sigsetmask

The `sigsetmask` function is a POSIX-compliant system call used in Unix-like operating systems to manipulate the signal mask of the calling process. It allows a program to temporarily block or unblock specific signals, controlling which signals can interrupt the process while it executes certain critical sections of code.

The function takes a single argument, `sigmask`, which is a bitmask representing the set of signals to be added to the current signal mask. Each bit in the mask corresponds to a specific signal number, where a set bit indicates that the signal should be blocked. The signal mask determines which signals are pending but not yet delivered to the process, preventing them from interrupting execution until unblocked.

Prior to the introduction of `sigprocmask` in POSIX.1-2008, `sigsetmask` was the primary method for managing signal masks. However, it has been largely superseded by more flexible alternatives like `sigprocmask` and `pthread_sigmask` due to its limited functionality and lack of support for fine-grained control over signal handling. `sigsetmask` remains available for backward compatibility but is generally discouraged in new code.

The function returns 0 on success, or -1 on failure, with `errno` set to indicate the error (e.g., `EINVAL` if an invalid signal number is provided). While `sigsetmask` is simple, its use is not recommended for new applications, as it does not support asynchronous signal safety or the more granular control provided by modern alternatives. Developers should prefer `sigprocmask` for managing signal masks in modern systems.