Change sigprocmask in multi-threaded processes to pthread_sigmask to avoid undefined behaviour

"Note that you must not use sigprocmask in multi-threaded processes, because each thread has its own signal mask and there is no single process signal mask. According to POSIX, the behavior of sigprocmask in a multi-threaded process is “unspecified”. Instead, use pthread_sigmask."
https://www.gnu.org/software/libc/manual/html_node/Process-Signal-Mask.html

Currently server cannot be stopped on Mac OS, manager no longer receives signal due to usage of sigprocmask in startup logs.