Add malloc_count Component to track heap usage

[mikee47]

Currently, system_get_free_heap_size() doesn't return anything meaningful. This PR fixes that using a Component based on malloc_count https://panthema.net/2013/malloc_count/.

I've also added a couple of functions to enable logging. To use it, add #include <malloc_count.h> and call MallocCount::enableLogging() and MallocCount::setLogThreshold() as required.

The Component also works for the Esp8266 (standard or custom heaps). Enable by adding COMPONENT_DEPENDS += malloc_count to the project's component.mk file.

The Component is enabled by default for the Host emulator, but can be disabled using ENABLE_MALLOC_COUNT=0.

[mikee47]

It would probably be useful to add an option to disable this if using valgrind, ENABLE_MALLOC_COUNT,
but I think should be enabled by default.

As the API is only available for Host builds it needs to be conditionally compiled (using #ifdef ARCH_HOST). An alternative is to make this a generic Component so it can be used on any architecture, with a common API. However, the ESP32 (and Esp8266 RTOS) use Espressif's 'capability heap' and includes tracing support. As a separate issue then, perhaps we should take a look at that and see if it offers any improvements over the existing heap allocation options?

[slaff]

It would probably be useful to add an option to disable this if using valgrind, ENABLE_MALLOC_COUNT,

Yes, please.

[slaff]

The Windows build is failing. That is probably due to the concurrency and the way windows handles files. I saw "Error 5" in the error output which lead me to this post: https://stackoverflow.com/questions/14201870/cmake-fails-to-compile-simple-test-error-5-access-denied.

[mikee47]

I've logged in via RDP to find out what's going on here. There's some mingw startup code which calls free on memory which wasn't allocated via malloc_count, which leads to a sentinel check failure. The code then goes on to call __real_free() on an invalid location (ptr - 16) hence access denied. I'll do some more testing and fix this.

[slaff]

@mikee47 Is this PR ready for merging?

[mikee47]

@slaff Yep, all done thanks.