cron: New API for absolute timers

This patch adds support for at/cron-like jobs that need an absolute
timer.  The API supports waking up with an UEV_HUP callback event if the
wall clock changed due to NTP or user input while waiting.

- uev_cron_init()
- uev_cron_set()
- uev_cron_start()
- uev_cron_stop()

A very simple cronrun example/test program is also included.

Signed-off-by: Joachim Nilsson <troglobit@gmail.com>

examples/.gitignore

@@ -0,0 +1,4 @@
+joystick
+signal
+cronrun
+test

examples/Makefile.am

@@ -1,4 +1,4 @@
-noinst_PROGRAMS = signal test joystick
+noinst_PROGRAMS = signal test joystick cronrun
 AM_CPPFLAGS     = -I$(top_srcdir)
 AM_LDFLAGS      = -L$(top_srcdir)
 LIBS            = $(LTLIBINTL)

examples/cronrun.c

@@ -0,0 +1,68 @@
+/* Test cron API in libuEv event library
+ *
+ * Copyright (c) 2016  Joachim Nilsson <troglobit()gmail!com>
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+#include <stdio.h>
+#include <time.h>
+#include <sys/time.h>
+#include "uev.h"
+
+#define UNUSED(arg) arg __attribute__ ((unused))
+
+
+static void cron_job(uev_t *w, void *arg, int events)
+{
+	struct timeval tv;
+
+	gettimeofday(&tv, NULL);
+	printf("Cron job HELO %s", ctime(&tv.tv_sec));
+}
+
+int main(void)
+{
+	uev_t cron_watcher;
+	uev_ctx_t ctx;
+	time_t when, interval;
+	struct timeval tv;
+
+	/* Initialize libuEv */
+	uev_init(&ctx);
+
+	/* Cron job */
+	gettimeofday(&tv, NULL);
+	when     = tv.tv_sec + 30;
+	interval = 30;
+	uev_cron_init(&ctx, &cron_watcher, cron_job, NULL, when, interval);
+
+	/* Start event loop */
+	printf("Start of test %s", ctime(&tv.tv_sec));
+	printf("Expected cron %s", ctime(&when));
+
+	return uev_run(&ctx, 0);
+}
+
+/**
+ * Local Variables:
+ *  indent-tabs-mode: t
+ *  c-file-style: "linux"
+ * End:
+ */