Returns an estimation of virtual address space remaining in this process if chunks are allocated in size chunk. How this is implemented is highly system specific and for some systems is quite hackish so the value can vary by +-5% depending on what thread is calling it and such. At least two allocations of size chunk will need to be temporarily made and the returned value assumes that there are no other allocations between that chunk and the end of address space which clearly can be wildly out. On all supported platforms actual increases in the memory usage of your process can be avoided. You probably want to avoid calling this too frequently as it involves multiple calls into kernel space.
