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280 lines
9.8 KiB
Python
280 lines
9.8 KiB
Python
# Copyright 2017, David Wilson
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#
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# Redistribution and use in source and binary forms, with or without
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# modification, are permitted provided that the following conditions are met:
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#
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# 1. Redistributions of source code must retain the above copyright notice,
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# this list of conditions and the following disclaimer.
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#
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# 2. Redistributions in binary form must reproduce the above copyright notice,
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# this list of conditions and the following disclaimer in the documentation
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# and/or other materials provided with the distribution.
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#
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# 3. Neither the name of the copyright holder nor the names of its contributors
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# may be used to endorse or promote products derived from this software without
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# specific prior written permission.
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#
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# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
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# AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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# IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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# ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
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# LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
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# CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
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# SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
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# INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
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# CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
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# ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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# POSSIBILITY OF SUCH DAMAGE.
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# !mitogen: minify_safe
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import mitogen.core
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class Error(mitogen.core.Error):
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pass
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class Select(object):
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"""
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Support scatter/gather asynchronous calls and waiting on multiple
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receivers, channels, and sub-Selects. Accepts a sequence of
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:class:`mitogen.core.Receiver` or :class:`mitogen.select.Select` instances
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and returns the first value posted to any receiver or select.
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If `oneshot` is :data:`True`, then remove each receiver as it yields a
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result; since :meth:`__iter__` terminates once the final receiver is
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removed, this makes it convenient to respond to calls made in parallel:
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.. code-block:: python
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total = 0
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recvs = [c.call_async(long_running_operation) for c in contexts]
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for msg in mitogen.select.Select(recvs):
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print('Got %s from %s' % (msg, msg.receiver))
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total += msg.unpickle()
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# Iteration ends when last Receiver yields a result.
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print('Received total %s from %s receivers' % (total, len(recvs)))
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:class:`Select` may drive a long-running scheduler:
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.. code-block:: python
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with mitogen.select.Select(oneshot=False) as select:
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while running():
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for msg in select:
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process_result(msg.receiver.context, msg.unpickle())
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for context, workfunc in get_new_work():
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select.add(context.call_async(workfunc))
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:class:`Select` may be nested:
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.. code-block:: python
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subselects = [
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mitogen.select.Select(get_some_work()),
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mitogen.select.Select(get_some_work()),
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mitogen.select.Select([
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mitogen.select.Select(get_some_work()),
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mitogen.select.Select(get_some_work())
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])
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]
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for msg in mitogen.select.Select(selects):
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print(msg.unpickle())
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"""
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notify = None
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def __init__(self, receivers=(), oneshot=True):
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self._receivers = []
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self._oneshot = oneshot
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self._latch = mitogen.core.Latch()
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for recv in receivers:
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self.add(recv)
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@classmethod
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def all(cls, receivers):
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"""
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Take an iterable of receivers and retrieve a :class:`Message` from
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each, returning the result of calling `msg.unpickle()` on each in turn.
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Results are returned in the order they arrived.
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This is sugar for handling batch :meth:`Context.call_async
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<mitogen.parent.Context.call_async>` invocations:
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.. code-block:: python
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print('Total disk usage: %.02fMiB' % (sum(
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mitogen.select.Select.all(
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context.call_async(get_disk_usage)
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for context in contexts
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) / 1048576.0
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),))
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However, unlike in a naive comprehension such as:
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.. code-block:: python
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recvs = [c.call_async(get_disk_usage) for c in contexts]
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sum(recv.get().unpickle() for recv in recvs)
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Result processing happens in the order results arrive, rather than the
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order requests were issued, so :meth:`all` should always be faster.
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"""
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return list(msg.unpickle() for msg in cls(receivers))
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def _put(self, value):
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self._latch.put(value)
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if self.notify:
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self.notify(self)
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def __bool__(self):
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"""
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Return :data:`True` if any receivers are registered with this select.
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"""
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return bool(self._receivers)
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__nonzero__ = __bool__
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def __enter__(self):
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return self
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def __exit__(self, e_type, e_val, e_tb):
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self.close()
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def __iter__(self):
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"""
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Yield the result of :meth:`get` until no receivers remain in the
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select, either because `oneshot` is :data:`True`, or each receiver was
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explicitly removed via :meth:`remove`.
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"""
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while self._receivers:
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yield self.get()
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loop_msg = 'Adding this Select instance would create a Select cycle'
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def _check_no_loop(self, recv):
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if recv is self:
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raise Error(self.loop_msg)
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for recv_ in self._receivers:
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if recv_ == recv:
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raise Error(self.loop_msg)
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if isinstance(recv_, Select):
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recv_._check_no_loop(recv)
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owned_msg = 'Cannot add: Receiver is already owned by another Select'
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def add(self, recv):
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"""
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Add the :class:`mitogen.core.Receiver` or :class:`Select` `recv` to the
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select.
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:raises mitogen.select.Error:
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An attempt was made to add a :class:`Select` to which this select
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is indirectly a member of.
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"""
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if isinstance(recv, Select):
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recv._check_no_loop(self)
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self._receivers.append(recv)
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if recv.notify is not None:
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raise Error(self.owned_msg)
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recv.notify = self._put
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# Avoid race by polling once after installation.
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if not recv.empty():
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self._put(recv)
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not_present_msg = 'Instance is not a member of this Select'
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def remove(self, recv):
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"""
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Remove the :class:`mitogen.core.Receiver` or :class:`Select` `recv`
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from the select. Note that if the receiver has notified prior to
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:meth:`remove`, it will still be returned by a subsequent :meth:`get`.
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This may change in a future version.
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"""
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try:
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if recv.notify != self._put:
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raise ValueError
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self._receivers.remove(recv)
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recv.notify = None
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except (IndexError, ValueError):
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raise Error(self.not_present_msg)
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def close(self):
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"""
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Remove the select's notifier function from each registered receiver,
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mark the associated latch as closed, and cause any thread currently
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sleeping in :meth:`get` to be woken with
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:class:`mitogen.core.LatchError`.
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This is necessary to prevent memory leaks in long-running receivers. It
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is called automatically when the Python :keyword:`with` statement is
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used.
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"""
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for recv in self._receivers[:]:
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self.remove(recv)
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self._latch.close()
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def empty(self):
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"""
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Return :data:`True` if calling :meth:`get` would block.
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As with :class:`Queue.Queue`, :data:`True` may be returned even though
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a subsequent call to :meth:`get` will succeed, since a message may be
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posted at any moment between :meth:`empty` and :meth:`get`.
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:meth:`empty` may return :data:`False` even when :meth:`get` would
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block if another thread has drained a receiver added to this select.
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This can be avoided by only consuming each receiver from a single
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thread.
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"""
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return self._latch.empty()
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empty_msg = 'Cannot get(), Select instance is empty'
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def get(self, timeout=None, block=True):
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"""
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Fetch the next available value from any receiver, or raise
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:class:`mitogen.core.TimeoutError` if no value is available within
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`timeout` seconds.
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On success, the message's :attr:`receiver
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<mitogen.core.Message.receiver>` attribute is set to the receiver.
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:param float timeout:
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Timeout in seconds.
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:param bool block:
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If :data:`False`, immediately raise
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:class:`mitogen.core.TimeoutError` if the select is empty.
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:return:
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:class:`mitogen.core.Message`
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:raises mitogen.core.TimeoutError:
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Timeout was reached.
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:raises mitogen.core.LatchError:
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:meth:`close` has been called, and the underlying latch is no
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longer valid.
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"""
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if not self._receivers:
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raise Error(self.empty_msg)
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while True:
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recv = self._latch.get(timeout=timeout, block=block)
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try:
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msg = recv.get(block=False)
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if self._oneshot:
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self.remove(recv)
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msg.receiver = recv
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return msg
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except mitogen.core.TimeoutError:
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# A receiver may have been queued with no result if another
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# thread drained it before we woke up, or because another
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# thread drained it between add() calling recv.empty() and
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# self._put(). In this case just sleep again.
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continue
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