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mitogen-0.3.9/mitogen/select.py
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348
mitogen-0.3.9/mitogen/select.py
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# Copyright 2019, 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 Event(object):
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"""
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Represents one selected event.
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"""
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#: The first Receiver or Latch the event traversed.
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source = None
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#: The :class:`mitogen.core.Message` delivered to a receiver, or the object
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#: posted to a latch.
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data = None
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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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:class:`receivers <mitogen.core.Receiver>`,
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:class:`channels <mitogen.core.Channel>`,
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:class:`latches <mitogen.core.Latch>`, and
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:class:`sub-selects <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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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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:class:`Select` may be used to mix inter-thread and inter-process IO::
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latch = mitogen.core.Latch()
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start_thread(latch)
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recv = remote_host.call_async(os.getuid)
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sel = Select([latch, recv])
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event = sel.get_event()
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if event.source is latch:
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# woken by a local thread
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else:
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# woken by function call result
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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
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<mitogen.core.Message>` from each, returning the result of calling
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:meth:`Message.unpickle() <mitogen.core.Message.unpickle>` on each in
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turn. 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_data(self):
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"""
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Yield :attr:`Event.data` until no receivers remain in the select,
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either because `oneshot` is :data:`True`, or each receiver was
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explicitly removed via :meth:`remove`.
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:meth:`__iter__` is an alias for :meth:`iter_data`, allowing loops
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like::
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for msg in Select([recv1, recv2]):
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print msg.unpickle()
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"""
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while self._receivers:
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yield self.get_event().data
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__iter__ = iter_data
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def iter_events(self):
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"""
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Yield :class:`Event` instances until no receivers remain in the select.
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"""
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while self._receivers:
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yield self.get_event()
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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 a :class:`mitogen.core.Receiver`, :class:`Select` or
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:class:`mitogen.core.Latch` to the 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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# After installing the notify function, _put() will potentially begin
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# receiving calls from other threads immediately, but not for items
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# they already had buffered. For those we call _put(), possibly
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# duplicating the effect of other _put() being made concurrently, such
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# that the Select ends up with more items in its buffer than exist in
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# the underlying receivers. We handle the possibility of receivers
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# marked notified yet empty inside Select.get(), so this should be
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# robust.
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for _ in range(recv.size()):
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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 an object from from the select. Note that if the receiver has
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notified prior to :meth:`remove`, it will still be returned by a
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subsequent :meth:`get`. 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 size(self):
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"""
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Return the number of items currently buffered.
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As with :class:`Queue.Queue`, `0` may be returned even though a
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subsequent call to :meth:`get` will succeed, since a message may be
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posted at any moment between :meth:`size` and :meth:`get`.
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As with :class:`Queue.Queue`, `>0` may be returned even though a
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subsequent call to :meth:`get` will block, since another waiting thread
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may be woken at any moment between :meth:`size` and :meth:`get`.
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"""
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return sum(recv.size() for recv in self._receivers)
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def empty(self):
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"""
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Return `size() == 0`.
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.. deprecated:: 0.2.8
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Use :meth:`size` instead.
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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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Call `get_event(timeout, block)` returning :attr:`Event.data` of the
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first available event.
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"""
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return self.get_event(timeout, block).data
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def get_event(self, timeout=None, block=True):
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"""
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Fetch the next available :class:`Event` from any source, 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:`Event`.
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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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if isinstance(recv, Select):
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event = recv.get_event(block=False)
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else:
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event = Event()
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event.source = recv
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event.data = recv.get(block=False)
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if self._oneshot:
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self.remove(recv)
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if isinstance(recv, mitogen.core.Receiver):
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# Remove in 0.3.x.
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event.data.receiver = recv
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return event
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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(), or because Select.add() caused duplicate _put()
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# calls. In this case simply retry.
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continue
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