495 lines
13 KiB
Python
495 lines
13 KiB
Python
# Task synchronization primitives
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import structio
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from structio.core.syscalls import suspend, checkpoint
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from structio.exceptions import ResourceClosed, WouldBlock
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from structio.core.run import current_task, current_loop
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from structio.abc import ReadableChannel, WritableChannel, Channel
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from structio.util.ki import enable_ki_protection
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from structio.util.misc import ThereCanBeOnlyOne
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from structio.core.task import Task
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from collections import deque, defaultdict
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from typing import Any, Callable, Coroutine
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from functools import partial, wraps
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from heapq import heappush, heappop
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class Event:
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"""
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A wrapper around a boolean value that can be waited
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on asynchronously. The majority of structio's API is
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designed on top of/around this class, as it constitutes
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the simplest synchronization primitive there is
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"""
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def __init__(self):
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self._set = False
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self._tasks: deque[Task] = deque()
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def is_set(self):
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return self._set
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@enable_ki_protection
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async def wait(self):
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"""
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Wait until someone else calls set() on
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this event. If the event has already been
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set, this method returns immediately
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"""
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if self.is_set():
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await checkpoint()
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return
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self._tasks.append(current_task())
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await suspend() # We get re-scheduled by set()
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@enable_ki_protection
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def set(self):
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"""
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Sets the event, awaking all tasks
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that called wait() on it
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"""
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if self.is_set():
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raise RuntimeError(
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"this event has already been set: create a new Event object instead"
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)
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self._set = True
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for waiter in self._tasks:
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current_loop().reschedule(waiter)
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self._tasks.clear()
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class Queue:
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"""
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An asynchronous FIFO queue
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"""
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def _put_item(self, item):
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self.container.append(item)
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def _get_item(self):
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return self.container.popleft()
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def __init__(self, maxsize: int | None = None):
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"""
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Object constructor
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"""
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self.maxsize = maxsize
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# Stores event objects for tasks wanting to
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# get items from the queue
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self.getters: deque[Event] = deque()
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# Stores event objects for tasks wanting to
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# put items on the queue
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self.putters: deque[Event] = deque()
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self.container: deque = deque()
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def __len__(self):
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"""
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Returns the length of the queue
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"""
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return len(self.container)
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def __repr__(self) -> str:
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return f"{self.__class__.__name__}({f', '.join(map(str, self.container))})"
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def __aiter__(self):
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"""
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Implements the asynchronous iterator protocol
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"""
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return self
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async def __anext__(self):
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"""
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Implements the asynchronous iterator protocol
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"""
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if len(self):
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return await self.get()
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else:
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raise StopAsyncIteration()
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@enable_ki_protection
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async def put(self, item: Any):
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"""
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Pushes an element onto the queue. If the
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queue is full, waits until a slot is
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available
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"""
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if self.maxsize and len(self.container) == self.maxsize:
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self.putters.append(Event())
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await self.putters[-1].wait()
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if self.getters:
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self.getters.popleft().set()
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self._put_item(item)
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await checkpoint()
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@enable_ki_protection
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async def get(self) -> Any:
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"""
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Pops an element off the queue. Blocks until
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an element is put onto it if the queue is empty
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"""
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if not self.container:
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self.getters.append(Event())
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await self.getters[-1].wait()
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if self.putters:
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self.putters.popleft().set()
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result = self._get_item()
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await checkpoint()
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return result
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@enable_ki_protection
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def get_noblock(self) -> Any:
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"""
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Equivalent of get(), but it raises
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structio.WouldBlock if there's no
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elements on the queue instead of
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blocking
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"""
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if not self.container:
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raise WouldBlock()
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if self.putters:
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self.putters.popleft().set()
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return self._get_item()
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@enable_ki_protection
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def put_noblock(self, item: Any):
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"""
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Equivalent of put(), but it raises
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structio.WouldBlock if there's not
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enough space on the queue instead
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of blocking
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"""
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if self.maxsize and len(self.container) == self.maxsize:
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raise WouldBlock()
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if self.getters:
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self.getters.popleft().set()
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self._put_item(item)
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def clear(self):
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"""
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Clears the queue
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"""
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self.container.clear()
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def reset(self):
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"""
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Resets the queue
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"""
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self.clear()
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self.getters.clear()
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self.putters.clear()
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class LIFOQueue(Queue):
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"""
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A LIFO variant of the regular Queue class
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"""
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def __init__(self, maxsize: int):
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super().__init__(maxsize)
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def _get_item(self):
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return self.container.pop()
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class PriorityQueue(Queue):
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"""
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A queue with built-in priority. Lowest-priority
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items are retrieved first. The items to be stored
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in the queue must be comparable: consider using a
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wrapper dataclass if they aren't, as shown [here](https://docs.python.org/3/library/queue.html#queue.PriorityQueue)
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"""
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def __init__(self, maxsize: int):
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super().__init__(maxsize)
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self.container: list[Any] = []
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def _get_item(self):
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return heappop(self.container)
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def _put_item(self, item):
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heappush(self.container, item)
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class MemoryReceiveChannel(ReadableChannel):
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"""
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An in-memory one-way channel to read
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data
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"""
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def __init__(self, buffer):
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self._buffer = buffer
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self._closed = False
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@enable_ki_protection
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async def receive(self):
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if self._closed:
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raise ResourceClosed("cannot operate on a closed channel")
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return await self._buffer.get()
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@enable_ki_protection
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async def close(self):
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self._closed = True
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await checkpoint()
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def pending(self):
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return bool(self._buffer)
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def readers(self):
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return len(self._buffer.getters)
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class MemorySendChannel(WritableChannel):
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"""
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An in-memory one-way channel to send
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data
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"""
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def __init__(self, buffer):
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self._buffer = buffer
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self._closed = False
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@enable_ki_protection
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async def send(self, item):
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if self._closed:
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raise ResourceClosed("cannot operate on a closed channel")
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return await self._buffer.put(item)
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@enable_ki_protection
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async def close(self):
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self._closed = True
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await checkpoint()
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def pending(self):
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return bool(self._buffer)
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def writers(self):
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return len(self._buffer.putters)
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class MemoryChannel(Channel):
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"""
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An in-memory, two-way channel between
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tasks with optional buffering
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"""
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def __init__(self, buffer_size):
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self._buffer = Queue(buffer_size)
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self.reader = MemoryReceiveChannel(self._buffer)
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self.writer = MemorySendChannel(self._buffer)
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def pending(self):
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return self.reader.pending()
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def readers(self):
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return self.reader.readers()
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def writers(self):
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return self.writer.writers()
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async def send(self, value):
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await self.writer.send(value)
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async def receive(self):
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return await self.reader.receive()
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@enable_ki_protection
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async def close(self):
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await self.reader.close()
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await self.writer.close()
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class Semaphore:
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"""
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An asynchronous integer semaphore. The use of initial_size
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is for semaphores which we know that can grow up to max_size
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but that can't right now, say because there's too much load on
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the application and resources are constrained. If it is None,
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initial_size equals max_size
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"""
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def __init__(self, max_size: int, initial_size: int | None = None):
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if initial_size is None:
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initial_size = max_size
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assert initial_size <= max_size
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self.max_size = max_size
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# We use an unbuffered memory channel to pause
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# as necessary, kinda like socket.set_wakeup_fd
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# or something? Anyway I think it's pretty nifty
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# because we're doing no I/O whatsoever so things
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# stay pretty damn efficient (and cheap!)
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self.channel: MemoryChannel = MemoryChannel(0)
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self._counter: int = initial_size
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def __repr__(self):
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return f"<structio.Semaphore max_size={self.max_size} size={self._counter}>"
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@property
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def size(self) -> int:
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return self._counter
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@enable_ki_protection
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async def acquire(self):
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"""
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Acquires the semaphore, possibly
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blocking if the task counter is
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exhausted
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"""
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if self._counter == 0:
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await self.channel.receive()
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self._counter -= 1
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await checkpoint()
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@enable_ki_protection
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async def release(self):
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"""
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Releases a slot in the semaphore. Raises RuntimeError
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if there are no occupied slots to release
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"""
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if self._counter == self.max_size:
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raise RuntimeError("semaphore is not acquired")
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self._counter += 1
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if self.channel.readers():
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await self.channel.send(None)
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else:
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await checkpoint()
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@enable_ki_protection
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async def __aenter__(self):
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await self.acquire()
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return self
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@enable_ki_protection
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async def __aexit__(self, exc_type, exc_val, exc_tb):
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await self.release()
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class Lock:
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"""
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An asynchronous single-owner task lock. Unlike
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the lock in threading.Thread, only the lock's
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owner can release it
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"""
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def __init__(self):
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self._owner: Task | None = None
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self._sem: Semaphore = Semaphore(1)
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@property
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def owner(self) -> Task | None:
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"""
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Returns the current owner of the lock,
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or None if the lock is not being held
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"""
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return self._owner
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@property
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def locked(self) -> bool:
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"""
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Returns whether the lock is currently
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held
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"""
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return self._sem.size == 0
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@enable_ki_protection
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async def acquire(self):
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"""
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Acquires the lock, possibly
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blocking until it is available
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"""
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await self._sem.acquire()
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self._owner = current_task()
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@enable_ki_protection
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async def release(self):
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"""
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Releases the lock if it was previously
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acquired by the caller. If the lock is
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not currently acquired or if it is not
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acquired by the calling task, RuntimeError
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is raised
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"""
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if not self.owner:
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raise RuntimeError("lock is not acquired")
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if current_task() is not self.owner:
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raise RuntimeError("lock can only be released by the owner")
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self._owner = None
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await self._sem.release()
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@enable_ki_protection
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async def __aenter__(self):
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await self.acquire()
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return self
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@enable_ki_protection
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async def __aexit__(self, exc_type, exc_val, exc_tb):
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await self.release()
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class RLock(Lock):
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"""
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An asynchronous, single-owner recursive lock.
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Recursive locks have the property that their
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acquire() method can be called multiple times
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by the owner without deadlocking: each call
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increments an internal counter, which is decremented
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at every call to release(). The lock is released only
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when the internal counter reaches zero
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"""
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def __init__(self):
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super().__init__()
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self._acquire_count = 0
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@enable_ki_protection
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async def acquire(self):
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current = current_task()
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if self.owner != current:
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await super().acquire()
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else:
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await checkpoint()
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self._acquire_count += 1
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@property
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def acquire_count(self) -> int:
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"""
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Returns the number of times acquire()
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was called by the owner (note that it
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may be zero if the lock is not being
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held)
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"""
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return self._acquire_count
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@enable_ki_protection
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async def release(self):
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# I hate the repetition, but it's the
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# only way to make sure that a task can't
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# decrement the counter of a lock it does
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# not own
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current = current_task()
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if self.owner != current:
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await super().release()
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else:
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self._acquire_count -= 1
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if self._acquire_count == 0:
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await super().release()
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else:
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await checkpoint()
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