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"""A multi-producer, multi-consumer queue."""
from time import time as _time
from collections import deque
__all__ = ['Empty', 'Full', 'Queue']
class Empty(Exception):
"Exception raised by Queue.get(block=0)/get_nowait()."
pass
class Full(Exception):
"Exception raised by Queue.put(block=0)/put_nowait()."
pass
class Queue:
def __init__(self, maxsize=0):
"""Initialize a queue object with a given maximum size.
If maxsize is <= 0, the queue size is infinite.
"""
try:
import threading
except ImportError:
import dummy_threading as threading
self._init(maxsize)
# mutex must be held whenever the queue is mutating. All methods
# that acquire mutex must release it before returning. mutex
# is shared between the two conditions, so acquiring and
# releasing the conditions also acquires and releases mutex.
self.mutex = threading.Lock()
# Notify not_empty whenever an item is added to the queue; a
# thread waiting to get is notified then.
self.not_empty = threading.Condition(self.mutex)
# Notify not_full whenever an item is removed from the queue;
# a thread waiting to put is notified then.
self.not_full = threading.Condition(self.mutex)
def qsize(self):
"""Return the approximate size of the queue (not reliable!)."""
self.mutex.acquire()
n = self._qsize()
self.mutex.release()
return n
def empty(self):
"""Return True if the queue is empty, False otherwise (not reliable!)."""
self.mutex.acquire()
n = self._empty()
self.mutex.release()
return n
def full(self):
"""Return True if the queue is full, False otherwise (not reliable!)."""
self.mutex.acquire()
n = self._full()
self.mutex.release()
return n
def put(self, item, block=True, timeout=None):
"""Put an item into the queue.
If optional args 'block' is true and 'timeout' is None (the default),
block if necessary until a free slot is available. If 'timeout' is
a positive number, it blocks at most 'timeout' seconds and raises
the Full exception if no free slot was available within that time.
Otherwise ('block' is false), put an item on the queue if a free slot
is immediately available, else raise the Full exception ('timeout'
is ignored in that case).
"""
if not block:
return self.put_nowait(item)
self.not_full.acquire()
try:
if timeout is None:
while self._full():
self.not_full.wait()
else:
if timeout < 0:
raise ValueError("'timeout' must be a positive number")
endtime = _time() + timeout
while self._full():
remaining = endtime - _time()
if remaining < 0.0:
raise Full
self.not_full.wait(remaining)
self._put(item)
self.not_empty.notify()
finally:
self.not_full.release()
def put_nowait(self, item):
"""Put an item into the queue without blocking.
Only enqueue the item if a free slot is immediately available.
Otherwise raise the Full exception.
"""
self.not_full.acquire()
try:
if self._full():
raise Full
else:
self._put(item)
self.not_empty.notify()
finally:
self.not_full.release()
def get(self, block=True, timeout=None):
"""Remove and return an item from the queue.
If optional args 'block' is true and 'timeout' is None (the default),
block if necessary until an item is available. If 'timeout' is
a positive number, it blocks at most 'timeout' seconds and raises
the Empty exception if no item was available within that time.
Otherwise ('block' is false), return an item if one is immediately
available, else raise the Empty exception ('timeout' is ignored
in that case).
"""
if not block:
return self.get_nowait()
self.not_empty.acquire()
try:
if timeout is None:
while self._empty():
self.not_empty.wait()
else:
if timeout < 0:
raise ValueError("'timeout' must be a positive number")
endtime = _time() + timeout
while self._empty():
remaining = endtime - _time()
if remaining < 0.0:
raise Empty
self.not_empty.wait(remaining)
item = self._get()
self.not_full.notify()
return item
finally:
self.not_empty.release()
def get_nowait(self):
"""Remove and return an item from the queue without blocking.
Only get an item if one is immediately available. Otherwise
raise the Empty exception.
"""
self.not_empty.acquire()
try:
if self._empty():
raise Empty
else:
item = self._get()
self.not_full.notify()
return item
finally:
self.not_empty.release()
# 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 = deque()
def _qsize(self):
return len(self.queue)
# Check whether 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):
return self.queue.popleft()
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