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-rw-r--r--sigchain.h45
1 files changed, 45 insertions, 0 deletions
diff --git a/sigchain.h b/sigchain.h
index 138b20f54b..8e6bada892 100644
--- a/sigchain.h
+++ b/sigchain.h
@@ -1,12 +1,57 @@
#ifndef SIGCHAIN_H
#define SIGCHAIN_H
+/**
+ * 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.
+ */
typedef void (*sigchain_fun)(int);
+/* You can sigchain_push and sigchain_pop individual signals. */
int sigchain_push(int sig, sigchain_fun f);
int sigchain_pop(int sig);
+/**
+ * push the handler onto the stack for the common signals:
+ * SIGINT, SIGHUP, SIGTERM, SIGQUIT and SIGPIPE.
+ */
void sigchain_push_common(sigchain_fun f);
+
void sigchain_pop_common(void);
#endif /* SIGCHAIN_H */