SIG30-C. Call only asynchronous-safe functions within signal handlers

Call only asynchronous-safe functions within signal handlers. For strictly conforming programs, only the C standard library functions abort() , _Exit() , quick_exit() , and signal() can be safely called from within a signal handler.

The C Standard, 7.14.1.1, paragraph 5 [ ISO/IEC 9899:2024 ], states that if the signal occurs other than as the result of calling the abort() or raise() function, the behavior is undefined if

If the signal occurs other than as the result of calling the abort or raise function, the behavior is undefined if the signal handler refers to any object with static or thread storage duration that is not a lock-free atomic object and that is not declared with the constexpr storage-class specifier other than by assigning a value to an object declared as volatile sig _ atomic _ t , or the signal handler calls any function in the standard library other than

—  the abort function,

—  the _ Exit function,

—  the quick _ exit function,

—  the functions in <stdatomic.h> (except where explicitly stated otherwise) when the atomic arguments are lock-free,

—  the atomic _ is _ lock _ free function with any atomic argument, or

—  the signal function with the first argument equal to the signal number corresponding to the signal that caused the invocation of the handler. Furthermore, if such a call to the signal function results in a SIG _ ERR return, the object designated by errno has an i