Ulimit for LInux performance optimization

LInux performance tuning ulimit-General Linux technology-Linux technology and application information, the following is a detailed description. In Linux, a process can dynamically configure the number of threads and the size of the memory applied by the process. if so, when the actual number of threads or memory is large, if the ulimit limit is not enabled, then how does gcc handle it? can it be understood that the actual applied memory and number of threads in the process are false and not actually implemented, however, the program will not report an error. if so, it will become a logical task for the program to be unable to handle it. then how can we observe to confirm this problem? How can we make proper adjustments?