evwatch: Add "prepare" and "check" watchers.

Adds two new callbacks: "prepare" watchers, which fire immediately
before we poll for I/O, and "check" watchers, which fire immediately
after we finish polling and before we process events. This allows other
event loops to be embedded into libevent's, and enables certain
performance monitoring.

Closes: #710

1 files changed, 82 insertions, 0 deletions

diff --git a/watch.c b/watch.c
new file mode 100644
index 00000000..645cbd9a
--- /dev/null
+++ b/watch.c
@@ -0,0 +1,82 @@
+/*
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ * 3. The name of the author may not be used to endorse or promote products
+ *    derived from this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
+ * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
+ * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
+ * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
+ * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
+ * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include "event2/watch.h"
+#include "event-internal.h"
+#include "evthread-internal.h"
+
+static inline struct evwatch *
+evwatch_new(struct event_base *base, union evwatch_cb callback, void *arg, unsigned type)
+{
+	struct evwatch *watcher = mm_malloc(sizeof(struct evwatch));
+	if (!watcher)
+		return NULL;
+	watcher->base = base;
+	watcher->type = type;
+	watcher->callback = callback;
+	watcher->arg = arg;
+	EVBASE_ACQUIRE_LOCK(base, th_base_lock);
+	TAILQ_INSERT_TAIL(&base->watchers[type], watcher, next);
+	EVBASE_RELEASE_LOCK(base, th_base_lock);
+	return watcher;
+}
+
+struct evwatch *
+evwatch_prepare_new(struct event_base *base, evwatch_prepare_cb callback, void *arg)
+{
+	union evwatch_cb cb = { .prepare = callback };
+	return evwatch_new(base, cb, arg, EVWATCH_PREPARE);
+}
+
+struct evwatch *
+evwatch_check_new(struct event_base *base, evwatch_check_cb callback, void *arg)
+{
+	union evwatch_cb cb = { .check = callback };
+	return evwatch_new(base, cb, arg, EVWATCH_CHECK);
+}
+
+struct event_base *
+evwatch_base(struct evwatch *watcher)
+{
+	return watcher->base;
+}
+
+void
+evwatch_free(struct evwatch *watcher)
+{
+	EVBASE_ACQUIRE_LOCK(watcher->base, th_base_lock);
+	TAILQ_REMOVE(&watcher->base->watchers[watcher->type], watcher, next);
+	EVBASE_RELEASE_LOCK(watcher->base, th_base_lock);
+	mm_free(watcher);
+}
+
+int
+evwatch_prepare_get_timeout(const struct evwatch_prepare_cb_info *info, struct timeval *timeout)
+{
+	if (info->timeout) {
+		*timeout = *(info->timeout);
+		return 1;
+	}
+	return 0;
+}