This function registers a handler called name for signal number signal. The handler function is callback. The int argument of the callback is the signal number.

By default, the handler is an application handler. If library is set, the handler is for this library. The name passed as library is the findlib name of the library.

By registering another handler for the same library, name, and signal, the old handler is overridden.

When several handlers are defined for the same signal, all handlers are executed that are defined for the signal (when the signal happens). The order of execution is given by priority. The handler functions are executed in ascending priority order. If the priority number is equal for two handlers, the order is undefined.

The priority defaults to 0 for library handlers, and to 100 for application handlers. Libraries should only use values from 0 to 99, and applications only from 100 to 199.

If all handlers for a certain signal set keep_default, then there will be a special action after all signal handlers have been executed. The special action emulates the default behavior for the signal. For now, there is only a simple emulation: If the signal terminates the process, the process is immediately exited with code 126. If the default behaviour is "no-op", nothing happens. We don't try (yet) to do better (emulate core-dumps, emulate the right process status) because this is difficult in the general case.

The handler definition takes place immediately.

Any exceptions occuring during the execution of a handler are caught and ignored.

An exclusive handler for a signal is the only handler for the signal. If it is tried to register another handler when there is already an exclusive handler, the second registration fails. Also, an exclusive handler cannot be registered when there is already a normal handler for the signal. It is, however, possible to replace the registered exclusive handler by another exclusive handler for the same signal.

An exclusive handler is installed by running the install function, which can e.g. call Sys.set_signal to define the handler. Other methods (e.g. use some C wrapper) are also possible. It is assumed that install overrides any existing handler.

restore_management signo: Restores signal handling management for signo as defined by the handler list for this signal. Calling restore_management makes sense when the signal handler has been overridden with Sys.set_signal, but at some point this module is again responsible for managing the signal handling for this signal.

keep_away_from signo: This signal signo is added to the "keep away list". This means that this module will never try to change the signal behavior again for signo. Even restore_management will not restore the signal handling again. This function should only by called by applications wishing to do the signal handling all themselves.

This function does not have any effect on the already installed handlers. It is nevertheless useful for applications calling Sys.set_signal directly to ensure that Netsys_signal will never again try to override the handler.

Returns the list of signal handlers

Returns the "keep away list".

Call this function to ensure that this module is initialized. It is also possible to call any other function. After initialization the Sigpipe handler is set.