from collections import deque, OrderedDict from math import inf import attr from outcome import Error, Value from .abc import SendChannel, ReceiveChannel, Channel from ._util import generic_function, NoPublicConstructor import trio from ._core import enable_ki_protection @generic_function def open_memory_channel(max_buffer_size): """Open a channel for passing objects between tasks within a process. Memory channels are lightweight, cheap to allocate, and entirely in-memory. They don't involve any operating-system resources, or any kind of serialization. They just pass Python objects directly between tasks (with a possible stop in an internal buffer along the way). Channel objects can be closed by calling `~trio.abc.AsyncResource.aclose` or using ``async with``. They are *not* automatically closed when garbage collected. Closing memory channels isn't mandatory, but it is generally a good idea, because it helps avoid situations where tasks get stuck waiting on a channel when there's no-one on the other side. See :ref:`channel-shutdown` for details. Memory channel operations are all atomic with respect to cancellation, either `~trio.abc.ReceiveChannel.receive` will successfully return an object, or it will raise :exc:`Cancelled` while leaving the channel unchanged. Args: max_buffer_size (int or math.inf): The maximum number of items that can be buffered in the channel before :meth:`~trio.abc.SendChannel.send` blocks. Choosing a sensible value here is important to ensure that backpressure is communicated promptly and avoid unnecessary latency; see :ref:`channel-buffering` for more details. If in doubt, use 0. Returns: A pair ``(send_channel, receive_channel)``. If you have trouble remembering which order these go in, remember: data flows from left → right. In addition to the standard channel methods, all memory channel objects provide a ``statistics()`` method, which returns an object with the following fields: * ``current_buffer_used``: The number of items currently stored in the channel buffer. * ``max_buffer_size``: The maximum number of items allowed in the buffer, as passed to :func:`open_memory_channel`. * ``open_send_channels``: The number of open :class:`MemorySendChannel` endpoints pointing to this channel. Initially 1, but can be increased by :meth:`MemorySendChannel.clone`. * ``open_receive_channels``: Likewise, but for open :class:`MemoryReceiveChannel` endpoints. * ``tasks_waiting_send``: The number of tasks blocked in ``send`` on this channel (summing over all clones). * ``tasks_waiting_receive``: The number of tasks blocked in ``receive`` on this channel (summing over all clones). """ if max_buffer_size != inf and not isinstance(max_buffer_size, int): raise TypeError("max_buffer_size must be an integer or math.inf") if max_buffer_size < 0: raise ValueError("max_buffer_size must be >= 0") state = MemoryChannelState(max_buffer_size) return ( MemorySendChannel._create(state), MemoryReceiveChannel._create(state), ) @attr.s(frozen=True, slots=True) class MemoryChannelStats: current_buffer_used = attr.ib() max_buffer_size = attr.ib() open_send_channels = attr.ib() open_receive_channels = attr.ib() tasks_waiting_send = attr.ib() tasks_waiting_receive = attr.ib() @attr.s(slots=True) class MemoryChannelState: max_buffer_size = attr.ib() data = attr.ib(factory=deque) # Counts of open endpoints using this state open_send_channels = attr.ib(default=0) open_receive_channels = attr.ib(default=0) # {task: value} send_tasks = attr.ib(factory=OrderedDict) # {task: None} receive_tasks = attr.ib(factory=OrderedDict) def statistics(self): return MemoryChannelStats( current_buffer_used=len(self.data), max_buffer_size=self.max_buffer_size, open_send_channels=self.open_send_channels, open_receive_channels=self.open_receive_channels, tasks_waiting_send=len(self.send_tasks), tasks_waiting_receive=len(self.receive_tasks), ) @attr.s(eq=False, repr=False) class MemorySendChannel(SendChannel, metaclass=NoPublicConstructor): _state = attr.ib() _closed = attr.ib(default=False) # This is just the tasks waiting on *this* object. As compared to # self._state.send_tasks, which includes tasks from this object and # all clones. _tasks = attr.ib(factory=set) def __attrs_post_init__(self): self._state.open_send_channels += 1 def __repr__(self): return "".format( id(self), id(self._state) ) def statistics(self): # XX should we also report statistics specific to this object? return self._state.statistics() @enable_ki_protection def send_nowait(self, value): """Like `~trio.abc.SendChannel.send`, but if the channel's buffer is full, raises `WouldBlock` instead of blocking. """ if self._closed: raise trio.ClosedResourceError if self._state.open_receive_channels == 0: raise trio.BrokenResourceError if self._state.receive_tasks: assert not self._state.data task, _ = self._state.receive_tasks.popitem(last=False) task.custom_sleep_data._tasks.remove(task) trio.lowlevel.reschedule(task, Value(value)) elif len(self._state.data) < self._state.max_buffer_size: self._state.data.append(value) else: raise trio.WouldBlock @enable_ki_protection async def send(self, value): """See `SendChannel.send `. Memory channels allow multiple tasks to call `send` at the same time. """ await trio.lowlevel.checkpoint_if_cancelled() try: self.send_nowait(value) except trio.WouldBlock: pass else: await trio.lowlevel.cancel_shielded_checkpoint() return task = trio.lowlevel.current_task() self._tasks.add(task) self._state.send_tasks[task] = value task.custom_sleep_data = self def abort_fn(_): self._tasks.remove(task) del self._state.send_tasks[task] return trio.lowlevel.Abort.SUCCEEDED await trio.lowlevel.wait_task_rescheduled(abort_fn) @enable_ki_protection def clone(self): """Clone this send channel object. This returns a new `MemorySendChannel` object, which acts as a duplicate of the original: sending on the new object does exactly the same thing as sending on the old object. (If you're familiar with `os.dup`, then this is a similar idea.) However, closing one of the objects does not close the other, and receivers don't get `EndOfChannel` until *all* clones have been closed. This is useful for communication patterns that involve multiple producers all sending objects to the same destination. If you give each producer its own clone of the `MemorySendChannel`, and then make sure to close each `MemorySendChannel` when it's finished, receivers will automatically get notified when all producers are finished. See :ref:`channel-mpmc` for examples. Raises: trio.ClosedResourceError: if you already closed this `MemorySendChannel` object. """ if self._closed: raise trio.ClosedResourceError return MemorySendChannel._create(self._state) def __enter__(self): return self def __exit__(self, exc_type, exc_val, exc_tb): self.close() @enable_ki_protection def close(self): """Close this send channel object synchronously. All channel objects have an asynchronous `~.AsyncResource.aclose` method. Memory channels can also be closed synchronously. This has the same effect on the channel and other tasks using it, but `close` is not a trio checkpoint. This simplifies cleaning up in cancelled tasks. Using ``with send_channel:`` will close the channel object on leaving the with block. """ if self._closed: return self._closed = True for task in self._tasks: trio.lowlevel.reschedule(task, Error(trio.ClosedResourceError())) del self._state.send_tasks[task] self._tasks.clear() self._state.open_send_channels -= 1 if self._state.open_send_channels == 0: assert not self._state.send_tasks for task in self._state.receive_tasks: task.custom_sleep_data._tasks.remove(task) trio.lowlevel.reschedule(task, Error(trio.EndOfChannel())) self._state.receive_tasks.clear() @enable_ki_protection async def aclose(self): self.close() await trio.lowlevel.checkpoint() @attr.s(eq=False, repr=False) class MemoryReceiveChannel(ReceiveChannel, metaclass=NoPublicConstructor): _state = attr.ib() _closed = attr.ib(default=False) _tasks = attr.ib(factory=set) def __attrs_post_init__(self): self._state.open_receive_channels += 1 def statistics(self): return self._state.statistics() def __repr__(self): return "".format( id(self), id(self._state) ) @enable_ki_protection def receive_nowait(self): """Like `~trio.abc.ReceiveChannel.receive`, but if there's nothing ready to receive, raises `WouldBlock` instead of blocking. """ if self._closed: raise trio.ClosedResourceError if self._state.send_tasks: task, value = self._state.send_tasks.popitem(last=False) task.custom_sleep_data._tasks.remove(task) trio.lowlevel.reschedule(task) self._state.data.append(value) # Fall through if self._state.data: return self._state.data.popleft() if not self._state.open_send_channels: raise trio.EndOfChannel raise trio.WouldBlock @enable_ki_protection async def receive(self): """See `ReceiveChannel.receive `. Memory channels allow multiple tasks to call `receive` at the same time. The first task will get the first item sent, the second task will get the second item sent, and so on. """ await trio.lowlevel.checkpoint_if_cancelled() try: value = self.receive_nowait() except trio.WouldBlock: pass else: await trio.lowlevel.cancel_shielded_checkpoint() return value task = trio.lowlevel.current_task() self._tasks.add(task) self._state.receive_tasks[task] = None task.custom_sleep_data = self def abort_fn(_): self._tasks.remove(task) del self._state.receive_tasks[task] return trio.lowlevel.Abort.SUCCEEDED return await trio.lowlevel.wait_task_rescheduled(abort_fn) @enable_ki_protection def clone(self): """Clone this receive channel object. This returns a new `MemoryReceiveChannel` object, which acts as a duplicate of the original: receiving on the new object does exactly the same thing as receiving on the old object. However, closing one of the objects does not close the other, and the underlying channel is not closed until all clones are closed. (If you're familiar with `os.dup`, then this is a similar idea.) This is useful for communication patterns that involve multiple consumers all receiving objects from the same underlying channel. See :ref:`channel-mpmc` for examples. .. warning:: The clones all share the same underlying channel. Whenever a clone :meth:`receive`\\s a value, it is removed from the channel and the other clones do *not* receive that value. If you want to send multiple copies of the same stream of values to multiple destinations, like :func:`itertools.tee`, then you need to find some other solution; this method does *not* do that. Raises: trio.ClosedResourceError: if you already closed this `MemoryReceiveChannel` object. """ if self._closed: raise trio.ClosedResourceError return MemoryReceiveChannel._create(self._state) def __enter__(self): return self def __exit__(self, exc_type, exc_val, exc_tb): self.close() @enable_ki_protection def close(self): """Close this receive channel object synchronously. All channel objects have an asynchronous `~.AsyncResource.aclose` method. Memory channels can also be closed synchronously. This has the same effect on the channel and other tasks using it, but `close` is not a trio checkpoint. This simplifies cleaning up in cancelled tasks. Using ``with receive_channel:`` will close the channel object on leaving the with block. """ if self._closed: return self._closed = True for task in self._tasks: trio.lowlevel.reschedule(task, Error(trio.ClosedResourceError())) del self._state.receive_tasks[task] self._tasks.clear() self._state.open_receive_channels -= 1 if self._state.open_receive_channels == 0: assert not self._state.receive_tasks for task in self._state.send_tasks: task.custom_sleep_data._tasks.remove(task) trio.lowlevel.reschedule(task, Error(trio.BrokenResourceError())) self._state.send_tasks.clear() self._state.data.clear() @enable_ki_protection async def aclose(self): self.close() await trio.lowlevel.checkpoint()