[Cluster-devel] [PATCH] glocktop: Fix a tight loop under nohup

[Andrew Price]

When glocktop is run under nohup, it redirects /dev/null to stdin, which
flags up EOF and causes the file descriptor to always be in a ready
state when select()ed. This causes select() to return immediately
instead of timing out after the refresh delay.

Make sure to sleep for the refresh delay on EOF to avoid getting into a
tight loop when running under nohup.

Signed-off-by: Andrew Price <anprice at redhat.com>
---
 gfs2/glocktop/glocktop.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/gfs2/glocktop/glocktop.c b/gfs2/glocktop/glocktop.c
index 43c3c3f..fe6bcc2 100644
--- a/gfs2/glocktop/glocktop.c
+++ b/gfs2/glocktop/glocktop.c
@@ -1856,6 +1856,15 @@ int main(int argc, char **argv)
 				if (refresh_time < 1)
 					refresh_time = 1;
 				break;
+			/* We can get an EOF if the user hits ^D or if
+			   /dev/null is redirected to stdin, such as when
+			   running under nohup. It should be safe to assume the
+			   latter since ^D shouldn't be expected to do anything
+			   useful. In that case, select() returns immediately
+			   so we need to enforce the refresh delay with a sleep */
+			case EOF:
+				sleep(refresh_time);
+				break;
 			}
 		}
 		iters_done++;
-- 
2.4.3