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+# Module sched -- a generally useful event scheduler class
+
+# Each instance of this class manages its own queue.
+# No multi-threading is implied; you are supposed to hack that
+# yourself, or use a single instance per application.
+#
+# Each instance is parametrized with two functions, one that is
+# supposed to return the current time, one that is supposed to
+# implement a delay.  You can implement fine- or course-grained
+# real-time scheduling by substituting time and sleep or millitimer
+# and millisleep from the built-in module time, or you can implement
+# simulated time by writing your own functions.  This can also be
+# used to integrate scheduling with STDWIN events; the delay function
+# is allowed to modify the queue.  Time can be expressed
+# as integers or floating point numbers, as long as it is consistent.
+
+# Events are specified by tuples (time, priority, action, argument).
+# As in UNIX, lower priority numbers mean higher priority; in this
+# way the queue can be maintained fully sorted.  Execution of the
+# event means calling the action function, passing it the argument.
+# Remember that in Python, multiple function arguments can be packed
+# in a tuple.   The action function may be an instance method so it
+# has another way to reference private data (besides global variables).
+# Parameterless functions or methods cannot be used, however.
+
+class scheduler():
+	#
+	# Initialize a new instance, passing the time and delay functions
+	#
+	def init(self, (timefunc, delayfunc)):
+		self.queue = []
+		self.timefunc = timefunc
+		self.delayfunc = delayfunc
+		return self
+	#
+	# Enter a new event in the queue at an absolute time.
+	# Returns an ID for the event which can be used
+	# to remove it, if necessary.
+	#
+	def enterabs(self, event):
+		time, priority, action, argument = event
+		q = self.queue
+		# XXX Could use bisection or linear interpolation?
+		for i in range(len(q)):
+			qtime, qpri, qact, qarg = q[i]
+			if time < qtime: break
+			if time = qtime and priority < qpri: break
+		else:
+			i = len(q)
+		q.insert(i, event)
+		return event # The ID
+	#
+	# A variant that specifies the time as a relative time.
+	# This is actually the more commonly used interface.
+	#
+	def enter(self, (delay, priority, action, argument)):
+		time = self.timefunc() + delay
+		return self.enterabs(time, priority, action, argument)
+	#
+	# Remove an event from the queue.
+	# This must be presented the ID as returned by enter().
+	# If the event is not in the queue, this raises RuntimeError.
+	#
+	def cancel(self, event):
+		self.queue.remove(event)
+	#
+	# Check whether the queue is empty.
+	#
+	def empty(self):
+		return len(self.queue) = 0
+	#
+	# Run: execute events until the queue is empty.
+	#
+	# When there is a positive delay until the first event, the
+	# delay function is called and the event is left in the queue;
+	# otherwise, the event is removed from the queue and executed
+	# (its action function is called, passing it the argument).
+	# If the delay function returns prematurely, it is simply
+	# restarted.
+	#
+	# It is legal for both the delay function and the action
+	# function to to modify the queue or to raise an exception;
+	# exceptions are not caught but the scheduler's state
+	# remains well-defined so run() may be called again.
+	#
+	def run(self):
+		q = self.queue
+		while q:
+			time, priority, action, argument = q[0]
+			now = self.timefunc()
+			if now < time:
+				self.delayfunc(time - now)
+			else:
+				del q[0]
+				void = action(argument)
+	#