ESP32 Forum

Hi there!

Could anyone clarify for me please whether malloc/new are thread and interrupt safe? I can see that there is an implementation of _malloc_r in newlib directory which is considered to be thread safe. But what about common malloc? Regarding to the documentation it seems that malloc and _malloc_r wrap the same functions, however, I can not confirm that since I can not find malloc implementation anywhere. And what about new operator? Is it a simple wrapper about malloc as it used to be? Also I am not sure whether it is safe to call malloc/new inside an ISR.

Actually I do not like the idea of calling malloc inside interrupt handler, therefore I would like to write my own block memory allocator for allocating objects in ISR, however, I am not sure how to make it safe if interrupts are nested. Is portENTER_CRITICAL_ISR enough to prevent nesting?

They are threadsafe, but I would not assume they are interrupt-safe. I'm not sure why you would do a malloc in an ISR anyway, and even if it worked it does not sound like a good idea;l what's your use case there?

ESP_Sprite wrote: ↑

Wed Dec 12, 2018 3:18 am

They are threadsafe, but I would not assume they are interrupt-safe. I'm not sure why you would do a malloc in an ISR anyway, and even if it worked it does not sound like a good idea;l what's your use case there?

Thanks for your reply! I allocate small event structures in order to avoid having huge tables or filling any table by means of c++ functionality. I do not like that idea too and as I said in original post I would like to switch to custom block allocator which will be very fast. However I am not sure how to prevent interrupt nesting.

Why not use an existing structure, like a FreeRTOS queue?