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Extending Informix®
Beyond standard relational database objects, HCL Informix® can be extended to handle specialized data types, access methods, routines, and other objects. Informix includes many built-in extensions that are fully integrated in the database server. Informix also provides DataBlade® modules, which are packages of extended database objects for a particular purpose and that are installed separately from the database server. Alternatively, you can create your own user-defined objects for Informix.
Creating extensions
You can create user-defined data types, routines, access methods, and other database objects to suit your needs. You can use application programming interfaces to write user-defined routines and applications that access data in Informix® databases.
DataBlade® Developers Kit
The DataBlade® Developers Kit (DBDK) guides contain information about the tools you can use to develop and package DataBlade modules, which extend the functionality of HCL Informix® databases.
DataBlade® Developers Kit User's Guide
The HCL Informix® DataBlade® Developers Kit User's Guide describes how to use tools to develop and package DataBlade modules.
Programming guidelines
Use this section to help you when you write the design specification for your DataBlade® module.
C programming guidelines

Extending Informix®
Beyond standard relational database objects, HCL Informix® can be extended to handle specialized data types, access methods, routines, and other objects. Informix includes many built-in extensions that are fully integrated in the database server. Informix also provides DataBlade® modules, which are packages of extended database objects for a particular purpose and that are installed separately from the database server. Alternatively, you can create your own user-defined objects for Informix.
- Informix® extensions and DataBlade® modules
  These topics describe how to use built-in database extensions and separately installed DataBlade® modules.
- Creating extensions
  You can create user-defined data types, routines, access methods, and other database objects to suit your needs. You can use application programming interfaces to write user-defined routines and applications that access data in Informix® databases.
  - DataBlade® API Programmer's Guide
    The Informix® DataBlade® API Programmer's Guide describes information about the DataBlade API, the C-language application programming interface (API) provided with HCL Informix.
  - DataBlade® API Function Reference
    The Informix® DataBlade® API Function Reference describes the DataBlade API functions and the subset of Informix ESQL/C functions that the DataBlade API supports.
  - DataBlade® Developers Kit
    The DataBlade® Developers Kit (DBDK) guides contain information about the tools you can use to develop and package DataBlade modules, which extend the functionality of HCL Informix® databases.
    - DataBlade® Module Development Overview
      The HCL Informix® DataBlade® module overview serves as an overview of the HCL Informix DataBlade module development process.
    - DataBlade® Developers Kit User's Guide
      The HCL Informix® DataBlade® Developers Kit User's Guide describes how to use tools to develop and package DataBlade modules.
      - Getting started with DataBlade® module development
        This section provides an overview of DataBlade® module development and describes the resources and tools the HCL Informix® database server provides to facilitate development.
      - Design DataBlade® modules
        This section describes the DataBlade® module SQL design issues.
      - Programming guidelines
        Use this section to help you when you write the design specification for your DataBlade® module.
        Programming language options
        This section explains the programming language options you have when you use BladeSmith to generate source code for your DataBlade® module.
        C programming guidelines
        C++ programming guidelines
        Java™ programming guidelines
        DataBlade® API programming guidelines
      - Create DataBlade® objects by using BladeSmith
        Use BladeSmith to create DataBlade® modules.
      - Programming DataBlade® module routines in C
        This section contains information to help you edit and compile C language source code generated by DataBlade®.
      - Create ActiveX value objects
        This section describes how to use the to create ActiveX value objects. This section describes the use of C++ to implement opaque type support routines.
      - The ActiveX value objects
        This section provides information for client application developers who are using ActiveX value objects.
      - Programming DataBlade® modules in Java™
        This section contains information to help you edit and compile Java™ language source code generated by BladeSmith.
      - Debugging and testing DataBlade® modules on UNIX™
        This section describes how to debug and perform functional tests for DataBlade® modules written in C for Informix® on UNIX™.
      - Debugging and testing DataBlade® modules on Windows™
        This section describes how to debug and perform functional tests for DataBlade® modules written in C and C++ for Informix® on Windows™.
      - BladePack
        BladePack creates installation packages for DataBlade® modules and other software products.
      - Appendixes
        This section contains additional reference information.
    - DBDK InfoShelf
      The DataBlade® Developers Kit InfoShelf is designed to help you work with BladeSmith.
  - J/Foundation Developer's Guide
    The J/Foundation Developer's Guide describes how to write user-defined routines (UDRs) in the Java™ programming language for Informix®.
  - R-Tree Index User's Guide
    The Informix® R-Tree Index User's Guide describes the HCL Informix R-tree secondary access method and how to access and use its components.
  - User-Defined Routines and Data Types Developer's Guide
    The Informix® User-Defined Routines and Data Types Developer's Guide describes how to define new data types and enable user-defined routines (UDRs) to extend HCL Informix.
  - Virtual-Table Interface Guide
    The Informix® Virtual-Table Interface Programmer's Guide explains how to create a primary access method with the Virtual-Table Interface (VTI) so that users have a single SQL interface to HCL Informix tables and to data that does not conform to the storage scheme of HCL Informix.
  - Virtual-Index Interface Guide
    The Informix® Virtual-Index Interface Programmer's Guide explains how to create a secondary access method with the Virtual-Index Interface (VII) to extend the built-in indexing schemes of HCL Informix typically with a DataBlade® module.

C programming guidelines

To take advantage of HCL Informix® database server architecture, you must use the DataBlade® API and follow the guidelines in the Informix® DataBlade® API Programmer's Guide when you write user-defined routines in C.

The Informix® database server uses virtual processors (VPs) to service multiple client-application SQL requests. The database server breaks the SQL request into distinct tasks, based on the resource that the task requires. Different VP types, called virtual processor classes (VP classes), service different kinds of tasks.

The CPU virtual processor (CPU VP) acts as the central processor for client-application SQL requests. When a client application establishes a connection, the CPU VP creates the session thread for that client application. A CPU VP runs multiple session threads to service multiple SQL client applications. Because a session thread is the primary thread for the processing of SQL requests, any C routines in an SQL request normally execute in the CPU VP. However, your routine must be well-behaved by following certain guidelines to avoid loss of performance and data.

For example, a well-behaved user-defined routine that runs in the CPU VP must fulfill the following requirements:

Preserve concurrency by following these rules:
- Yield the CPU VP regularly by using the mi_yield() DataBlade® API function.
- Do not use blocking I/O calls.
Be thread safe by following these rules:
- Do not use heap-memory allocation; instead use the DataBlade® API memory-management functions.
- Do not modify global or static data; instead use the MI_FPARAM structure to preserve state information.
- Do not modify the global state of the CPU VP.
Do not use unsafe operating system calls that might impair concurrency or allocate local resources.

Some of these restrictions are relaxed if you assign your routine to a user-defined virtual processor. A user-defined virtual processor is a VP that you create. It runs only those routines that you assign to it.

The Informix® DataBlade® API Programmer's Guide describes in detail each of these guidelines and their possible workarounds with user-defined virtual processors.