MEDIUM: signal: signal_unregister() removes every handlers

The new function signal_unregister() removes every handlers assigned to
a signal. Once the handler list of the signal is empty, the signal is
ignored with SIG_IGN.

include/proto/signal.h

@@ -32,6 +32,7 @@ struct sig_handler *signal_register_fct(int sig, void (*fct)(struct sig_handler
 struct sig_handler *signal_register_task(int sig, struct task *task, int reason);
 void signal_unregister_handler(struct sig_handler *handler);
 void signal_unregister_target(int sig, void *target);
+void signal_unregister(int sig);
 void haproxy_unblock_signals();
 
 static inline void signal_process_queue()

src/signal.c

@@ -254,3 +254,23 @@ void signal_unregister_target(int sig, void *target)
 		}
 	}
 }
+
+/*
+ * Immedialtely unregister every handler assigned to a signal <sig>.
+ * Once the handler list is empty, the signal is ignored with SIG_IGN.
+ */
+
+void signal_unregister(int sig)
+{
+	struct sig_handler *sh, *shb;
+
+	if (sig < 0 || sig >= MAX_SIGNAL)
+		return;
+
+	list_for_each_entry_safe(sh, shb, &signal_state[sig].handlers, list) {
+		LIST_DEL(&sh->list);
+		pool_free(pool_head_sig_handlers, sh);
+	}
+
+	signal(sig, SIG_IGN);
+}