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, 25 insertions, 0 deletions

diff --git a/src/string.c b/src/string.c
new file mode 100644
index 0000000..878efeb
--- /dev/null
+++ b/src/string.c
@@ -0,0 +1,25 @@
+/*
+ * 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.
+ */
+
+#include "string.h"
+
+#include <string.h>
+
+char *stpecpy(char *dst, char *end, const char *src)
+{
+	if (!dst)
+		return NULL;
+	if (dst == end)
+		return end;
+
+	char *p = memccpy(dst, src, '\0', end - dst);
+	if (p)
+		return p - 1;
+
+	end[-1] = '\0';
+	return end;
+}