[SOLVED] How to reuse Stack Allocator in RapidJSON without reallocating memory

How to reuse Stack Allocator in RapidJSON without reallocating memory

I'm running a single-threaded system in FreeRTOS with limited resources.

I already preallocate buffers for the RapidJSON allocators as so:

char            valueBuffer[2048];
char            parseBuffer[1024];
rapidjson::MemoryPoolAllocator<FreeRTOSRapidJSONAllocator> valueAllocator (valueBuffer, sizeof(valueBuffer))
rapidjson::MemoryPoolAllocator<FreeRTOSRapidJSONAllocator> parseAllocator (parseBuffer, sizeof(parseBuffer));

The issue I have is that every time one of the allocators is used, its size keeps on increasing (and allocating new memory if necessary) unless they are cleared. The problem with calling Clear() on the allocators is that Malloc is called again when the allocators are next resized, which I want to avoid.

Is there a way to simply reuse the existing preallocated memory, such as by setting the allocators' size back to zero, for example?

Solution

I resolved this by creating a custom allocator. Essentially a copy of rapidjson::MemoryPoolAllocator with the addition of the following method:

void Reset()
{
    chunkHead_->size = 0;
    chunkHead_->next = 0;
}

Which should be called every time you're done with the last string that was parsed.