Real-Time Considerations and Latency
Write code with predictable timing for soft and hard real-time systems.
Real-Time Considerations and Latency is a free C++ Academy lesson on CoddyKit — lesson 3 of 4. You can read the complete lesson below for free — then practise it hands-on in the browser with a built-in code editor and a 24/7 AI tutor. It is part of the C++ Academy learning path, one of 4 lessons in the course, and your progress syncs across the web and the CoddyKit app.
What is Real-Time?
A real-time system must respond within a deadline. Missing deadlines causes failure:
- Hard real-time — missed deadline is a system failure (medical, avionics)
- Soft real-time — missed deadlines degrade quality but are tolerated (audio, video)
Determinism Beats Speed
Real-time code values predictable timing over peak performance. A function that always takes 10us is preferred over one that takes 1-20us.
Avoid Heap Allocation
Heap operations are unpredictable — fragmentation, allocator decisions. Allocate at startup and reuse. Embedded coding standards often forbid new outside init.
Avoid Exceptions
Exception throwing has unpredictable cost. Most real-time C++ code compiles with -fno-exceptions.
Avoid Virtual Calls in Hot Paths
Virtual functions add an indirection and can pollute branch prediction. Use templates or CRTP for static polymorphism.
Lock-Free for Determinism
Locks can cause priority inversion — a low-priority thread holding a lock blocks a high-priority one. Lock-free data structures avoid the issue.
Priority Inversion Mitigation
If you must use locks, prefer those that support priority inheritance — the OS raises the locker s priority temporarily.
Worst-Case Execution Time (WCET)
Analyze the worst path through your code. Tools and manual analysis estimate the maximum cycles a function can take. WCET drives scheduling decisions.
Avoid the OS Scheduler
For hard real-time, use an RTOS (FreeRTOS, Zephyr, VxWorks) or bare-metal. General-purpose OSes can delay your task indefinitely.
Cache and TLB Effects
Cache misses and TLB misses cause unpredictable stalls. Lock data into the cache or use scratchpad RAM for the most critical sections.
Memory Pools
Allocate from pre-sized pools instead of the general heap. Constant-time alloc/free. Many embedded C++ projects rely on them exclusively.
Profile on the Real Hardware
Performance on a workstation has little to do with performance on an MCU. Always benchmark on the target hardware with realistic load.
Quick Check
Why are heap allocations problematic in real-time C++ code?
Recap
Real-time C++ favors predictability over peak performance. Avoid heap, exceptions, virtual calls, and OS-managed locks. Use static memory, memory pools, lock-free structures, and analyze worst-case execution time. Profile on the actual target.
Frequently asked questions
Is the “Real-Time Considerations and Latency” lesson free?
Yes — the full text of “Real-Time Considerations and Latency” is free to read here on the web, and the C++ Academy course includes 4 lessons in total. To practise it interactively (a built-in code editor and a 24/7 AI tutor) and unlock the rest of the C++ Academy course, upgrade to CoddyKit PRO.
What will I learn in “Real-Time Considerations and Latency”?
Write code with predictable timing for soft and hard real-time systems. You practise C++ Academy with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.
Do I need any experience to start C++ Academy?
No prior experience is required. C++ Academy on CoddyKit is structured for beginners through advanced learners; this is — lesson 3 of 4, so you can start here or from the beginning and move at your own pace.
How long does the “Real-Time Considerations and Latency” lesson take?
Most CoddyKit lessons take about 5–10 minutes. Each one is bite-sized and interactive, so you make steady progress and pick up exactly where you left off across the web and the app.
Can I write and run code in this C++ Academy lesson?
Yes. Every C++ Academy lesson includes a built-in code editor, so you write and run real code right in your browser and get instant AI feedback — no local setup required.
All lessons in this course
- Constraints in Embedded No RTTI No Exceptions
- Memory Mapped IO and Volatile
- Real-Time Considerations and Latency
- Cross-Compilation for ARM Targets