lib/nfs/Connection: detect libnfs reconnect

When rpc_reconnect_requeue() gets called from inside nfs_service(), the NfsInputStream can stall completely because the old socket has been unregistered from epoll automatically, but the new one has never been registered. Therefore, nfs_service() will never be called again. This kludge attempts to detect this condition by checking nfs_which_events()==POLLOUT. https://bugs.musicpd.org/view.php?id=4081

lib/nfs/Connection: detect libnfs reconnect
05eac20f · Max Kellermann · 38d263ac · 05eac20f · 05eac20f
Commit 05eac20f authored Feb 01, 2017 by Max Kellermann
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NEWS NEWS +2 -0

Connection.cxx src/lib/nfs/Connection.cxx +12 -1

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--- a/NEWS
+++ b/NEWS
 ver 0.20.4 (not yet released)
+* input
+  - nfs: fix freeze after reconnect
 * output
  - sndio: work around a libroar C++ incompatibility
 * workaround for GCC 4.9 "constexpr" bug

--- a/src/lib/nfs/Connection.cxx
+++ b/src/lib/nfs/Connection.cxx
@@ -396,6 +396,17 @@ NfsConnection::ScheduleSocket()
 	assert(GetEventLoop().IsInside());
 	assert(context != nullptr);

+	const int which_events = nfs_which_events(context);
+
+	if (which_events == POLLOUT && SocketMonitor::IsDefined())
+		/* kludge: if libnfs asks only for POLLOUT, it means
+		   that it is currently waiting for the connect() to
+		   finish - rpc_reconnect_requeue() may have been
+		   called from inside nfs_service(); we must now
+		   unregister the old socket and register the new one
+		   instead */
+		SocketMonitor::Steal();
+
 	if (!SocketMonitor::IsDefined()) {
 		int _fd = nfs_get_fd(context);
 		if (_fd < 0)
@@ -405,7 +416,7 @@ NfsConnection::ScheduleSocket()
 		SocketMonitor::Open(_fd);
 	}

-	SocketMonitor::Schedule(libnfs_to_events(nfs_which_events(context)));
+	SocketMonitor::Schedule(libnfs_to_events(which_events));
 }

 inline int