Home
QNX Software Development Platform
QNX SDP is a cross-compiling and debugging environment, including an IDE and command-line tools, for building binary images and programs for target boards running the QNX OS 8.0.
Programming
Programmer's Guide
The QNX OS Programmer's Guide covers a variety of topics that might interest developers who are building applications that will run under the QNX OS.
Working with Memory
(or The Persistence of Memory, with a nod to Salvador Dali) In the Process Manager chapter of the System Architecture guide, we looked at how the OS manages memory. This chapter describes how you can work with memory.
Memory objects
A memory object is a container for physical memory.

QNX Momentics IDE User's Guide
This User's Guide describes version 8.0 of the Integrated Development Environment (IDE) that's part of the QNX Tool Suite.
QNX Software Development Platform
QNX SDP is a cross-compiling and debugging environment, including an IDE and command-line tools, for building binary images and programs for target boards running the QNX OS 8.0.
- Quickstart Guide
- System Architecture
  The System Architecture guide accompanies the QNX OS and is intended for both application developers and end-users.
- OS Components & Operations
- Graphics
- Programming
  - Getting Started with the QNX OS
    Getting Started with the QNX OS: A Guide for Realtime Programmers is intended to introduce you to the QNX OS and help you develop applications and resource managers for it.
  - Programmer's Guide
    The QNX OS Programmer's Guide covers a variety of topics that might interest developers who are building applications that will run under the QNX OS.
    - Compiling and Debugging
      Let's start by looking at some things you should consider when you start to write a program for the QNX OS.
    - QNX OS Architecture and Concepts
      The QNX OS architecture consists of the microkernel and several cooperating processes. These processes communicate with each other via various forms of interprocess communication (IPC). Message passing is the primary form of IPC in QNX OS.
    - Processes
      Your applications should be written in a way that reflects the architecture of the QNX OS—as a set of cooperating processes. In this chapter, we see how to start processes (also known as creating processes) from code, how to terminate them, and how to detect their termination.
    - Multicore Processing
      Multiprocessing systems, whether discrete or multicore, can greatly improve your applications' performance.
    - Working with Access Control Lists (ACLs)
      Some filesystems, such as the Power-Safe (fs-qnx6.so) filesystem, extend file permissions with Access Control Lists, which are based on the withdrawn IEEE POSIX 1003.1e and 1003.2c draft standards.
    - Understanding the Microkernel's Concept of Time
      Whether you're working with timers or simply getting the time of day, it's important that you understand how the OS works with time.
    - Handling Hardware Interrupts
      This chapter explains the QNX OS mechanisms for quickly reacting to hardware events.
    - Working with Memory
      (or The Persistence of Memory, with a nod to Salvador Dali) In the Process Manager chapter of the System Architecture guide, we looked at how the OS manages memory. This chapter describes how you can work with memory.
      - Memory objects
        A memory object is a container for physical memory.
      - Memory management in QNX OS
        Let's consider memory management in general.
      - Dynamic memory management
        Let's examine how the heap is used for dynamically allocated memory.
      - Typed memory
        Your system's startup program can reserve memory pools to be used for special purposes, such as graphics. These pools are separate from SYSRAM.
      - Shared Memory
        Shared memory is an efficient way to share data among different processes.
      - Heap analysis
        If you develop a program that dynamically allocates memory, you're also responsible for tracking any memory that you allocate whenever a task is performed, and for releasing that memory when you no longer need it. If you fail to track the memory correctly, you may introduce memory leaks or unintentionally write to an area outside of the allocated memory space.
    - Freedom from Hardware and Platform Dependencies
      The QNX OS can run on many different hardware platforms. The way in which applications can access peripheral devices and how data is stored varies between platforms. This chapter explains our solutions for minimizing the impact of such platform dependencies.
    - Conventions for Recursive Makefiles and Directories
      In this chapter, we'll look at the supplementary files used in the QNX OS development environment. Although we use the standard make command to create libraries and executables, we also use some of our own conventions in the Makefile syntax.
    - Glossary
  - Writing a Resource Manager
- System Security Guide
  The QNX System Security Guide is intended for both system integrators who are responsible for the security of a QNX OS system and developers who want to create a QNX OS resource manager free from vulnerabilities.
- Utilities & Libraries
- Migrating to QNX OS 8.0
QNX Software in the Cloud
QNX Toolkit for Visual Studio Code
This User's Guide describes the QNX^® Toolkit for Visual Studio Code. The guide introduces you to the QNX Toolkit by explaining the QNX development environment and how to build, run, and debug your QNX^® Operating System (OS) applications and systems.
Typographical Conventions, Support, and Licensing
This section describes the typographical conventions used throughout the documentation, explains how to obtain technical support, and provides some information about licensing.

Memory objects

QNX SDP8.0Programmer's GuideDeveloper

A memory object is a container for physical memory.

We need to consider the following aspects:

Layout: The physical composition of the object: the physical memory pages that actually back the mapped memory. The pages might not yet exist; for example, if you've mapped a file, some of the pages might be in memory, and some might not have been loaded from the file. If you've allocated a contiguous object using shm_ctl(), the physical memory pages are in place. Nevertheless, all the pages form the layout of the object, and you can have more than one range of memory in an object.
Content: The data held by the object.

A memory object has a specific lifecycle; the object has a creator (or owner) and a reference count that the kernel maintains. The reference count increases as the object is created, duplicated, connected to, or mapped. It decreases when connections are severed, the object is unmapped, and so on. When the reference count goes to zero, the kernel destroys the object.

Here are some examples:

memory-mapped files
shared memory objects that you open with shm_open() and then expand with ftruncate()
contiguous memory allocated with mmap(MAP ANON | MAP PHYS). You don't see this object, and there's no way to change its layout, but the object is still there.
per-process anonymous memory

Note:

The direct mapping of physical addresses doesn't result in a memory object.

The main APIs for working with memory objects include the following:

shm_open(): Create a new shared memory object or open an existing one, based on a path under /dev/shmem.
posix_typed_mem_open(): Open a named memory pool that you can then allocate from.
shm_ctl(): A QNX OS function that lets you finely control the layout of an object that was opened with shm_open().
mmap(): Expose memory in the virtual address space.
ftruncate(): Expand or contract an object that was opened with shm_open(). This gives you pageable anonymous memory.

Page updated: August 09, 2024