setjmp() and longjmp() are useful for dealing with errors and
interrupts encountered in a low-level subroutine of a program. setjmp()
saves the stack context/environment in env for later use by
longjmp(). The stack context will be invalidated if the function which
called setjmp() returns.
sigsetjmp() is similar to setjmp(). If savesigs is nonzero,
the set of blocked signals is saved in env and will be restored if a
siglongjmp() is later performed with this env.
POSIX does not specify whether setjmp will save the signal context. (In
SYSV it will not. In BSD4.3 it will, and there is a function _setjmp
that will not.) If you want to save signal masks, use sigsetjmp.
setjmp() and sigsetjmp make programs hard to understand and
maintain. If possible an alternative should be used.