[libvirt] [PATCH] Prevent overfilling of self-pipe in python event loop

[Daniel Veillard]

On Thu, Jan 27, 2011 at 12:56:24PM +0000, Daniel P. Berrange wrote:
> If the event loop takes a very long time todo something, it is
> possible for the 'self pipe' buffer to become full at which
> point the entire event loop + remote driver deadlock. Use a
> boolean flag to ensure we have strict one-in, one-out behaviour
> on writes/reads of the 'self pipe'
> ---
>  examples/domain-events/events-python/event-test.py |   10 +++++++++-
>  1 files changed, 9 insertions(+), 1 deletions(-)
> 
> diff --git a/examples/domain-events/events-python/event-test.py b/examples/domain-events/events-python/event-test.py
> index 903f934..c149ed9 100644
> --- a/examples/domain-events/events-python/event-test.py
> +++ b/examples/domain-events/events-python/event-test.py
> @@ -92,6 +92,8 @@ class virEventLoopPure:
>      def __init__(self):
>          self.poll = select.poll()
>          self.pipetrick = os.pipe()
> +        self.pendingWakeup = False
> +        self.runningPoll = False
>          self.nextHandleID = 1
>          self.nextTimerID = 1
>          self.handles = []
> @@ -166,6 +168,7 @@ class virEventLoopPure:
>      # these pointless repeated tiny sleeps.
>      def run_once(self):
>          sleep = -1
> +        self.runningPoll = True
>          next = self.next_timeout()
>          debug("Next timeout due at %d" % next)
>          if next > 0:
> @@ -184,6 +187,7 @@ class virEventLoopPure:
>              # telling us to wakup. if so, then discard
>              # the data just continue
>              if fd == self.pipetrick[0]:
> +                self.pendingWakeup = False
>                  data = os.read(fd, 1)
>                  continue
>  
> @@ -206,6 +210,8 @@ class virEventLoopPure:
>                  t.set_last_fired(now)
>                  t.dispatch()
>  
> +        self.runningPoll = False
> +
>  
>      # Actually the event loop forever
>      def run_loop(self):
> @@ -214,7 +220,9 @@ class virEventLoopPure:
>              self.run_once()
>  
>      def interrupt(self):
> -        os.write(self.pipetrick[1], 'c')
> +        if self.runningPoll and not self.pendingWakeup:
> +            self.pendingWakeup = True
> +            os.write(self.pipetrick[1], 'c')
>  
>  
>      # Registers a new file handle 'fd', monitoring  for 'events' (libvirt

  ACK,

Daniel

-- 
Daniel Veillard      | libxml Gnome XML XSLT toolkit  http://xmlsoft.org/
daniel at veillard.com  | Rpmfind RPM search engine http://rpmfind.net/
http://veillard.com/ | virtualization library  http://libvirt.org/