fixes #308 Close can block

Ultimately, this just removes the support for lingering altogether.
Based on prior experience, lingering has always been unreliable, and
was removed in legacy libnanomsg ages ago.

The problem is that operating system support for lingering is very
inconsistent at best, and for some transports the very concept is somewhat
meaningless.

Making things worse, we were never able to adequately capture an exit()
event from another thread -- so lingering was always a false promise.

Applications that need to be sure that messages are delivered should
either include an ack in their protocol, use req/rep (which has an ack),
or inject a suitable delay of their own.

For things going over local networks, an extra delay of 100 msec should
be sufficient *most of the time*.

1 files changed, 10 insertions, 56 deletions

diff --git a/src/core/msgqueue.c b/src/core/msgqueue.c
index 8246279f..529e7f4d 100644
--- a/src/core/msgqueue.c
+++ b/src/core/msgqueue.c
@@ -17,7 +17,6 @@
 
 struct nni_msgq {
 	nni_mtx   mq_lock;
-	nni_cv    mq_drained;
 	int       mq_cap;
 	int       mq_alloc; // alloc is cap + 2...
 	int       mq_len;
@@ -26,7 +25,6 @@ struct nni_msgq {
 	int       mq_closed;
 	int       mq_puterr;
 	int       mq_geterr;
-	int       mq_draining;
 	int       mq_besteffort;
 	nni_msg **mq_msgs;
 
@@ -68,18 +66,16 @@ nni_msgq_init(nni_msgq **mqp, unsigned cap)
 	nni_aio_list_init(&mq->mq_aio_putq);
 	nni_aio_list_init(&mq->mq_aio_getq);
 	nni_mtx_init(&mq->mq_lock);
-	nni_cv_init(&mq->mq_drained, &mq->mq_lock);
-
-	mq->mq_cap      = cap;
-	mq->mq_alloc    = alloc;
-	mq->mq_len      = 0;
-	mq->mq_get      = 0;
-	mq->mq_put      = 0;
-	mq->mq_closed   = 0;
-	mq->mq_puterr   = 0;
-	mq->mq_geterr   = 0;
-	mq->mq_draining = 0;
-	*mqp            = mq;
+
+	mq->mq_cap    = cap;
+	mq->mq_alloc  = alloc;
+	mq->mq_len    = 0;
+	mq->mq_get    = 0;
+	mq->mq_put    = 0;
+	mq->mq_closed = 0;
+	mq->mq_puterr = 0;
+	mq->mq_geterr = 0;
+	*mqp          = mq;
 
 	return (0);
 }
@@ -92,7 +88,6 @@ nni_msgq_fini(nni_msgq *mq)
 	if (mq == NULL) {
 		return;
 	}
-	nni_cv_fini(&mq->mq_drained);
 	nni_mtx_fini(&mq->mq_lock);
 
 	/* Free any orphaned messages. */
@@ -317,12 +312,6 @@ nni_msgq_run_notify(nni_msgq *mq)
 		}
 		mq->mq_cb_fn(mq->mq_cb_arg, flags);
 	}
-
-	if (mq->mq_draining) {
-		if ((mq->mq_len == 0) && !nni_list_empty(&mq->mq_aio_putq)) {
-			nni_cv_wake(&mq->mq_drained);
-		}
-	}
 }
 
 void
@@ -438,40 +427,6 @@ nni_msgq_tryput(nni_msgq *mq, nni_msg *msg)
 }
 
 void
-nni_msgq_drain(nni_msgq *mq, nni_time expire)
-{
-	nni_aio *aio;
-
-	nni_mtx_lock(&mq->mq_lock);
-	mq->mq_closed   = 1;
-	mq->mq_draining = 1;
-	while ((mq->mq_len > 0) || !nni_list_empty(&mq->mq_aio_putq)) {
-		if (nni_cv_until(&mq->mq_drained, expire) != 0) {
-			break;
-		}
-	}
-
-	// Timed out or writers drained.
-
-	// Complete the putq as NNG_ECLOSED.
-	while ((aio = nni_list_first(&mq->mq_aio_putq)) != NULL) {
-		nni_aio_list_remove(aio);
-		nni_aio_finish_error(aio, NNG_ECLOSED);
-	}
-
-	// Free any remaining messages in the queue.
-	while (mq->mq_len > 0) {
-		nni_msg *msg = mq->mq_msgs[mq->mq_get++];
-		if (mq->mq_get >= mq->mq_alloc) {
-			mq->mq_get = 0;
-		}
-		mq->mq_len--;
-		nni_msg_free(msg);
-	}
-	nni_mtx_unlock(&mq->mq_lock);
-}
-
-void
 nni_msgq_close(nni_msgq *mq)
 {
 	nni_aio *aio;
@@ -585,7 +540,6 @@ nni_msgq_resize(nni_msgq *mq, int cap)
 
 out:
 	// Wake everyone up -- we changed everything.
-	nni_cv_wake(&mq->mq_drained);
 	nni_mtx_unlock(&mq->mq_lock);
 	return (0);
 }