# Copyright 2019, David Wilson
#
# Redistribution and use in source and binary forms, with or without
# modification, are permitted provided that the following conditions are met:
#
# 1. Redistributions of source code must retain the above copyright notice,
# this list of conditions and the following disclaimer.
#
# 2. Redistributions in binary form must reproduce the above copyright notice,
# this list of conditions and the following disclaimer in the documentation
# and/or other materials provided with the distribution.
#
# 3. Neither the name of the copyright holder nor the names of its contributors
# may be used to endorse or promote products derived from this software without
# specific prior written permission.
#
# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
# AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
# IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
# ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
# LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
# CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
# SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
# INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
# CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
# ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
# POSSIBILITY OF SUCH DAMAGE.
# !mitogen: minify_safe
import mitogen.core
class Error(mitogen.core.Error):
pass
class Event(object):
"""
Represents one selected event.
"""
#: The first Receiver or Latch the event traversed.
source = None
#: The :class:`mitogen.core.Message` delivered to a receiver, or the object
#: posted to a latch.
data = None
class Select(object):
"""
Support scatter/gather asynchronous calls and waiting on multiple
:class:`receivers <mitogen.core.Receiver>`,
:class:`channels <mitogen.core.Channel>`,
:class:`latches <mitogen.core.Latch>`, and
:class:`sub-selects <Select>`.
If `oneshot` is :data:`True`, then remove each receiver as it yields a
result; since :meth:`__iter__` terminates once the final receiver is
removed, this makes it convenient to respond to calls made in parallel::
total = 0
recvs = [c.call_async(long_running_operation) for c in contexts]
for msg in mitogen.select.Select(recvs):
print('Got %s from %s' % (msg, msg.receiver))
total += msg.unpickle()
# Iteration ends when last Receiver yields a result.
print('Received total %s from %s receivers' % (total, len(recvs)))
:class:`Select` may drive a long-running scheduler:
.. code-block:: python
with mitogen.select.Select(oneshot=False) as select:
while running():
for msg in select:
process_result(msg.receiver.context, msg.unpickle())
for context, workfunc in get_new_work():
select.add(context.call_async(workfunc))
:class:`Select` may be nested:
.. code-block:: python
subselects = [
mitogen.select.Select(get_some_work()),
mitogen.select.Select(get_some_work()),
mitogen.select.Select([
mitogen.select.Select(get_some_work()),
mitogen.select.Select(get_some_work())
])
]
for msg in mitogen.select.Select(selects):
print(msg.unpickle())
:class:`Select` may be used to mix inter-thread and inter-process IO::
latch = mitogen.core.Latch()
start_thread(latch)
recv = remote_host.call_async(os.getuid)
sel = Select([latch, recv])
event = sel.get_event()
if event.source is latch:
# woken by a local thread
else:
# woken by function call result
"""
notify = None
def __init__(self, receivers=(), oneshot=True):
self._receivers = []
self._oneshot = oneshot
self._latch = mitogen.core.Latch()
for recv in receivers:
self.add(recv)
@classmethod
def all(cls, receivers):
"""
Take an iterable of receivers and retrieve a :class:`Message
<mitogen.core.Message>` from each, returning the result of calling
:meth:`Message.unpickle() <mitogen.core.Message.unpickle>` on each in
turn. Results are returned in the order they arrived.
This is sugar for handling batch :meth:`Context.call_async
<mitogen.parent.Context.call_async>` invocations:
.. code-block:: python
print('Total disk usage: %.02fMiB' % (sum(
mitogen.select.Select.all(
context.call_async(get_disk_usage)
for context in contexts
) / 1048576.0
),))
However, unlike in a naive comprehension such as:
.. code-block:: python
recvs = [c.call_async(get_disk_usage) for c in contexts]
sum(recv.get().unpickle() for recv in recvs)
Result processing happens in the order results arrive, rather than the
order requests were issued, so :meth:`all` should always be faster.
"""
return list(msg.unpickle() for msg in cls(receivers))
def _put(self, value):
self._latch.put(value)
if self.notify:
self.notify(self)
def __bool__(self):
"""
Return :data:`True` if any receivers are registered with this select.
"""
return bool(self._receivers)
__nonzero__ = __bool__
def __enter__(self):
return self
def __exit__(self, e_type, e_val, e_tb):
self.close()
def iter_data(self):
"""
Yield :attr:`Event.data` until no receivers remain in the select,
either because `oneshot` is :data:`True`, or each receiver was
explicitly removed via :meth:`remove`.
:meth:`__iter__` is an alias for :meth:`iter_data`, allowing loops
like::
for msg in Select([recv1, recv2]):
print msg.unpickle()
"""
while self._receivers:
yield self.get_event().data
__iter__ = iter_data
def iter_events(self):
"""
Yield :class:`Event` instances until no receivers remain in the select.
"""
while self._receivers:
yield self.get_event()
loop_msg = 'Adding this Select instance would create a Select cycle'
def _check_no_loop(self, recv):
if recv is self:
raise Error(self.loop_msg)
for recv_ in self._receivers:
if recv_ == recv:
raise Error(self.loop_msg)
if isinstance(recv_, Select):
recv_._check_no_loop(recv)
owned_msg = 'Cannot add: Receiver is already owned by another Select'
def add(self, recv):
"""
Add a :class:`mitogen.core.Receiver`, :class:`Select` or
:class:`mitogen.core.Latch` to the select.
:raises mitogen.select.Error:
An attempt was made to add a :class:`Select` to which this select
is indirectly a member of.
"""
if isinstance(recv, Select):
recv._check_no_loop(self)
self._receivers.append(recv)
if recv.notify is not None:
raise Error(self.owned_msg)
recv.notify = self._put
# After installing the notify function, _put() will potentially begin
# receiving calls from other threads immediately, but not for items
# they already had buffered. For those we call _put(), possibly
# duplicating the effect of other _put() being made concurrently, such
# that the Select ends up with more items in its buffer than exist in
# the underlying receivers. We handle the possibility of receivers
# marked notified yet empty inside Select.get(), so this should be
# robust.
for _ in range(recv.size()):
self._put(recv)
not_present_msg = 'Instance is not a member of this Select'
def remove(self, recv):
"""
Remove an object from from the select. Note that if the receiver has
notified prior to :meth:`remove`, it will still be returned by a
subsequent :meth:`get`. This may change in a future version.
"""
try:
if recv.notify != self._put:
raise ValueError
self._receivers.remove(recv)
recv.notify = None
except (IndexError, ValueError):
raise Error(self.not_present_msg)
def close(self):
"""
Remove the select's notifier function from each registered receiver,
mark the associated latch as closed, and cause any thread currently
sleeping in :meth:`get` to be woken with
:class:`mitogen.core.LatchError`.
This is necessary to prevent memory leaks in long-running receivers. It
is called automatically when the Python :keyword:`with` statement is
used.
"""
for recv in self._receivers[:]:
self.remove(recv)
self._latch.close()
def size(self):
"""
Return the number of items currently buffered.
As with :class:`Queue.Queue`, `0` may be returned even though a
subsequent call to :meth:`get` will succeed, since a message may be
posted at any moment between :meth:`size` and :meth:`get`.
As with :class:`Queue.Queue`, `>0` may be returned even though a
subsequent call to :meth:`get` will block, since another waiting thread
may be woken at any moment between :meth:`size` and :meth:`get`.
"""
return sum(recv.size() for recv in self._receivers)
def empty(self):
"""
Return `size() == 0`.
.. deprecated:: 0.2.8
Use :meth:`size` instead.
"""
return self._latch.empty()
empty_msg = 'Cannot get(), Select instance is empty'
def get(self, timeout=None, block=True):
"""
Call `get_event(timeout, block)` returning :attr:`Event.data` of the
first available event.
"""
return self.get_event(timeout, block).data
def get_event(self, timeout=None, block=True):
"""
Fetch the next available :class:`Event` from any source, or raise
:class:`mitogen.core.TimeoutError` if no value is available within
`timeout` seconds.
On success, the message's :attr:`receiver
<mitogen.core.Message.receiver>` attribute is set to the receiver.
:param float timeout:
Timeout in seconds.
:param bool block:
If :data:`False`, immediately raise
:class:`mitogen.core.TimeoutError` if the select is empty.
:return:
:class:`Event`.
:raises mitogen.core.TimeoutError:
Timeout was reached.
:raises mitogen.core.LatchError:
:meth:`close` has been called, and the underlying latch is no
longer valid.
"""
if not self._receivers:
raise Error(self.empty_msg)
while True:
recv = self._latch.get(timeout=timeout, block=block)
try:
if isinstance(recv, Select):
event = recv.get_event(block=False)
else:
event = Event()
event.source = recv
event.data = recv.get(block=False)
if self._oneshot:
self.remove(recv)
if isinstance(recv, mitogen.core.Receiver):
# Remove in 0.3.x.
event.data.receiver = recv
return event
except mitogen.core.TimeoutError:
# A receiver may have been queued with no result if another
# thread drained it before we woke up, or because another
# thread drained it between add() calling recv.empty() and
# self._put(), or because Select.add() caused duplicate _put()
# calls. In this case simply retry.
continue