolean thread_initialize(int argc, char** argv)

Arguments

argc

argv

Description

In managing the thread pool, the BEA Tuxedo software creates and releases threads using the operating system thread library services. Depending on application requirements, these threads might need to be initialized before they are used to process requests.

The thread_initialize callback method is invoked each time a thread is created, to initialize the thread. Note that the BEA Tuxedo software manages a number of system-owned threads that are used for dispatching requests; these system-owned threads are in addition to those threads in the thread pool. Under some circumstances the servant methods you implement are also executed in these system-owned threads; for this reason the BEA Tuxedo software invokes the thread_initialize method to initialize the system-owned threads.

The ServerBase class provides a default implementation of the thread_initialize method that opens the XA resource manager in the initialized thread.

Return Value

CORBA::Boolean

Example

CORBA::Boolean simple_per_request_server::thread_initialize(
int argc, char** argv)
{
TP::userlog("thread_initialize called in thread %ld",
(unsigned long)SIMPTHR_GETCURRENTTHREADID);
return CORBA_TRUE;
}

Server::release()

Synopsis

Allows the application to perform any application-specific cleanup, such as logging off a database, unregistering well-known factories, or deallocating resources.

C++ Binding

typedef Tobj_ServantBase* Tobj_Servant;

class Server {
public:
        void      release();
};

Arguments

None.

Exceptions

If an exception is raised in release(), the TP Framework catches the exception. Each exception causes an error message to be written to the user log (ULOG) file, as follows:

TobjS::ReleaseFailed

CORBA::Exception

Other Exceptions

In all cases, the server continues to exit.

Description

The release callback method, which is invoked as the first step in server shutdown, allows the server application to perform any application-specific cleanup. The user must override the virtual function definition.

Typical tasks performed by the application in this method are as follows:

This method is normally called in response to a tmshutdown command from the administrator or operator.

The TP Framework provides a default implementation of Server::release(). The default implementation closes XA resource managers for the server. The implementation does this by issuing a tx_close() invocation, which uses the default CLOSEINFO configured for the server's group in the UBBCONFIG file.

It is the responsibility of the application to close any open XA resource managers. This is done by issuing either of the following calls:

Return Value

None.

ServerBase::thread_release()

Synopsis

Performs application-specific cleanup when a thread that was created by the BEA Tuxedo software is released. This method supports the development of a multithreaded server application.

C++ Binding

void thread_release()

Arguments

None.

Description

The thread_release callback method is invoked each time a thread is released. Implement the thread_release method as necessary to perform application-specific resource cleanup.

The ServerBase class provides a default implementation of the thread_release method that closes the XA resource manager in the released thread.

Return Value

None.

Example

void simple_per_request_server::thread_release()
{
TP::userlog("thread_release called in thread %ld",
(unsigned long)SIMPTHR_GETCURRENTTHREADID);
}

Tobj_ServantBase Interface

The Tobj_ServantBase interface inherits from the PortableServer::RefCountServantBase class and defines operations that allow a CORBA object to assist in the management of its state in a thread-safe manner. Every implementation skeleton generated by the IDL compiler automatically inherits from the Tobj_ServantBase class. The Tobj_ServantBase class contains two virtual methods, activate_object() and deactivate_object(), that may be optionally implemented by the programmer.

Whenever a request comes in for an inactive CORBA object, the object is activated and the activate_object() method is invoked on the servant. When the CORBA object is deactivated, the deactivate_object() method is invoked on the servant. The timing of deactivation is driven by the implementation's activation policy. When the deactivate_object() method is invoked, the TP Framework passes in a reason code to indicate why the call was made.

These methods support the development of a multithreaded server application:

C++ Declaration (in Tobj_ServantBase.h)

The C++ mapping for the Tobj_servantBase interface is as follows:

class Tobj_ServantBase : public PortableServer::RefCountServantBase {
public:

    Tobj_ServantBase& operator=(const Tobj_ServantBase&);
    Tobj_ServantBase() {}
    Tobj_ServantBase(const Tobj_ServantBase& s) :
        PortableServer::RefCountServantBase(s) {}

    virtual void activate_object(const char *) {}

    virtual void deactivate_object(const char*, 
        TobjS::DeactivateReasonValue) {}

    virtual CORBA::Boolean _is_reentrant() { return CORBA_FALSE; }
};

typedef Tobj_ServantBase * Tobj_Servant;

Tobj_ServantBase:: activate_object()

Synopsis

Associates an object ID with a servant. This method gives the application an opportunity to restore the object's state when the object is activated. The state may be restored from shared memory, from an ordinary flat file, or from a database file.

C++ Binding

class Tobj_ServantBase : public PortableServer::ServantBase {
public:	
        virtual void activate_object(const char * stroid) {}
};

Argument

stroid

Description

Object activation is triggered by a client invoking a method on an inactive CORBA object. This causes the Portable Object Adapter (POA) to assign a servant to the CORBA object. The activate_object() method is invoked before the method invoked by the client is invoked. If activate_object() returns successfully, that is, without raising an exception, the requested method is executed on the servant.

The activate_object() and deactivate_object() methods and the method invoked by the client can be used by the programmer to manage object state. The particular way these methods are used to manage object state may vary according to the needs of the application. For a discussion of how these methods might be used, see Creating CORBA Server Applications.

If the object is currently infected with a global transaction, activate_object() executes within the scope of that same global transaction.

It is the responsibility of the programmer of the object to check that the stored state of the object is consistent. In other words, it is up to the application code to save a persistent flag that indicates whether or not deactivate_object() successfully saved the state of the object. That flag should be checked in activate_object().

Return Value

None.

Exceptions

If an error occurs while executing activate_object(), the application code should raise either a CORBA standard exception or a TobjS::ActivateObjectFailed exception. When an exception is raised, the TP Framework catches the exception, and the following events occur:

TobjS::ActivateObjectFailed

TobjS::OutOfMemory

CORBA::Exception

Other exception

Tobj_ServantBase::_add_ref()

Synopsis

Adds a reference to a servant. This method supports the development of a multithreaded server application.

C++ Binding

void _add_ref()

Arguments

None.

Description

Invoke this method when a reference to a servant is needed. Invoking this method causes the reference count for the servant to increment by one.

Return Value

None.

Example

myServant * servant = new intf_i();
if(servant != NULL)
   servant->_add_ref();

Tobj_ServantBase::deactivate_object()

Synopsis

Removes the association of an object ID with its servant. This method gives the application an opportunity to save all or part of the object's state before the object is deactivated. The state may be saved in shared memory, in an ordinary flat file, or in a database file.

C++ Binding

class Tobj_ServantBase : public PortableServer::ServantBase {
public:	
        virtual void deactivate_object(const char* stroid,
                       TobjS::DeactivateReasonValue  reason) {}
};

Arguments

stroid

reason

Description

Object deactivation is initiated either by the system or by the application, depending on the activation policy of the implementation for the CORBA object. The deactivate_object() method is invoked before the CORBA object is deactivated. For details of these policies and their use, see the section ICF Syntax.

Deactivation may occur after an execution of a method invoked by a client if the activation policy for the CORBA object implementation is method, or as a result of the end of transactional work if the activation policy is transaction. It may also occur as the result of server shutdown if the activation policy is transaction or process.

In addition, the BEA Tuxedo software supports the use of user-controlled deactivation of CORBA objects having an activation policy of process or method via the use of the TP::deactivateEnable() and TP::deactivateEnable(-,-,-) methods. TP::deactivateEnable can be called inside a method of an object to cause the object to be deactivated at the end of the method. If TP::deactivateEnable is called in an object with the transaction activation policy, an exception is raised (TobjS::IllegalOperation) and the TP Framework takes no action. TP::deactivateEnable(-,-,-) can be called to deactivate any object that has a process activation policy. For more information, see the section TP::deactivateEnable().

The activate_object() and deactivate_object() methods and explicit methods invoked by the client can be used by the programmer to manage object state. The manner in which these methods are used to manage object state may vary according to the needs of the application. For a discussion of how these methods might be used, see Creating CORBA Server Applications.

The CORBA object with transaction activation policy gets to vote on the outcome of the transaction when the deactivate_object() method is invoked with the DR_TRANS_COMMITTING reason code. By calling Current.rollback_only() the method can force the transaction to be rolled back; otherwise, the two-phase commit algorithm continues. The transaction will not necessarily be committed just because Current.rollback_only() is not called in this method. Any other CORBA object or resource manager involved in the transaction could also vote to roll back the transaction.

Restriction

Note that if the object is involved in a transaction when this method is invoked, there are restrictions on what type of processing can be done based on the reason the object is invoked. If the object was involved in a transaction, the activation policy is transaction and the reason code for the call is:

DR_TRANS_ABORTED

DR_TRANS_COMMITTING

The reason for these restrictions is that the deactivation of objects with activation policy transaction is controlled by a call to the TP Framework from the transaction manager for the transaction. When the call with reason code DR_TRANS_COMMITTING is made, the transaction manager is executing phase 1 (prepare) of the two-phase commit. At this stage, it is not possible to issue a call to suspend a transaction nor to initiate a new transaction. Since a call to a CORBA object that was in another process would require that process to join the transaction, and the transaction manager is already executing the prepare phase, this would cause an error¹. Since a call to a CORBA object that had no transactional properties would require that the current transaction be suspended, this would also cause an error. The same is true of a tpcall().

Similarly, when the invocation with reason code DR_TRANS_ABORTED is made, the transaction manager is already aborting. While the transaction manager is aborting, it is not possible to either suspend a transaction or initiate a new transaction. The same restrictions apply as for DR_TRANS_COMMITTING.

Return Value

None.

Exceptions

If the CORBA object method that is invoked by the client raises an exception, that exception is caught by the TP Framework and is eventually returned to the client. This is true even if deactivate_object() is invoked and raises an exception.

The client will never be notified about exceptions that are raised in deactivate_object(). It is the responsibility of the application code to check that the stored state of the CORBA object is consistent. For example, the application code could save a persistent flag that indicates whether or not deactivate_object() successfully saved the state. That flag can then be checked in activate_object().

If an error occurs while executing deactivate_object(), the application code should raise either a CORBA standard exception or a DeactivateObjectFailed exception. If deactivate_object() was invoked by the TP Framework, the TP Framework catches the exception and the following events occur:

TobjS::DeactivateObjectFailed

CORBA::Exception

Other exception

Tobj_ServantBase::_is_reentrant()

Synopsis

Indicates that the object supports concurrent, reentrant invocations. This method supports the development of a multithreaded server application.

C++ Binding

CORBA::Boolean _is_reentrant()

Arguments

None.

Description

The BEA Tuxedo server infrastructure calls this method to determine whether the servant implementation supports a reentrant invocation. To support reentrancy, a servant must include the necessary code to protect the integrity of its state while multiple threads interact with the object.

The Tobj_ServantBase class provides a default implementation of the _is_reentrant method that returns FALSE.

Return Value

CORBA::Boolean

Example

CORBA::Boolean Simple_i::_is_reentrant()
{ TP::userlog("_is_reentrant called in thread %ld",
(unsigned long)SIMPTHR_GETCURRENTTHREADID);
return CORBA_TRUE;
}

Tobj_ServantBase::_remove_ref()

Synopsis

Releases a reference to a servant. This method supports the development of a multithreaded server application.

C++ Binding

void _remove_ref()

Parameters

None.

Description

Invoke this method when a reference to a servant is no longer needed. Invoking this method causes the reference count for the servant to be decremented by one. If the _remove_ref() method brings the reference count to zero, it also calls the C++ "delete" statement on its own this pointer and deletes the servant.

Return Value

None.

Example

if(servant != NULL)
   servant->_remove_ref();

TP Interface

The TP interface supplies a set of service methods that can be invoked by application code. This is the only interface in the TP Framework that can safely be invoked by application code. All other interfaces have callback methods that are intended to be invoked only by system code.

The purpose of this interface is to provide high-level calls that application code can call, instead of calls to underlying APIs provided by the Portable Object Adapter (POA), the CORBA Naming Service, and the BEA Tuxedo system. By using these calls, programmers can learn a simpler API and are spared the complexity of the underlying APIs. The TP interface implicitly uses two features of the BEA Tuxedo software that extend the CORBA APIs:

For information about the FactoryFinder object, see the section FactoryFinder Interface. For more information about factory-based routing, see Setting Up a BEA Tuxedo Application.

Usage Notes

C++ Declarations (in TP.h)

The C++ mapping is as follows:

class TP {
public:
   static CORBA::Object_ptr  create_object_reference(
                                  const char*    interfaceName, 
                                  const char*   stroid,
                                  CORBA::NVList_ptr criteria);
   static CORBA::Object_ptr  create_active_object_reference(	
                                  const char*  interfaceName, 
                                  const char* stroid,
                                  Tobj_Servant servant);
   static CORBA::Object_ptr  get_object_reference();	
   static void               register_factory(
                                  CORBA::Object_ptr factory_or, 
                                  const char*       factory_id);
   static void               unregister_factory(
                                  CORBA::Object_ptr factory_or,
                                  const char*       factory_id);
   static void               deactivateEnable()
   static void               deactivateEnable(
                                  const char*  interfaceName,
                                  const char* stroid,
                                  Tobj_Servant servant);
   static CORBA::ORB_ptr     orb();
   static Tobj_Bootstrap*    bootstrap();
   static void               open_xa_rm();
   static void               close_xa_rm();
   static int                userlog(char*, ... );
   static char*                 get_object_id(CORBA::Object_ptr obj);
   static void               application_responsibility(
                                 Tobj_Servant servant);
};

TP::application_responsibility()

Synopsis

Tells the TP Framework that the application is taking responsibility for the servant's lifetime.

C++ Binding

static void application_responsibility(Tobj_Servant servant);

Arguments

servant

Exceptions

TobjS::InvalidServant

Description

This method tells the TP Framework that the application is taking responsibility for the servant's lifetime. As a result of this call, when the TP Framework has completed deactivating the object (that is, after invoking the servant's deactivate_object method), the TP Framework does nothing more with the object.

Once an application has taken responsibility for a servant, the application must take care to delete servant when it is no longer needed, the same as for any other C++ instance.

If the servant is not known to the TP Framework (that is, it is not active), this call has no effect.

Return Values

None.

TP::bootstrap()

Synopsis

Returns a pointer to a Tobj::Tobj_Bootstrap object. The Bootstrap object is used to access initial object references for the FactoryFinder object, the Interface Repository, the TransactionCurrent, and the SecurityCurrent objects.

C++ Binding

static Tobj_Bootstrap* TP::bootstrap();

Arguments

None.

Return Value

Upon successful completion, bootstrap() returns a pointer to the Tobj::Tobj_Bootstrap object that is created by the TP Framework when the server application is started.

Exceptions

None.

Description

The TP Framework creates a Tobj::Tobj_Bootstrap object as part of initialization; it is not necessary for the application code to create any other Tobj::Tobj_Bootstrap objects in the server.

TP::close_xa_rm()

Synopsis

Closes the XA resource manager to which the invoking process is linked.

C++ Binding

static void TP::close_xa_rm ();

Arguments

None.

Description

The close_xa_rm() method closes the XA resource manager to which the invoking process is linked. XA resource managers are provided by database vendors, such as Oracle and Informix.

This method should be invoked once from the Server::release() method for each server that is involved in global transactions. This includes servers that are linked with an XA resource manager, as well as servers that are involved in global transactions, but are not actually linked with an XA-compliant resource manager.

The close_xa_rm() method should be invoked in place of a close invocation that is specific to the resource manager. Because resource managers differ in their initialization semantics, the specific information needed to close a particular resource manager is placed in the CLOSEINFO parameter in the GROUPS section of the BEA Tuxedo system UBBCONFIG file.

The format of the CLOSEINFO string is dependent on the requirements of the database vendor providing the underlying resource manager. For more information about the CLOSEINFO parameter, see Setting Up a BEA Tuxedo Application and the ubbconfig(5) reference page in the File Formats, Data Descriptions, MIBs, and System Processes Reference. Also, refer to database vendor documentation for information about how to develop and install applications that use the XA libraries.

Return Values

None.

Exceptions

CORBA::BAD_INV_ORDER

Tobj::RMFailed

TP::create_active_object_reference()

Synopsis

Creates an object reference and preactivates an object.

C++ Binding

static CORBA::Object_ptr
    create_active_object_reference(
           const char*       interfaceName, 
           const char*      stroid,
           Tobj_Servant     servant);

Arguments

interfaceName

stroid

servant

Exceptions:

TobjS::InvalidInterface

TobjS::InvalidObjectId

TobjS::ServantAlreadyActive

TobjS::ObjectAlreadyActive

TobjS::IllegalOperation

Description

This method creates an object reference and preactivates an object. The resulting object reference may be passed to clients who will use it to access the object.

Ordinarily, the application will call this method in two places:

This method allows an application to activate an object explicitly before its first invocation. (For reasons you might want to do this, refer to the section Explicit Activation.) The user first creates a servant and sets its state before calling create_active_object_reference. The TP Framework then enters the servant and string ObjectId in the Active Object Map. The result is exactly the same as if the TP Framework had previously invoked Server::create_servant, received back the servant pointer, and then had invoked servant::activate_object.

The object so activated must be for an interface that was declared with the process activation policy; otherwise, an exception is raised.

If the object is deactivated, an object reference held by a client might cause the object to be activated again in some other process. For a discussion about situations in which this might be a problem, refer to the section Explicit Activation.

Caution

When you preactivate objects in an interface, you must specify an activation policy of process in the ICF file for that interface. However, when you specify the process activation policy for an interface in the ICF file, this can lead to the following problem.

Problem Statement

Workaround

You can avoid this problem by having the administrator configure SERVER1 and SERVER2 in different groups. The administrator uses the SERVERS section of the UBBCONFIG file to define groups.

Return Value

The newly created object reference.

TP::create_object_reference()

Synopsis

Creates an object reference. The resulting object reference may be passed to clients who use it to access the object.

C++ Binding

static CORBA::Object_ptr    TP::create_object_reference (
                               const char* interfaceName,
                               const char* stroid,
                               CORBA::NVList_ptr criteria);

Arguments

interfaceName

stroid

criteria

Exceptions

The following exceptions can be raised by the create_object_reference() method:

InvalidInterface

InvalidObjectId

Description

The server application is responsible for invoking the create_object_reference() method. This method creates an object reference. The resulting object reference may be passed to clients who will use it to access the object.

Ordinarily, the server application calls this method in two places:

For examples of how and when to call the create_object_reference() method, see Creating CORBA Server Applications.

Return Value

Object

Example

The following example shows how to use the criteria argument:

CORBA::NVList_ptr criteria;
CORBA::Long branch_id = 7;
CORBA::Long account_id = 10001;
CORBA::Any any_val;

// Create the list and assign to _var to cleanup on exit
CORBA::ORB::create_list (2, criteria);
CORBA::NVList_var criteria_var(criteria);

// Add the BRANCH_ID
any_val <<= branch_id;
criteria->add_value("BRANCH_ID", any_val, 0);

// Add the ACCOUNT_ID
any_val <<= account_id;
criteria->add_value("ACCOUNT_ID", any_val, 0);

// Create the object reference.
TP::create_object_reference ("IDL:BankApp/Teller:1.0",
"Teller_01", criteria);

TP::deactivateEnable()

Synopsis

Enables application-controlled deactivation of CORBA objects.

C++ Binding

Current-object format:

static void           TP::deactivateEnable();

Any-object format:

static void        TP::deactivateEnable(
                           const char*  interfaceName,
                           const char* stroid,
                            Tobj_Servant servant);

Arguments

interfaceName

stroid

servant

Exceptions

The following exceptions can be raised by the deactivateEnable() method:

IllegalOperation

TobjS::ObjectNotActive

Description

This method can be used to cause deactivation of an object, either the object currently executing (upon completion of the method in which it is called) or another object. It can only be used for objects with the process activation policy. It provides additional flexibility for objects with the process activation policy.

Depending on which of the overloaded functions are called, the actions are as follows.

Current-object format

Any-object format

If the object for which the deactivate is requested has a transaction activation policy, an IllegalOperation exception is raised. This is because deactivation of such objects may interfere with their correct notification of transaction completion by the BEA Tuxedo transaction manager.

Return Value

None.

TP::get_object_id ()

Synopsis

Allows a server to retrieve the string ObjectId contained in an object reference that was created in the TP Framework.

C++ Binding

char* TP::get_object_id(Corba::Object_ptr obj);

Arguments

obj

The object reference from which to get the ObjectId.

Exception

TobjS::InvalidObject

Description

This method allows a server to retrieve the string ObjectId contained in an object reference that was created in the TP Framework. If the object reference was not created in the TP Framework (for example, it was created by a client ORB), an exception is raised.

The caller must call CORBA::string_free on the returned value when the object reference is no longer needed.

Return Value

The string ObjectId passed to TP::create_object_reference or TP::create_active_object_reference when the object reference was created.

TP::get_object_reference()

Synopsis

Returns a pointer to the current object.

C++ Binding

static CORBA::Object_ptr  TP::get_object_reference ();

Arguments

None.

Note that if get_object_reference() is invoked from within either Server::initialize() or Server::release(), it is considered to be invoked outside the scope of an application's TP object execution; therefore, the TobjS::NilObject exception is raised.

Exceptions

The following exception can be raised by the get_object_reference() method:

NilObject

Description

This method returns a pointer to the current object. The CORBA::Object_ptr pointer that is returned can be passed to a client.

Return Value

The get_object_reference() method returns a CORBA::Object_ptr for the current object when invoked within the scope of a CORBA object execution. Otherwise, the TobjS::NilObject exception is raised.

TP::open_xa_rm()

Synopsis

Opens the XA resource manager to which the invoking process is linked.

C++ Binding

static void TP::open_xa_rm();

Arguments

None.

Exceptions

Tobj::RMFailed

Description

The open_xa_rm() method opens the XA resource manager to which the invoking process is linked. XA resource managers are provided by database vendors, such as Oracle and Informix.

This method should be invoked once from the Server::initialize() method for each server that participates in a global transaction. This includes servers that are linked with an XA resource manager, as well as servers that participate in a global transaction, but are not actually linked with an XA-compliant resource manager.

The open_xa_rm() method should be invoked in place of an open invocation that is specific to a resource manager. Because resource managers differ in their initialization semantics, the specific information needed to open a particular resource manager is placed in the OPENINFO parameter in the GROUPS section of the UBBCONFIG file.

The format of the OPENINFO string is dependent on the requirements of the database vendor providing the underlying resource manager. For more information about the CLOSEINFO parameter, see Setting Up a BEA Tuxedo Application and the ubbconfig(5) reference page in the File Formats, Data Descriptions, MIBs, and System Processes Reference. Also, refer to database vendor documentation for information about how to develop and install applications that use the XA libraries.

Return Values

None.

TP::orb()

Synopsis

Returns a pointer to an ORB object.

C++ Binding

static CORBA::ORB_ptr TP::orb();

Arguments

None.

Exceptions

None.

Description

Access to the ORB object allows the application to invoke ORB operations, such as string_to_object() and object_to_string().

Return Value

Upon successful completion, orb() returns a pointer to the ORB object that is created by the TP Framework when the server program is started.

TP::register_factory()

Synopsis

Locates the BEA Tuxedo FactoryFinder object and registers a BEA Tuxedo factory.

C++ Binding

static void TP::register_factory(
              CORBA::Object_ptr factory_or, const char* factory_id);

Arguments

factory_or

factory_id

Exceptions

The following exceptions can be raised by the register_factory() method:

TobjS::CannotProceed

TobjS::InvalidName

TobjS::InvalidObject

TobjS::RegistrarNotAvailable

TobjS::OverFlow

Description

This method locates the BEA Tuxedo FactoryFinder object and registers a BEA Tuxedo factory. Typically, TP::register_factory() is invoked from Server::initialize() when the server creates its factories. The register_factory() method locates the BEA Tuxedo FactoryFinder object and registers the BEA Tuxedo factory.

Return Value

None.

TP::unregister_factory()

Synopsis

Locates the BEA Tuxedo FactoryFinder object and removes a factory.

C++ Binding

static void TP::unregister_factory (
               CORBA::Object_ptr factory_or, const char* factory_id);

Arguments

factory_or

factory_id

Exceptions

The following exceptions can be raised by the unregister_factory() method:

CannotProceed

InvalidName

RegistrarNotAvailable

TobjS::OverFlow

Description

This method locates the BEA Tuxedo FactoryFinder object and removes a factory. Typically TP::unregister_factory() is invoked from Server::release() to unregister server factories.

Return Value

None.

TP::userlog()

Synopsis

Writes a message to the user log (ULOG) file.

C++ Binding

static int    TP::userlog(char*, ...);

Arguments

The first argument is a printf(3S) style format specification. The printf(3S) argument is described in a C or C++ reference manual.

Exceptions

None.

Description

The userlog() method writes a message to the user log (ULOG) file. Messages are appended to the ULOG file with a tag made up of the time (hhmmss), system name, process name, and process-id of the invoking process. The tag is terminated with a colon.

We recommend that server applications limit their use of userlog() messages to messages that can be used to help debug application errors; flooding the ULOG file with incidental information can make it difficult to spot actual errors.

Return Value

The userlog() method returns the number of characters that were output, or a negative value if an output error was encountered. Output errors include the inability to open or write to the current log file.

Example

The following example shows how to use the TP::userlog() method:

userlog ("System exception caught: %s", e.get_id());

CosTransactions::TransactionalObject Interface Not Enforced

Use of this interface is now deprecated. Therefore, the use of this interface is now optional and no enforcement of descent from this interface is done for objects infected with transactions. The programmer can specify that an object is not to be infected by transactions by specifying the never or ignore transaction policies. There is no interface enforcement for eligibility for transactions. The only indicator is the transaction policy.

Error Conditions, Exceptions, and Error Messages

Exceptions Raised by the TP Framework

The following exceptions are raised by the TP Framework and are returned to clients when error conditions occur in, or are detected by, the TP Framework:

CORBA::INTERNAL
CORBA::OBJECT_NOT_EXIST
CORBA::OBJ_ADAPTER
CORBA::INVALID_TRANSACTION
CORBA::TRANSACTION_ROLLEDBACK

Since the reason for these exceptions may be ambiguous, each time one of these exceptions is raised, the TP Framework also writes a descriptive error message that explains the reason to the user log file.

Exceptions in the Server Application Code

Exceptions raised within a method invoked by a client are always raised back to the client exactly as they were raised in the method invoked by the client.

The following TP Framework callback methods are initiated by events other than client requests on the object:

Tobj_ServantBase::activate_object()
Tobj_ServantBase::deactivate_object()
Server::create_servant()

If exception conditions are raised in these methods, those exact exceptions are not reported back to the client. However, each of these methods is defined to raise an exception that includes a reason string. The TP Framework will catch the exception raised by the callback and log the reason string to the user log file. The TP Framework may raise an exception back to the client. Refer to the descriptions of the individual TP Framework callback methods for more information about these exceptions.

Example

For Tobj_ServantBase::deactivate_object(), the following line of code throws a DeactivateObjectFailed exception:

throw TobjS::DeactivateObjectFailed( "deactivate failed to save
                                       state!");

This message is appended to the user log file with a tag made up of the time (hhmmss), system name, process name, and process-id of the calling process. The tag is terminated with a colon. The preceding throw statement causes the following line to appear in the user log file:

151104.T1!simpapps.247: APPEXC: deactivate failed to save state!

Where 151104 is the time (3:11:04pm), T1 is the system name, simpapps is the process name, 247 is the process-id, and APPEXC identifies the message as an application exception message.

Exceptions and Transactions

Exceptions that are raised in either CORBA object methods or in TP Framework callback methods will not automatically cause a transaction to be rolled back unless the TP Framework started the transaction. It is up to the application code to call Current.rollback_only() if the condition that caused the exception to be raised should also cause the transaction to be rolled back.

Restriction of Nested Calls on CORBA Objects

The TP Framework restricts nested calls on CORBA objects. The restriction is as follows:

The TP Framework will detect the fact that a second CORBA object is acting as a client to an object that is already processing a method invocation, and will return a CORBA::OBJ_ADAPTER exception to the caller.

¹In theory, this would mean that an invocation on a transactional CORBA object in the same process would be valid since it would not require a new process to be registered with the transaction manager. However, it is not possible for the programmer to guarantee that an invocation on a CORBA object will occur in-proc, therefore, this practice is discouraged.