gevent / gevent / queue.py

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# Copyright (c) 2009-2011 Denis Bilenko. See LICENSE for details.
"""Synchronized queues.

The :mod:`gevent.queue` module implements multi-producer, multi-consumer queues
that work across greenlets, with the API similar to the classes found in the
standard :mod:`Queue` and :class:`multiprocessing <multiprocessing.Queue>` modules.

Changed in version 1.0: Queue(0) now means queue of infinite size, not a channel.

The classes in this module implement iterator protocol. Iterating over queue
means repeatedly calling :meth:`get <Queue.get>` until :meth:`get <Queue.get>` returns ``StopIteration``.

    >>> queue = gevent.queue.Queue()
    >>> queue.put(1)
    >>> queue.put(2)
    >>> queue.put(StopIteration)
    >>> for item in queue:
    ...    print item
    1
    2
"""

import sys
import heapq
import collections

try:
    from Queue import Full, Empty
except ImportError:
    __queue__ = __import__('queue')
    Full = __queue__.Full
    Empty = __queue__.Empty

from gevent.timeout import Timeout
from gevent.hub import get_hub, Waiter, getcurrent


__all__ = ['Queue', 'PriorityQueue', 'LifoQueue', 'JoinableQueue', 'Channel']


class Queue(object):
    """Create a queue object with a given maximum size.

    If *maxsize* is less than zero or ``None``, the queue size is infinite.

    ``Queue(0)`` is a channel, that is, its :meth:`put` method always blocks until the
    item is delivered. (This is unlike the standard :class:`Queue`, where 0 means
    infinite size).
    """

    def __init__(self, maxsize=None):
        if maxsize <= 0:
            self.maxsize = None
            if maxsize == 0:
                import warnings
                warnings.warn('Queue(0) now equivalent to Queue(None); if you want a channel, use Channel',
                              DeprecationWarning, stacklevel=2)
        else:
            self.maxsize = maxsize
        self.getters = set()
        self.putters = set()
        self.hub = get_hub()
        self._event_unlock = self.hub.loop.callback()
        self._init(maxsize)

    # QQQ make maxsize into a property with setter that schedules unlock if necessary

    def _init(self, maxsize):
        self.queue = collections.deque()

    def _get(self):
        return self.queue.popleft()

    def _peek(self):
        return self.queue[0]

    def _put(self, item):
        self.queue.append(item)

    def __repr__(self):
        return '<%s at %s %s>' % (type(self).__name__, hex(id(self)), self._format())

    def __str__(self):
        return '<%s %s>' % (type(self).__name__, self._format())

    def _format(self):
        result = 'maxsize=%r' % (self.maxsize, )
        if getattr(self, 'queue', None):
            result += ' queue=%r' % self.queue
        if self.getters:
            result += ' getters[%s]' % len(self.getters)
        if self.putters:
            result += ' putters[%s]' % len(self.putters)
        return result

    def qsize(self):
        """Return the size of the queue."""
        return len(self.queue)

    def empty(self):
        """Return ``True`` if the queue is empty, ``False`` otherwise."""
        return not self.qsize()

    def full(self):
        """Return ``True`` if the queue is full, ``False`` otherwise.

        ``Queue(None)`` is never full.
        """
        return self.maxsize is not None and self.qsize() >= self.maxsize

    def put(self, item, block=True, timeout=None):
        """Put an item into the queue.

        If optional arg *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 :class:`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 :class:`Full` exception (*timeout*
        is ignored in that case).
        """
        if self.maxsize is None or self.qsize() < self.maxsize:
            # there's a free slot, put an item right away
            self._put(item)
            if self.getters:
                self._schedule_unlock()
        elif self.hub is getcurrent():
            # We're in the mainloop, so we cannot wait; we can switch() to other greenlets though.
            # Check if possible to get a free slot in the queue.
            while self.getters and self.qsize() and self.qsize() >= self.maxsize:
                getter = self.getters.pop()
                getter.switch(getter)
            if self.qsize() < self.maxsize:
                self._put(item)
                return
            raise Full
        elif block:
            waiter = ItemWaiter(item, self)
            self.putters.add(waiter)
            timeout = Timeout.start_new(timeout, Full)
            try:
                if self.getters:
                    self._schedule_unlock()
                result = waiter.get()
                assert result is waiter, "Invalid switch into Queue.put: %r" % (result, )
            finally:
                timeout.cancel()
                self.putters.discard(waiter)
        else:
            raise Full

    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 :class:`Full` exception.
        """
        self.put(item, False)

    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 :class:`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 :class:`Empty` exception
        (*timeout* is ignored in that case).
        """
        if self.qsize():
            if self.putters:
                self._schedule_unlock()
            return self._get()
        elif self.hub is getcurrent():
            # special case to make get_nowait() runnable in the mainloop greenlet
            # there are no items in the queue; try to fix the situation by unlocking putters
            while self.putters:
                self.putters.pop().put_and_switch()
                if self.qsize():
                    return self._get()
            raise Empty
        elif block:
            waiter = Waiter()
            timeout = Timeout.start_new(timeout, Empty)
            try:
                self.getters.add(waiter)
                if self.putters:
                    self._schedule_unlock()
                result = waiter.get()
                assert result is waiter, 'Invalid switch into Queue.get: %r' % (result, )
                return self._get()
            finally:
                self.getters.discard(waiter)
                timeout.cancel()
        else:
            raise Empty

    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 :class:`Empty` exception.
        """
        return self.get(False)

    def peek(self, block=True, timeout=None):
        """Return an item from the queue without removing it.

        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 :class:`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 :class:`Empty` exception
        (*timeout* is ignored in that case).
        """
        if self.qsize():
            return self._peek()
        elif self.hub is getcurrent():
            # special case to make peek(False) runnable in the mainloop greenlet
            # there are no items in the queue; try to fix the situation by unlocking putters
            while self.putters:
                self.putters.pop().put_and_switch()
                if self.qsize():
                    return self._peek()
            raise Empty
        elif block:
            waiter = Waiter()
            timeout = Timeout.start_new(timeout, Empty)
            try:
                self.getters.add(waiter)
                if self.putters:
                    self._schedule_unlock()
                result = waiter.get()
                assert result is waiter, 'Invalid switch into Queue.peek: %r' % (result, )
                return self._peek()
            finally:
                self.getters.discard(waiter)
                timeout.cancel()
        else:
            raise Empty

    def peek_nowait(self):
        return self.peek(False)

    def _unlock(self):
        while True:
            repeat = False
            if self.putters and (self.maxsize is None or self.qsize() < self.maxsize):
                repeat = True
                try:
                    putter = self.putters.pop()
                    self._put(putter.item)
                except:
                    putter.throw(*sys.exc_info())
                else:
                    putter.switch(putter)
            if self.getters and self.qsize():
                repeat = True
                getter = self.getters.pop()
                getter.switch(getter)
            if not repeat:
                return
        # testcase: 2 greenlets: while True: q.put(q.get()) - nothing else has a change to execute
        # to avoid this, schedule unlock with timer(0, ...) once in a while
        # replace 'while True' with 'for _ in xrange(100): ...; self._timer.start(self._unlock)
        # but then I need _timer and self._event_unlock to play with each other

    def _schedule_unlock(self):
        self._event_unlock.start(self._unlock)

    def __iter__(self):
        return self

    def next(self):
        result = self.get()
        if result is StopIteration:
            raise result
        return result


class ItemWaiter(Waiter):
    __slots__ = ['item', 'queue']

    def __init__(self, item, queue):
        Waiter.__init__(self)
        self.item = item
        self.queue = queue

    def put_and_switch(self):
        self.queue._put(self.item)
        self.queue = None
        self.item = None
        return self.switch(self)


class PriorityQueue(Queue):
    '''A subclass of :class:`Queue` that retrieves entries in priority order (lowest first).

    Entries are typically tuples of the form: ``(priority number, data)``.
    '''

    def _init(self, maxsize):
        self.queue = []

    def _put(self, item, heappush=heapq.heappush):
        heappush(self.queue, item)

    def _get(self, heappop=heapq.heappop):
        return heappop(self.queue)


class LifoQueue(Queue):
    '''A subclass of :class:`Queue` that retrieves most recently added entries first.'''

    def _init(self, maxsize):
        self.queue = []

    def _put(self, item):
        self.queue.append(item)

    def _get(self):
        return self.queue.pop()


class JoinableQueue(Queue):
    '''A subclass of :class:`Queue` that additionally has :meth:`task_done` and :meth:`join` methods.'''

    def __init__(self, maxsize=None):
        from gevent.event import Event
        Queue.__init__(self, maxsize)
        self.unfinished_tasks = 0
        self._cond = Event()
        self._cond.set()

    def _format(self):
        result = Queue._format(self)
        if self.unfinished_tasks:
            result += ' tasks=%s _cond=%s' % (self.unfinished_tasks, self._cond)
        return result

    def _put(self, item):
        Queue._put(self, item)
        self.unfinished_tasks += 1
        self._cond.clear()

    def task_done(self):
        '''Indicate that a formerly enqueued task is complete. Used by queue consumer threads.
        For each :meth:`get <Queue.get>` used to fetch a task, a subsequent call to :meth:`task_done` tells the queue
        that the processing on the task is complete.

        If a :meth:`join` is currently blocking, it will resume when all items have been processed
        (meaning that a :meth:`task_done` call was received for every item that had been
        :meth:`put <Queue.put>` into the queue).

        Raises a :exc:`ValueError` if called more times than there were items placed in the queue.
        '''
        if self.unfinished_tasks <= 0:
            raise ValueError('task_done() called too many times')
        self.unfinished_tasks -= 1
        if self.unfinished_tasks == 0:
            self._cond.set()

    def join(self):
        '''Block until all items in the queue have been gotten and processed.

        The count of unfinished tasks goes up whenever an item is added to the queue.
        The count goes down whenever a consumer thread calls :meth:`task_done` to indicate
        that the item was retrieved and all work on it is complete. When the count of
        unfinished tasks drops to zero, :meth:`join` unblocks.
        '''
        self._cond.wait()


class Channel(object):

    def __init__(self):
        self.getters = collections.deque()
        self.putters = collections.deque()
        self.hub = get_hub()
        self._event_unlock = self.hub.loop.callback()

    def __repr__(self):
        return '<%s at %s %s>' % (type(self).__name__, hex(id(self)), self._format())

    def __str__(self):
        return '<%s %s>' % (type(self).__name__, self._format())

    def _format(self):
        result = ''
        if self.getters:
            result += ' getters[%s]' % len(self.getters)
        if self.putters:
            result += ' putters[%s]' % len(self.putters)
        return result

    @property
    def balance(self):
        return len(self.putters) - len(self.getters)

    def qsize(self):
        return 0

    def empty(self):
        return True

    def full(self):
        return True

    def put(self, item, block=True, timeout=None):
        if self.hub is getcurrent():
            if self.getters:
                getter = self.getters.popleft()
                getter.switch(item)
                return
            raise Full

        if not block:
            timeout = 0

        waiter = Waiter()
        item = (item, waiter)
        self.putters.append(item)
        timeout = Timeout.start_new(timeout, Full)
        try:
            if self.getters:
                self._schedule_unlock()
            result = waiter.get()
            assert result is waiter, "Invalid switch into Channel.put: %r" % (result, )
        except:
            self._discard(item)
            raise
        finally:
            timeout.cancel()

    def _discard(self, item):
        try:
            self.putters.remove(item)
        except ValueError:
            pass

    def put_nowait(self, item):
        self.put(item, False)

    def get(self, block=True, timeout=None):
        if self.hub is getcurrent():
            if self.putters:
                item, putter = self.putters.popleft()
                self.hub.loop.run_callback(putter.switch, putter)
                return item

        if not block:
            timeout = 0

        waiter = Waiter()
        timeout = Timeout.start_new(timeout, Empty)
        try:
            self.getters.append(waiter)
            if self.putters:
                self._schedule_unlock()
            return waiter.get()
        except:
            self.getters.remove(waiter)
            raise
        finally:
            timeout.cancel()

    def get_nowait(self):
        return self.get(False)

    def _unlock(self):
        while self.putters and self.getters:
            getter = self.getters.popleft()
            item, putter = self.putters.popleft()
            getter.switch(item)
            putter.switch(putter)

    def _schedule_unlock(self):
        self._event_unlock.start(self._unlock)

    def __iter__(self):
        return self

    def next(self):
        result = self.get()
        if result is StopIteration:
            raise result
        return result
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