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, 36 insertions, 0 deletions

diff --git a/src/event_loop.h b/src/event_loop.h
new file mode 100644
index 0000000..eb5ff05
--- /dev/null
+++ b/src/event_loop.h
@@ -0,0 +1,36 @@
+/*
+ * Copyright (c) 2023 Egor Tensin <Egor.Tensin@gmail.com>
+ * This file is part of the "cimple" project.
+ * For details, see https://github.com/egor-tensin/cimple.
+ * Distributed under the MIT License.
+ */
+
+#ifndef __EVENT_LOOP_H__
+#define __EVENT_LOOP_H__
+
+#include <poll.h>
+#include <sys/queue.h>
+
+struct event_loop;
+
+int event_loop_create(struct event_loop **);
+void event_loop_destroy(struct event_loop *);
+
+int event_loop_run(struct event_loop *);
+
+#define EVENT_LOOP_REMOVE 1
+
+typedef int (*event_loop_handler)(struct event_loop *, int fd, short revents, void *arg);
+
+struct event_fd {
+	int fd;
+	short events;
+	event_loop_handler handler;
+	void *arg;
+
+	SIMPLEQ_ENTRY(event_fd) entries;
+};
+
+int event_loop_add(struct event_loop *, const struct event_fd *);
+
+#endif