Hi I wanna ask about heap3? I didn't know how it's thread safe when i used it it's the only heap that made my used RAM lower why and how?

This might help: http://www.freertos.org/a00111.html

wanna

Please use correct spellings in consideration of readers for whom English is a second language.

I didn't know how it's thread safe when i used it it's the only heap that made my used RAM lower why and how?

If you are using heap3 then malloc() is provided by your compiler, so we can't answer this and you will need to refer to the compiler documentation or vendor support. However, heap3 uses crude scheduler locks to ensure calls to malloc() and free cannot be interrupted by other tasks.