Stack blowed

[ComputerProgrammerStorager]

In thread subroutine run_service, it uses stack space as the buffer (see line 453 and 465). Given the default number of service thread being 5 times of the cpu cores on the host and the read_size seeming to be a random value, how likely is it to exhaust the stack space so that actually few numbers of threads would be created (and few I/O would be executed than specified, resulting in a superficially higher score) ? Using thread stack this way could be dangerous. Could we change it to use heap memory as the buffer?