12 Using Cartridge Services

Introduction to Cartridge Services

This chapter describes a set of services that help you create data cartridges in the Oracle Extensibility framework.

Using Oracle Cartridge Services offers you the following advantages:

Portability

Oracle Cartridge Services offers you the flexibility to work across different machine architectures

Flexibility Within Oracle Environments

Another type of flexibility is offered to you in terms of the fact that all cartridge services work with your Oracle Database, irrespective of the configuration of operations that has been purchased by your client.

Language Independence

The use of the Globalization Support services lets you internationalize your cartridge. Language independence means that you can have different instances of your cartridge operating in different language environments.

Tight Integration with the Server

Various cartridge services have been designed to facilitate access with Oracle ORDBMS. This offers far superior performance to client -side programs attempting to perform the same operations.

Guaranteed Compatibility

Oracle Database is a rapidly evolving technology and it is likely that your clients might be operating with different releases of Oracle. The cartridge services operate with all versions of Oracle Database.

Integration of Different Cartridges

The integration of cartridge services lets you produce a uniform integration of different data cartridges.

The following sections provide a brief introduction to the set of services that you can use as part of your data cartridge. The APIs that describe these interfaces are in Chapter 18, "Cartridge Services Using C, C++ and Java"

Cartridge Handle

Cartridge services require various handles that are encapsulated inside two types of OCI handles:

Environment Handle

The environment handle is either OCIEnv or OCI_HTYPE_ENV. Various cartridge services are required at the process level when no session is available. The OCIInitialize() should use the OCI_OBJECT option for cartridge service.

User Session handle

The user session handle is either OCISession or OCI_HTYPE_SESSION. In a callout, the services can be used when the handle is allocated even without opening a connection back to the database.

All cartridge service calls take a void * OCI handle as one of the arguments that may be either an environment or a session handle. While most service calls are allowed with either of the handles, certain calls may not be valid with one of the handles. For example, it may be an error to allocate OCI_DURATION_SESSION with an environment handle. An error is typically returned in an error handle.

{
  OCIEnv *envhp;
  OCIError *errhp;
  (void) OCIInitialize(OCI_OBJECT, (dvoid *)0, 0, 0, 0);
  (void) OCIEnvInit(&envhp, OCI_OBJECT, (size_t)0, (dvoid **)0);
  (void) OCIHandleAlloc((dvoid *)envhp, (dvoid **)errhp,   OCI_HTYPE_ERROR, 
      (size_t)0, (dvoid **)0);
  /* ... use the handles ... */
  (void) OCIHandleFree((dvoid *)errhp, OCI_HTYPE_ERROR);
}

{
  OCIError *errhp;
  ub4 errcode;
  text buffer[512];
  (void) OCIErrorGet((dvoid *)errhp, 1, (text *)NULL, &errcode, buffer,
      sizeof(buffer), OCI_HTYPE_ERROR);
}

Memory Services

The memory service allows the client to allocate or free memory chunks. Each memory chunk is associated with a duration. This allows clients to automatically free all memory associated with a duration (at the end of the duration). The duration determines the heap that is used to allocate the memory. The memory service predefines three kinds of durations: call (OCI_DURATION_CALL), statement (OCI_DURATION_STATEMENT) and session (OCI_DURATION_SESSION).

The client can also create a user duration. The client has to explicitly start and terminate a user duration. Thus, the client can control the length of a user duration. Like the predefined durations, a user duration can be used to specify the allocation duration (for example, memory chunks are freed at the end of the user duration).

Each user duration has a parent duration. A user duration terminates implicitly when its parent duration terminates. A parent duration can be call, statement, transaction, session or any other user duration. Memory allocated in the user duration comes from the heap of its parent duration.

The Oracle RDBMS memory manager supports a variety of memory models. Currently callouts support memory for the duration of that callout. With the extension of row sources to support external indexing, there is a need for memory of durations greater than a callout.

The following functionality is supported:

• Allocate (permanent and friable) memory of following durations

  • call to agent process

  • statement

  • session

  • shared attributes (metadata) for cartridges

• Ability to re-allocate memory

• Ability to create a subduration memory, a sub heap which gets freed up when the parent heap gets freed up. Memory for this sub heap can be allocated and freed.

• Ability to specify zeroed memory

• Ability to allocate large contiguous memory

Maintaining Context

Context management allows the clients to store values across calls. Cartridge services provide a mechanism for saving and restoring context.

Most operating systems that support threads have the concept of thread context. Threads can store thread specific data in this context (or state) and retrieve it at any point. This provides a notion of thread global variable. Typically a pointer which points to the root of a structure is stored in the context.

When the row source mechanism is externalized, you must have a mechanism to maintain state between multiple calls to the same row source.

You must maintain session, statement and process states. Session state includes information about multiple statements that are open, message files based on sessions' Globalization Support settings, and so on. Process state includes shared metadata (including systemwide metadata), message files, and so on. Depending on whether the cartridge application is truly multi threaded, information sharing can be at a process level or system level.

Since a user can be using multiple cartridges at any time, the state must be maintained for each cartridge. This is done by requiring the user to supply a key for each duration.

Globalization Support

To support multilingual application, Globalization Support functionality is required for cartridges and callouts. NLSRTL is a multiplatform, multilingual library current used in RDBMS and provides consistent Globalization Support behavior to all Oracle products.

Globalization Support basic services provide the following language and cultural sensitive functionality:

• Locale information retrieval.

• String manipulation in the format of multibyte and wide-char.

• Character set conversion including Unicode support.

• Messaging mechanism.

Parameter Manager Interface

The parameter manager provides a set of routines to process parameters from a file or a string. Routines are provided to process the input and to obtain key and value pairs. These key and value pairs are stored in memory and routines are provided which can access the values of the stored parameters.

The input processing routines match the contents of the file or the string against an existing grammar and compare the key names found in the input against the list of known keys that the user has registered. The behavior of the input processing routines can be configured depending on the bits that are set in the flag argument.

The parameters can be retrieved either one at a time, or all at the same time by calling a function that iterates over the stored parameters.

File I/O

The OCI file I/O package is designed to make it easier for you to write portable code that interacts with the file system by providing a consistent view of file I/O across multiple platforms.

You must be aware of two issues when using this package in a data cartridge environment. The first issue is that this package does not provide any security when opening files for writing or when creating new files in a directory other than the security provided by the operating system protections on the file and directory. The second issue is that this package does not support the use of file descriptors across calls in a multithreaded server environment.

String Formatting

The OCI string formatting package facilitates writing portable code that handles string manipulation by means of the OCIFormatString() routine. This is an improved and portable version of sprintf that incorporates additional functionality and error checking that the standard sprintf does not. This additional functionality includes:

• Arbitrary argument selection.

• Variable width and precision specification.

• Length checking of the buffer.

• Oracle Globalization Support for internationalization.