Multithreading in Embedded Systems

Question

I am confused about the following:

I am hoping to get a job in the field of embedded systems. However, every interview I've had seems to end up with a conversation about threads in C and how to do thread-safe programming

My question is how do I go about learning multithreading in embedded systems? Are they the same as POSIX threads? For example, the tasks in FreeRTOS. Are they same thing as pthreads?

Can someone give me some tips on what to do and where to start?

Most embedded systems are either no OS at all or RTOS. Meaning that threads are rare. However, the concepts of re-entrancy and race conditions are important to understand no matter, because these do not only exist in threads, but also when writing interrupts, dual core or multi-process programs. Basically someone who is writing a low-level microcontroller program where an interrupt disrupts the main program when new data comes in, is facing the very same issues as someone writing a high-level, multi-threaded Windows program where one thread gives input to the program. — Lundin, Jun 20 '17 at 06:48

score 3 · Answer 1 · answered Jun 20 '17 at 05:28

Every OS has it's own threads/task/processes characteristics. Despite the differences, the methods to synchronize, guard and interchange data between those, are roughly the same.

If someone knows that you don't know a specific OS, invited you to an interview - he/she probably expects you to answer in general and not to be OS specific. You can solve any problem with POSIX (or any other) tool-set in mind and to mention that migration of the solution to a non-POSIX environment will keep same logic with some minor adaptations.

score 0 · Answer 2 · answered Jun 20 '17 at 08:03

Multithreading concept is almost same everywhere, whether in RTOS or Linux. The difference is in the operational behavior.

My question is how do I go about learning multithreading in embedded systems?

My suggestion is to first learn and understand the concepts of multithreading by referring some online material, you can practice by writing some simple codes on your desktop running any flavor of Linux.

The go for some advanced topics like synchronization mechanism using Semaphore and Mutexes, you will then get to learn about the basic concept of when to use a semaphore and when to use a mutex for thread synchronization.

Then move to some Embedded Targets and try out some code using uCOS-II/uCOS-III or FreeRTOS.

Are they the same as POSIX threads?

No, they are not exactly same, POSIX thread library is a bit advance and is highly portable on different OS. For e.g. a multithread code written on Linux using pthread can also be compiled and executed on Windows with little or no change.

On the other hand, a thread implementation on RTOS is different, threads in RTOS are treated as tasks and they start executing only when a call to start the scheduler is made.

Thanks for your answer. Are there any other mechanisms I need to learn other than Mutexes and Semaphores? — Ali Kurabiyeci, Jun 20 '17 at 11:46
Yes, you also need to understand intertask/interprocess communication in Linux and RTOS as well. — Gaurav Pathak, Jun 21 '17 at 08:44

score 0 · Answer 3 · answered Mar 19 '20 at 18:20

From my own experience trying to find learning resources, I found the the FreeRTOS docs very useful. They have both a reference manual as well as the Mastering the FreeRTOS Kernal doc which includes code snippets and covers topics such as task management, software timers, resource management, and general thread safe programming techniques. I dont think this would be the best place to start out, but once you've familiarized yourself with basics the other answers and comments have mentioned, this could help with the next step of learning by doing.

Multithreading in Embedded Systems

3 Answers3