The signal-chaining facility was introduced in JDK 1.4 and supported three different Linux signal-handling API's: `sigset`, `signal` and `sigaction`. Only `sigaction` is a cross-platform, supported, API for multi-threaded processes. Both `signal` and `sigset` are considered obsolete on those platforms that still define them. Consequently, the use of `signal` and `sigset` with the signal-chaining facility are now deprecated, and support for their use will be removed in a future release.