use signalfd to stop on SIGTERM

Is this an overkill? I don't know.

The thing is, correctly intercepting SIGTERM (also SIGINT, etc.) is
incredibly tricky. For example, before this commit, my I/O loops in
server.c and worker.c were inherently racy.

This was immediately obvious if you tried to run the tests. The tests
(especially the Valgrind flavour) would run a worker, wait until it
prints a "Waiting for a new command" line, and try to kill it using
SIGTERM. The problem is, the global_stop_flag check could have already
been executed by the worker, and it would hang forever in recv().

The solution seems to be to use signalfd and select()/poll(). I've never
used either before, but it seems to work well enough - at least the very
same tests pass and don't hang now.

1 files changed, 3 insertions, 0 deletions

diff --git a/src/command.h b/src/command.h
index 90facbb..3d13abd 100644
--- a/src/command.h
+++ b/src/command.h
@@ -8,6 +8,7 @@
 #ifndef __COMMAND_H__
 #define __COMMAND_H__
 
+#include "event_loop.h"
 #include "msg.h"
 
 #include <stddef.h>
@@ -28,6 +29,8 @@ void cmd_dispatcher_destroy(struct cmd_dispatcher *);
 int cmd_dispatcher_handle(const struct cmd_dispatcher *, const struct msg *command,
                           struct msg **response);
 
+int cmd_dispatcher_add_to_event_loop(const struct cmd_dispatcher *, struct event_loop *, int fd);
+
 struct cmd_conn_ctx {
 	int fd;
 	void *arg;