From f24e70a435a9eb8acd7ce85fc3b411a63a6b14be Mon Sep 17 00:00:00 2001
From: Bob Lantz <rlantz@cs.stanford.edu>
Date: Mon, 12 Apr 2010 18:33:20 -0700
Subject: [PATCH] Added timeout option for monitor().

This allows monitor() to be used for polling. Of course, you
probably want to use poll() first anyway, but it's nice not
to have to block if there's no output.
---
 mininet/node.py | 23 ++++++++++++++---------
 1 file changed, 14 insertions(+), 9 deletions(-)

diff --git a/mininet/node.py b/mininet/node.py
index aab7e53..77696a5 100644
--- a/mininet/node.py
+++ b/mininet/node.py
@@ -149,10 +149,11 @@ class Node( object ):
         "Stop node."
         self.terminate()
 
-    def waitReadable( self ):
-        "Wait until node's output is readable."
+    def waitReadable( self, timeoutms=None ):
+        """Wait until node's output is readable.
+           timeoutms: timeout in ms or None to wait indefinitely."""
         if len( self.readbuf ) == 0:
-            self.pollOut.poll()
+            self.pollOut.poll( timeoutms )
 
     def sendCmd( self, cmd, printPid=True ):
         """Send a command, followed by a command to echo a sentinel,
@@ -160,6 +161,9 @@ class Node( object ):
         assert not self.waiting
         if isinstance( cmd, list ):
             cmd = ' '.join( cmd )
+        if not re.search( r'\w', cmd ):
+            # Replace empty commands with something harmless
+            cmd = 'echo -n'
         if len( cmd ) > 0 and cmd[ -1 ] == '&':
             separator = '&'
             cmd = cmd[ :-1 ]
@@ -180,11 +184,12 @@ class Node( object ):
             except Exception:
                 pass
 
-    def monitor( self ):
+    def monitor( self, timeoutms=None ):
         """Monitor and return the output of a command.
-           Set self.waiting to False if command has completed."""
+           Set self.waiting to False if command has completed.
+           timeoutms: timeout in ms or None to wait indefinitely."""
         assert self.waiting
-        self.waitReadable()
+        self.waitReadable( timeoutms )
         data = self.read( 1024 )
         # Look for PID
         marker = chr( 1 ) + r'\d+\n'
@@ -395,10 +400,10 @@ class Switch( Node ):
             error( '*** Error: %s has execed and cannot accept commands' %
                      self.name )
 
-    def monitor( self ):
-        "Monitor node."
+    def monitor( self, *args, **kwargs ):
+        "Monitor a switch."
         if not self.execed:
-            return Node.monitor( self )
+            return Node.monitor( self, *args, **kwargs )
         else:
             return True, ''