How to call LwIP thread-unsafe functions when using FreeRTOS?

[_AdamNtrx]

Hello!

I am writing a program that uses FreeRTOS and LwIP libraries. I would want to check ARP table, but functions from ip4 directory are not considered thread-safe. How can I check ARP table when using FreeRTOS or how can I make sure calling thread-unsafe functions won't break my program?

I saw that there is an LwIP mutex that can be used to lock the stack via LOCK_TCPIP_CORE() and UNLOCK_TCPIP_CORE() macros, but I am not sure how to use them properly or if it is even a good approach.

Thank you in advance!

[MOBEJ]

Hello @_AdamNtrx ?

Could you please confirm which STM32 board you are using  for your project? This will help us provide you with the accurate example of LWIP using FreeRTOS.

Br

[TDK]

Use a mutex to ensure only one thread is calling a function at once. Or, only call LwIP functions from a single thread.

[_AdamNtrx]

I use STM32F769I-DISCOVERY board.

[_AdamNtrx]

Does that mean as long as unsafe LwIP functions are not called simultaneously they are fine to use?

[Ozone]

Yes and no.

As long as you keep your LwIP calls to one thread / task, you are safe.
In a preemptive multitasking system, any calls to the same function from different tasks will eventually be "simultaneous", statistically speaking.

[_AdamNtrx]

Alright, so if LwIP functions are either called only in one task or are protected by mutex, they are fine. Got it.

What about (UN)LOCK_TCPIP_CORE() macros? How to use them? Or should they be used at all?

[MOBEJ]

Hello @_AdamNtrx , 

Please check out the lwIP projects on GitHub for the STM32F769I board. It can help you with your issue

BR