From cd2c02cefddee94e0142a8f1d3d156c05c58472a Mon Sep 17 00:00:00 2001
From: Sebastian Harl <sh@tokkee.org>
Date: Mon, 21 Oct 2013 09:10:08 +0200
Subject: [PATCH] utils channel: Added sdb_channel_shutdown().

This function initiates a shutdown of the channel, forbidding any subsequent
writes. However, readers are still able to empty the buffer. Then, EBADF will
be returned through errno. This allows for graceful shutdowns.
---
 src/include/utils/channel.h | 12 ++++++++++++
 src/utils/channel.c         | 19 ++++++++++++++++++-
 2 files changed, 30 insertions(+), 1 deletion(-)

diff --git a/src/include/utils/channel.h b/src/include/utils/channel.h
index e1b3f0e..49d37fd 100644
--- a/src/include/utils/channel.h
+++ b/src/include/utils/channel.h
@@ -108,6 +108,18 @@ int
 sdb_channel_select(sdb_channel_t *chan, int *wantread, void *read_data,
 		int *wantwrite, void *write_data, const struct timespec *timeout);
 
+/* sdb_channel_shutdown:
+ * Initiate a shutdown of the channel. Any subsequent writes will fail. Read
+ * operations will still be possible until the channel buffer is empty and
+ * then fail as well. Failing operations set errno to EBADF.
+ *
+ * Returns:
+ *  - 0 on success
+ *  - a negative value else
+ */
+int
+sdb_channel_shutdown(sdb_channel_t *chan);
+
 #ifdef __cplusplus
 } /* extern "C" */
 #endif
diff --git a/src/utils/channel.c b/src/utils/channel.c
index 8e55ae5..a45247a 100644
--- a/src/utils/channel.c
+++ b/src/utils/channel.c
@@ -57,6 +57,8 @@ struct sdb_channel {
 	size_t head;
 	size_t tail;
 	_Bool full;
+
+	_Bool shutdown;
 };
 
 /*
@@ -79,7 +81,7 @@ channel_write(sdb_channel_t *chan, const void *data)
 {
 	assert(chan);
 
-	if (chan->full)
+	if (chan->full || chan->shutdown)
 		return -1;
 	else if (! data)
 		return 0;
@@ -199,6 +201,12 @@ sdb_channel_select(sdb_channel_t *chan, int *wantread, void *read_data,
 				break;
 		}
 
+		if (chan->shutdown) {
+			if (read_status)
+				status = EBADF;
+			break;
+		}
+
 		if (timeout) {
 			struct timespec abstime;
 
@@ -258,5 +266,14 @@ sdb_channel_read(sdb_channel_t *chan, void *data)
 	return status;
 } /* sdb_channel_read */
 
+int
+sdb_channel_shutdown(sdb_channel_t *chan)
+{
+	if (! chan)
+		return -1;
+	chan->shutdown = 1;
+	return 0;
+} /* sdb_channel_shutdown */
+
 /* vim: set tw=78 sw=4 ts=4 noexpandtab : */
 
-- 
2.30.2