libvirt/examples/domain-events/events-python/event-test.py
Daniel P. Berrange 93f77250b3 Rewrite example domain events programm for python
The existing python demo for domain events does not fully
implement the event loop contract. This makes the code useless
for real world applications. This change re-writes the demo so
that it has a full event loop implementation which is suitable
for application usage & better demonstrates integration

* examples/domain-events/events-python/event-test.py: Rewrite
  to include a real world usable event loop implementation
2009-10-09 13:05:10 +01:00

466 lines
16 KiB
Python

#!/usr/bin/python -u
#
#
#
#################################################################################
# Start off by implementing a general purpose event loop for anyones use
#################################################################################
import sys
import getopt
import os
import libvirt
import select
import errno
import time
import threading
#
# This general purpose event loop will support waiting for file handle
# I/O and errors events, as well as scheduling repeatable timers with
# a fixed interval.
#
# It is a pure python implementation based around the poll() API
#
class virEventLoopPure:
# This class contains the data we need to track for a
# single file handle
class virEventLoopPureHandle:
def __init__(self, handle, fd, events, cb, opaque):
self.handle = handle
self.fd = fd
self.events = events
self.cb = cb
self.opaque = opaque
def get_id(self):
return self.handle
def get_fd(self):
return self.fd
def get_events(self):
return self.events
def set_events(self, events):
self.events = events
def dispatch(self, events):
self.cb(self.handle,
self.fd,
events,
self.opaque[0],
self.opaque[1])
# This class contains the data we need to track for a
# single periodic timer
class virEventLoopPureTimer:
def __init__(self, timer, interval, cb, opaque):
self.timer = timer
self.interval = interval
self.cb = cb
self.opaque = opaque
self.lastfired = 0
def get_id(self):
return self.timer
def get_interval(self):
return self.interval
def set_interval(self, interval):
self.interval = interval
def get_last_fired(self):
return self.lastfired
def set_last_fired(self, now):
self.lastfired = now
def dispatch(self):
self.cb(self.timer,
self.opaque[0],
self.opaque[1])
def __init__(self, debug=False):
self.debugOn = debug
self.poll = select.poll()
self.pipetrick = os.pipe()
self.nextHandleID = 1
self.nextTimerID = 1
self.handles = []
self.timers = []
self.quit = False
# The event loop can be used from multiple threads at once.
# Specifically while the main thread is sleeping in poll()
# waiting for events to occur, another thread may come along
# and add/update/remove a file handle, or timer. When this
# happens we need to interrupt the poll() sleep in the other
# thread, so that it'll see the file handle / timer changes.
#
# Using OS level signals for this is very unreliable and
# hard to implement correctly. Thus we use the real classic
# "self pipe" trick. A anonymous pipe, with one end registered
# with the event loop for input events. When we need to force
# the main thread out of a poll() sleep, we simple write a
# single byte of data to the other end of the pipe.
self.debug("Self pipe watch %d write %d" %(self.pipetrick[0], self.pipetrick[1]))
self.poll.register(self.pipetrick[0], select.POLLIN)
def debug(self, msg):
if self.debugOn:
print msg
# Calculate when the next timeout is due to occurr, returning
# the absolute timestamp for the next timeout, or 0 if there is
# no timeout due
def next_timeout(self):
next = 0
for t in self.timers:
last = t.get_last_fired()
interval = t.get_interval()
if interval < 0:
continue
if next == 0 or (last + interval) < next:
next = last + interval
return next
# Lookup a virEventLoopPureHandle object based on file descriptor
def get_handle_by_fd(self, fd):
for h in self.handles:
if h.get_fd() == fd:
return h
return None
# Lookup a virEventLoopPureHandle object based on its event loop ID
def get_handle_by_id(self, handleID):
for h in self.handles:
if h.get_id() == handleID:
return h
return None
# This is the heart of the event loop, performing one single
# iteration. It asks when the next timeout is due, and then
# calcuates the maximum amount of time it is able to sleep
# for in poll() pending file handle events.
#
# It then goes into the poll() sleep.
#
# When poll() returns, there will zero or more file handle
# events which need to be dispatched to registered callbacks
# It may also be time to fire some periodic timers.
#
# Due to the coarse granularity of schedular timeslices, if
# we ask for a sleep of 500ms in order to satisfy a timer, we
# may return upto 1 schedular timeslice early. So even though
# our sleep timeout was reached, the registered timer may not
# technically be at its expiry point. This leads to us going
# back around the loop with a crazy 5ms sleep. So when checking
# if timeouts are due, we allow a margin of 20ms, to avoid
# these pointless repeated tiny sleeps.
def run_once(self):
sleep = -1
next = self.next_timeout()
self.debug("Next timeout due at %d" % next)
if next > 0:
now = int(time.time() * 1000)
if now >= next:
sleep = 0
else:
sleep = next - now
self.debug("Poll with a sleep of %d" % sleep)
events = self.poll.poll(sleep / 1000.0)
# Dispatch any file handle events that occurred
for (fd, revents) in events:
# See if the events was from the self-pipe
# telling us to wakup. if so, then discard
# the data just continue
if fd == self.pipetrick[0]:
data = os.read(fd, 1)
continue
h = self.get_handle_by_fd(fd)
if h:
self.debug("Dispatch fd %d handle %d events %d" % (fd, h.get_id(), revents))
h.dispatch(self.events_from_poll(revents))
now = int(time.time() * 1000)
for t in self.timers:
interval = t.get_interval()
if interval < 0:
continue
want = t.get_last_fired() + interval
# Deduct 20ms, since schedular timeslice
# means we could be ever so slightly early
if now >= (want-20):
self.debug("Dispatch timer %d now %s want %s" % (t.get_id(), str(now), str(want)))
t.set_last_fired(now)
t.dispatch()
# Actually the event loop forever
def run_loop(self):
self.quit = False
while not self.quit:
self.run_once()
def interrupt(self):
os.write(self.pipetrick[1], 'c')
# Registers a new file handle 'fd', monitoring for 'events' (libvirt
# event constants), firing the callback cb() when an event occurs.
# Returns a unique integer identier for this handle, that should be
# used to later update/remove it
def add_handle(self, fd, events, cb, opaque):
handleID = self.nextHandleID + 1
self.nextHandleID = self.nextHandleID + 1
h = self.virEventLoopPureHandle(handleID, fd, events, cb, opaque)
self.handles.append(h)
self.poll.register(fd, self.events_to_poll(events))
self.interrupt()
self.debug("Add handle %d fd %d events %d" % (handleID, fd, events))
return handleID
# Registers a new timer with periodic expiry at 'interval' ms,
# firing cb() each time the timer expires. If 'interval' is -1,
# then the timer is registered, but not enabled
# Returns a unique integer identier for this handle, that should be
# used to later update/remove it
def add_timer(self, interval, cb, opaque):
timerID = self.nextTimerID + 1
self.nextTimerID = self.nextTimerID + 1
h = self.virEventLoopPureTimer(timerID, interval, cb, opaque)
self.timers.append(h)
self.interrupt()
self.debug("Add timer %d interval %d" % (timerID, interval))
return timerID
# Change the set of events to be monitored on the file handle
def update_handle(self, handleID, events):
h = self.get_handle_by_id(handleID)
if h:
h.set_events(events)
self.poll.unregister(h.get_fd())
self.poll.register(h.get_fd(), self.events_to_poll(events))
self.interrupt()
self.debug("Update handle %d fd %d events %d" % (handleID, h.get_fd(), events))
# Change the periodic frequency of the timer
def update_timer(self, timerID, interval):
for h in self.timers:
if h.get_id() == timerID:
h.set_interval(interval);
self.interrupt()
self.debug("Update timer %d interval %d" % (timerID, interval))
break
# Stop monitoring for events on the file handle
def remove_handle(self, handleID):
handles = []
for h in self.handles:
if h.get_id() == handleID:
self.poll.unregister(h.get_fd())
self.debug("Remove handle %d fd %d" % (handleID, h.get_fd()))
else:
handles.append(h)
self.handles = handles
self.interrupt()
# Stop firing the periodic timer
def remove_timer(self, timerID):
timers = []
for h in self.timers:
if h.get_id() != timerID:
timers.append(h)
self.debug("Remove timer %d" % timerID)
self.timers = timers
self.interrupt()
# Convert from libvirt event constants, to poll() events constants
def events_to_poll(self, events):
ret = 0
if events & libvirt.VIR_EVENT_HANDLE_READABLE:
ret |= select.POLLIN
if events & libvirt.VIR_EVENT_HANDLE_WRITABLE:
ret |= select.POLLOUT
if events & libvirt.VIR_EVENT_HANDLE_ERROR:
ret |= select.POLLERR;
if events & libvirt.VIR_EVENT_HANDLE_HANGUP:
ret |= select.POLLHUP;
return ret
# Convert from poll() event constants, to libvirt events constants
def events_from_poll(self, events):
ret = 0;
if events & select.POLLIN:
ret |= libvirt.VIR_EVENT_HANDLE_READABLE;
if events & select.POLLOUT:
ret |= libvirt.VIR_EVENT_HANDLE_WRITABLE;
if events & select.POLLNVAL:
ret |= libvirt.VIR_EVENT_HANDLE_ERROR;
if events & select.POLLERR:
ret |= libvirt.VIR_EVENT_HANDLE_ERROR;
if events & select.POLLHUP:
ret |= libvirt.VIR_EVENT_HANDLE_HANGUP;
return ret;
###########################################################################
# Now glue an instance of the general event loop into libvirt's event loop
###########################################################################
# This single global instance of the event loop wil be used for
# monitoring libvirt events
eventLoop = virEventLoopPure(debug=False)
# This keeps track of what thread is running the event loop,
# (if it is run in a background thread)
eventLoopThread = None
# These next set of 6 methods are the glue between the official
# libvirt events API, and our particular impl of the event loop
#
# There is no reason why the 'virEventLoopPure' has to be used.
# An application could easily may these 6 glue methods hook into
# another event loop such as GLib's, or something like the python
# Twisted event framework.
def virEventAddHandleImpl(fd, events, cb, opaque):
global eventLoop
return eventLoop.add_handle(fd, events, cb, opaque)
def virEventUpdateHandleImpl(handleID, events):
global eventLoop
return eventLoop.update_handle(handleID, events)
def virEventRemoveHandleImpl(handleID):
global eventLoop
return eventLoop.remove_handle(handleID)
def virEventAddTimerImpl(interval, cb, opaque):
global eventLoop
return eventLoop.add_timer(interval, cb, opaque)
def virEventUpdateTimerImpl(timerID, interval):
global eventLoop
return eventLoop.update_timer(timerID, interval)
def virEventRemoveTimerImpl(timerID):
global eventLoop
return eventLoop.remove_timer(timerID)
# This tells libvirt what event loop implementation it
# should use
def virEventLoopPureRegister():
libvirt.virEventRegisterImpl(virEventAddHandleImpl,
virEventUpdateHandleImpl,
virEventRemoveHandleImpl,
virEventAddTimerImpl,
virEventUpdateTimerImpl,
virEventRemoveTimerImpl)
# Directly run the event loop in the current thread
def virEventLoopPureRun():
global eventLoop
eventLoop.run_loop()
# Spawn a background thread to run the event loop
def virEventLoopPureStart():
global eventLoopThread
virEventLoopPureRegister()
eventLoopThread = threading.Thread(target=virEventLoopPureRun, name="libvirtEventLoop")
eventLoopThread.setDaemon(True)
eventLoopThread.start()
##########################################################################
# Everything that now follows is a simple demo of domain lifecycle events
##########################################################################
def eventToString(event):
eventStrings = ( "Added",
"Removed",
"Started",
"Suspended",
"Resumed",
"Stopped",
"Saved",
"Restored" );
return eventStrings[event];
def myDomainEventCallback1 (conn, dom, event, detail, opaque):
print "myDomainEventCallback1 EVENT: Domain %s(%s) %s %d" % (dom.name(), dom.ID(), eventToString(event), detail)
def myDomainEventCallback2 (conn, dom, event, detail, opaque):
print "myDomainEventCallback2 EVENT: Domain %s(%s) %s %d" % (dom.name(), dom.ID(), eventToString(event), detail)
def usage():
print "usage: "+os.path.basename(sys.argv[0])+" [uri]"
print " uri will default to qemu:///system"
def main():
try:
opts, args = getopt.getopt(sys.argv[1:], "h", ["help"] )
except getopt.GetoptError, err:
# print help information and exit:
print str(err) # will print something like "option -a not recognized"
usage()
sys.exit(2)
for o, a in opts:
if o in ("-h", "--help"):
usage()
sys.exit()
if len(sys.argv) > 1:
uri = sys.argv[1]
else:
uri = "qemu:///system"
print "Using uri:" + uri
# Run a background thread with the event loop
virEventLoopPureStart()
vc = libvirt.open(uri)
# Close connection on exit (to test cleanup paths)
old_exitfunc = getattr(sys, 'exitfunc', None)
def exit():
print "Closing " + str(vc)
vc.close()
if (old_exitfunc): old_exitfunc()
sys.exitfunc = exit
#Add 2 callbacks to prove this works with more than just one
vc.domainEventRegister(myDomainEventCallback1,None)
vc.domainEventRegister(myDomainEventCallback2,None)
# The rest of your app would go here normally, but for sake
# of demo we'll just go to sleep. The other option is to
# run the event loop in your main thread if your app is
# totally event based.
while 1:
time.sleep(1)
if __name__ == "__main__":
main()