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-sigchain API
-============
-
-Code often wants to set a signal handler to clean up temporary files or
-other work-in-progress when we die unexpectedly. For multiple pieces of
-code to do this without conflicting, each piece of code must remember
-the old value of the handler and restore it either when:
-
- 1. The work-in-progress is finished, and the handler is no longer
- necessary. The handler should revert to the original behavior
- (either another handler, SIG_DFL, or SIG_IGN).
-
- 2. The signal is received. We should then do our cleanup, then chain
- to the next handler (or die if it is SIG_DFL).
-
-Sigchain is a tiny library for keeping a stack of handlers. Your handler
-and installation code should look something like:
-
-------------------------------------------
- void clean_foo_on_signal(int sig)
- {
- clean_foo();
- sigchain_pop(sig);
- raise(sig);
- }
-
- void other_func()
- {
- sigchain_push_common(clean_foo_on_signal);
- mess_up_foo();
- clean_foo();
- }
-------------------------------------------
-
-Handlers are given the typedef of sigchain_fun. This is the same type
-that is given to signal() or sigaction(). It is perfectly reasonable to
-push SIG_DFL or SIG_IGN onto the stack.
-
-You can sigchain_push and sigchain_pop individual signals. For
-convenience, sigchain_push_common will push the handler onto the stack
-for many common signals.