New module implementing a multi-everything queue.

Author: gvanrossum

Lib/Queue.py

@@ -0,0 +1,122 @@
+# A multi-producer, multi-consumer queue.
+
+Empty = 'Queue.Empty' # Exception raised by get_nowait()
+
+class Queue:
+
+	# Initialize a queue object with a given maximum size
+	# (If maxsize is <= 0, the maximum size is infinite)
+	def init(self, maxsize):
+		import thread
+		self._init(maxsize)
+		self.mutex = thread.allocate_lock()
+		self.esema = thread.allocate_lock()
+		self.esema.acquire_lock()
+		self.fsema = thread.allocate_lock()
+		return self
+
+	# Get an approximation of the queue size (not reliable!)
+	def qsize(self):
+		self.mutex.acquire_lock()
+		n = self._qsize()
+		self.mutex.release_lock()
+		return n
+
+	# Check if the queue is empty (not reliable!)
+	def empty(self):
+		self.mutex.acquire_lock()
+		n = self._empty()
+		self.mutex.release_lock()
+		return n
+
+	# Check if the queue is full (not reliable!)
+	def full(self):
+		self.mutex.acquire_lock()
+		n = self._full()
+		self.mutex.release_lock()
+		return n
+
+	# Put a new item into the queue
+	def put(self, item):
+		self.fsema.acquire_lock()
+		self.mutex.acquire_lock()
+		was_empty = self._empty()
+		self._put(item)
+		if was_empty:
+			self.esema.release_lock()
+		if not self._full():
+			self.fsema.release_lock()
+		self.mutex.release_lock()
+
+	# Get an item from the queue,
+	# blocking if necessary until one is available
+	def get(self):
+		self.esema.acquire_lock()
+		self.mutex.acquire_lock()
+		was_full = self._full()
+		item = self._get()
+		if was_full:
+			self.fsema.release_lock()
+		if not self._empty():
+			self.esema.release_lock()
+		self.mutex.release_lock()
+		return item
+
+	# Get an item from the queue if one is immediately available,
+	# raise Empty if the queue is empty or temporarily unavailable
+	def get_nowait(self):
+		locked = self.esema.acquire_lock(0)
+		self.mutex.acquire_lock()
+		if self._empty():
+			# The queue is empyt -- we can't have esema
+			self.mutex.release_lock()
+			raise Empty
+		if not locked:
+			locked = self.esema.acquire_lock(0)
+			if not locked:
+				# Somebody else has esema
+				# but we have mutex --
+				# go out of their way
+				self.mutex.release_lock()
+				raise Empty
+		was_full = self._full()
+		item = self._get()
+		if was_full:
+			self.fsema.release_lock()
+		if not self._empty():
+			self.esema.release_lock()
+		self.mutex.release_lock()
+		return item
+
+	# XXX Need to define put_nowait() as well.
+		
+
+	# Override these methods to implement other queue organizations
+	# (e.g. stack or priority queue).
+	# These will only be called with appropriate locks held
+
+	# Initialize the queue representation
+	def _init(self, maxsize):
+		self.maxsize = maxsize
+		self.queue = []
+
+	def _qsize(self):
+		return len(self.queue)
+
+	# Check wheter the queue is empty
+	def _empty(self):
+		return not self.queue
+
+	# Check whether the queue is full
+	def _full(self):
+		return self.maxsize > 0 and len(self.queue) == self.maxsize
+
+	# Put a new item in the queue
+	def _put(self, item):
+		self.queue.append(item)
+
+	# Get an item from the queue
+	def _get(self):
+		item = self.queue[0]
+		del self.queue[0]
+		return item