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QNX Software Development Platform
System Architecture
The System Architecture guide accompanies the QNX OS and is intended for both application developers and end-users.
The QNX OS Microkernel
The microkernel implements the core POSIX features used in embedded realtime systems, along with the fundamental QNX OS message-passing services.
Synchronization services
The QNX OS provides the POSIX-standard thread-level synchronization primitives, some of which are useful even between threads in different processes.

QNX Momentics IDE User's Guide
QNX Software Development Platform
- Quickstart Guide
- System Architecture
  The System Architecture guide accompanies the QNX OS and is intended for both application developers and end-users.
  - The Philosophy of the QNX OS
    The primary goal of the QNX OS is to deliver the open systems POSIX API in a robust, scalable form suitable for a wide range of systems—from tiny, resource-constrained embedded systems to high-end distributed computing environments. The OS supports several processor families, including x86 and ARM.
  - The QNX OS Microkernel
    The microkernel implements the core POSIX features used in embedded realtime systems, along with the fundamental QNX OS message-passing services.
    - Design goals of the QNX OS
      Historically, the application pressure on BlackBerry QNX's operating systems has been from both ends of the computing spectrum—from memory-limited embedded systems all the way up to high-end SMP (symmetrical multiprocessing) machines with gigabytes of physical memory.
    - System services
    - Threads and processes
      When building an application (realtime, embedded, graphical, or otherwise), the developer may want several algorithms within the application to execute concurrently. This concurrency is achieved by using the POSIX thread model, which defines a process as containing one or more threads of execution.
    - Thread scheduling
      When and how are scheduling decisions made?
    - Synchronization services
      The QNX OS provides the POSIX-standard thread-level synchronization primitives, some of which are useful even between threads in different processes.
      - Mutexes: mutual exclusion locks
        Mutual exclusion locks, or mutexes, are the simplest of the synchronization services. A mutex is used to ensure exclusive access to data shared between threads.
      - Condvars: condition variables
        A condition variable, or condvar, is used to block a thread within a critical section until some condition is satisfied. The condition can be arbitrarily complex and is independent of the condvar. However, the condvar must always be used with a mutex lock in order to implement a monitor.
      - Barriers
        A barrier is a synchronization mechanism that lets you corral several cooperating threads (e.g., in a matrix computation), forcing them to wait at a specific point until all have finished before any one thread can continue.
      - Sleepon locks
        Sleepon locks are very similar to condvars, with a few subtle differences.
      - Reader/writer locks
        More formally known as Multiple readers, single writer locks, these locks are used when the access pattern for a data structure consists of many threads reading the data, and (at most) one thread writing the data. These locks are more expensive than mutexes, but are useful for this data access pattern.
      - Safely sharing mutexes, barriers, and reader/writer locks between processes
        You can share most synchronization objects between processes, but security can be a concern.
      - Semaphores
        Semaphores are a common form of synchronization that allows threads to post and wait on a semaphore to control when threads wake or sleep.
      - Synchronization via message passing
        Our Send/Receive/Reply message-passing IPC services implement an implicit synchronization by their blocking nature. These IPC services can, in many instances, render other synchronization services unnecessary.
      - Synchronization via atomic operations
        In some cases, you may want to perform a short operation (such as incrementing a variable) with the guarantee that the operation will perform atomically—that is, the operation won't be preempted by another thread or parallel execution on different cores in SMP.
      - Synchronization services implementation
    - Clock and timer services
      Clock services are used to maintain the time of day, which is in turn used by the kernel timer calls to implement interval timers.
    - Interrupt handling
      No matter how much we wish it were so, computers are not infinitely fast. In a realtime system, it's absolutely crucial that CPU cycles aren't unnecessarily spent. But, it is important to balance this with safety, predictable behaviour, and an avoidance of run-time allocation or queueing. QNX OS implements a low-latency path to schedule user threads to handle hardware interrupts.
  - Interprocess Communication (IPC)
    Interprocess Communication (IPC) plays a fundamental role in the transformation of the microkernel from an embedded realtime kernel into a full-scale POSIX operating system. As various service-providing processes are added to the microkernel, IPC is the glue that connects those components into a cohesive whole.
  - The Microkernel Instrumentation
    The microkernel (procnto-smp-instr) is equipped with a sophisticated tracing and profiling mechanism that lets you monitor your system's execution in real time. This instrumentation works on both single-CPU and SMP systems.
  - Process Manager
    The process manager is capable of creating multiple POSIX processes (each of which may contain multiple POSIX threads).
  - Dynamic Linking
    In a typical system, a number of programs will be running. Each program relies on a number of functions, some of which will be standard C library functions, like printf(), malloc(), write(), etc.
  - Resource Managers
    To give the QNX OS a great degree of flexibility, to minimize the runtime memory requirements of the final system, and to cope with the wide variety of devices that may be found in a custom embedded system, the OS allows user-written processes to act as resource managers that can be started and stopped dynamically.
  - Filesystems
    The QNX OS provides a rich variety of filesystems. Like most service-providing processes in the OS, these filesystems execute outside the kernel; applications use them by communicating via messages generated by the shared-library implementation of the POSIX API.
  - Character I/O
    A key requirement of any realtime operating system is high-performance character I/O.
  - Networking Architecture
    As with other service-providing processes in the QNX OS, the networking services execute outside the kernel. Developers are presented with a single unified interface, regardless of the configuration and number of networks involved.
  - TCP/IP Networking
    Our TCP/IP stack is included in the io-sock networking stack and uses the common FreeBSD API.
  - High Availability
    The term High Availability (HA) is commonly used in telecommunications and other industries to describe a system's ability to remain up and running without interruption for extended periods of time.
  - What is Real Time and Why Do I Need It?
    Real time is an often misunderstood—and misapplied—property of operating systems. This appendix provides a summary of some of the critical elements of realtime computing and discusses a few design considerations and benefits.
  - Glossary
- OS Components
- Graphics
- Programming
- 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 OS applications and systems.
Typographical Conventions, Support, and Licensing
This section describes the typographical conventions used throughout the documentation and explains how to obtain technical support.

Synchronization services

QNX SDP8.0System ArchitectureDeveloperUser

The QNX OS provides the POSIX-standard thread-level synchronization primitives, some of which are useful even between threads in different processes.

The synchronization services include at least the following:


Synchronization service	Supported between processes
Mutexes	Yes^a
Condvars	Yes
Barriers	Yes^a
Sleepon locks	No
Reader/writer locks	Yes^a
Semaphores	Yes
Send/Receive/Reply	Yes
Atomic operations	Yes

^a Sharing this type of object between processes can be a security problem; see Safely sharing mutexes, barriers, and reader/writer locks between processes, later in this chapter.

The above synchronization primitives are implemented directly by the kernel, except for:

sleepon locks (which are built from mutexes and condvars)
atomic operations (which are implemented directly by the processor)

Note: You should allocate mutexes, condvars, barriers, reader/writer locks, and semaphores, as well as objects you plan to use atomic operations on, only in normal memory mappings. On certain processors, atomic operations and calls such as pthread_mutex_lock() will cause a fault if the object is allocated in uncached memory.

Page updated: May 17, 2024