Implement a simple wait queue API. The idea is to allow multiple "waiters"

to wait on the same "tag" for a deferred result.

A waiter is a callback and a void *argument.  The first waiter (the one for
which waitq_wait() returns true) is supposed to run some code that leads to
waitq_run() being run, which will destroy that waitq and call all callbacks
in turn.

Not used at the moment, but will be soon.

ok gilles@ chl@

2 files changed, 105 insertions, 1 deletions

diff --git a/usr.sbin/smtpd/smtpd.h b/usr.sbin/smtpd/smtpd.h
index 0011942ed9a..d508227392c 100644
--- a/usr.sbin/smtpd/smtpd.h
+++ b/usr.sbin/smtpd/smtpd.h
@@ -1,4 +1,4 @@
-/*	$OpenBSD: smtpd.h,v 1.379 2012/10/07 15:46:38 chl Exp $	*/
+/*	$OpenBSD: smtpd.h,v 1.380 2012/10/07 17:21:37 eric Exp $	*/
 
 /*
  * Copyright (c) 2008 Gilles Chehade <gilles@openbsd.org>
@@ -1170,3 +1170,7 @@ void log_envelope(const struct envelope *, const char *, const char *);
 void session_socket_blockmode(int, enum blockmodes);
 void session_socket_no_linger(int);
 int session_socket_error(int);
+
+/* waitq.c */
+int  waitq_wait(void *, void (*)(void *, void *, void *), void *);
+void waitq_run(void *, void *);
diff --git a/usr.sbin/smtpd/waitq.c b/usr.sbin/smtpd/waitq.c
new file mode 100644
index 00000000000..da6519a6506
--- /dev/null
+++ b/usr.sbin/smtpd/waitq.c
@@ -0,0 +1,100 @@
+/*	$OpenBSD: waitq.c,v 1.1 2012/10/07 17:21:37 eric Exp $	*/
+
+/*
+ * Copyright (c) 2012 Eric Faurot <eric@openbsd.org>
+ *
+ * Permission to use, copy, modify, and distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+ * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ */
+
+#include <sys/types.h>
+#include <sys/tree.h>
+#include <sys/queue.h>
+#include <sys/uio.h>
+
+#include <imsg.h>
+#include <stdio.h>
+#include <stdlib.h>
+
+#include "smtpd.h"
+
+struct waiter {
+	TAILQ_ENTRY(waiter)	 entry;
+	void			(*cb)(void *, void *, void *);
+	void			*arg;
+};
+
+struct waitq {
+	SPLAY_ENTRY(waitq)	 entry;
+	void			*tag;
+	TAILQ_HEAD(, waiter)	 waiters;
+};
+
+static int waitq_cmp(struct waitq *, struct waitq *);
+
+SPLAY_HEAD(waitqtree, waitq);
+SPLAY_PROTOTYPE(waitqtree, waitq, entry, waitq_cmp);
+
+static struct waitqtree waitqs = SPLAY_INITIALIZER(&waitqs);
+
+static int
+waitq_cmp(struct waitq *a, struct waitq *b)
+{
+	if (a->tag < b->tag)
+		return (-1);
+	if (a->tag > b->tag)
+		return (1);
+	return (0);
+}
+
+SPLAY_GENERATE(waitqtree, waitq, entry, waitq_cmp);
+
+int
+waitq_wait(void *tag, void (*cb)(void *, void *, void *), void *arg)
+{
+	struct waitq	*wq, key;
+	struct waiter	*w;
+
+	key.tag = tag;
+	wq = SPLAY_FIND(waitqtree, &waitqs, &key);
+	if (wq == NULL) {
+		wq = xmalloc(sizeof *wq, "waitq_wait");
+		wq->tag = tag;
+		TAILQ_INIT(&wq->waiters);
+		SPLAY_INSERT(waitqtree, &waitqs, wq);
+	}
+
+	w = xmalloc(sizeof *w, "waitq_wait");
+	w->cb = cb;
+	w->arg = arg;
+	TAILQ_INSERT_TAIL(&wq->waiters, w, entry);
+
+	return (w == TAILQ_FIRST(&wq->waiters));
+}
+
+void
+waitq_run(void *tag, void *result)
+{
+	struct waitq	*wq, key;
+	struct waiter	*w;
+
+	key.tag = tag;
+	wq = SPLAY_FIND(waitqtree, &waitqs, &key);
+	SPLAY_REMOVE(waitqtree, &waitqs, wq);
+
+	while((w = TAILQ_FIRST(&wq->waiters))) {
+		TAILQ_REMOVE(&wq->waiters, w, entry);
+		w->cb(tag, w->arg, result);
+		free(w);
+	}
+	free(wq);
+}