mirror of https://github.com/nocturn9x/giambio.git
336 lines
12 KiB
Python
336 lines
12 KiB
Python
"""
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Copyright (C) 2020 nocturn9x
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Licensed under the Apache License, Version 2.0 (the "License");
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you may not use this file except in compliance with the License.
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You may obtain a copy of the License at
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http://www.apache.org/licenses/LICENSE-2.0
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Unless required by applicable law or agreed to in writing, software
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distributed under the License is distributed on an "AS IS" BASIS,
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WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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See the License for the specific language governing permissions and
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limitations under the License.
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"""
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# Import libraries and internal resources
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import types
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from collections import defaultdict
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from selectors import DefaultSelector, EVENT_READ, EVENT_WRITE
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import socket
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from .exceptions import AlreadyJoinedError, CancelledError, ResourceBusy, GiambioError
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from timeit import default_timer
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from time import sleep as wait
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from .socket import AsyncSocket, WantWrite, WantRead
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from ._layers import Task, TimeQueue
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from socket import SOL_SOCKET, SO_ERROR
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from ._traps import want_read, want_write
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import traceback, sys
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class AsyncScheduler:
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"""
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An asynchronous scheduler toy implementation. Tries to mimic the threaded
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model in its simplicity, without using actual threads, but rather alternating
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across coroutines execution to let more than one thing at a time to proceed
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with its calculations. An attempt to fix the threaded model underlying pitfalls
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and weaknesses has been made, without making the API unnecessarily complicated.
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A few examples are tasks cancellation and exception propagation.
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Can perform (unreliably) socket I/O asynchronously.
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"""
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def __init__(self):
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"""Object constructor"""
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self.tasks = [] # Tasks that are ready to run
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self.selector = DefaultSelector() # Selector object to perform I/O multiplexing
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self.current_task = None # This will always point to the currently running coroutine (Task object)
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self.joined = (
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{}
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) # Maps child tasks that need to be joined their respective parent task
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self.clock = (
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default_timer # Monotonic clock to keep track of elapsed time reliably
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)
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self.some_cancel = False
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self.paused = TimeQueue(self.clock) # Tasks that are asleep
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self.events = set() # All Event objects
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self.event_waiting = defaultdict(list) # Coroutines waiting on event objects
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self.sequence = 0
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def _run(self):
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"""
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Starts the loop and 'listens' for events until there are either ready or asleep tasks,
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then exit. This behavior kinda reflects a kernel, as coroutines can request
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the loop's functionality only trough some fixed entry points, which in turn yield and
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give execution control to the loop itself.
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"""
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while True:
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try:
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if not self.selector.get_map() and not any(
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[self.paused, self.tasks, self.event_waiting]
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): # If there is nothing to do, just exit
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break
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elif not self.tasks:
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if self.paused:
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# If there are no actively running tasks, we try to schedule the asleep ones
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self._check_sleeping()
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if self.selector.get_map():
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self._check_io() # The next step is checking for I/O
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if self.event_waiting:
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# Try to awake event-waiting tasks
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self._check_events()
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while self.tasks: # While there are tasks to run
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self.current_task = self.tasks.pop(0)
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if self.some_cancel:
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self._check_cancel()
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# Sets the currently running task
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method, *args = self.current_task.run() # Run a single step with the calculation
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self.current_task.status = "run"
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getattr(self, f"_{method}")(*args)
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# Sneaky method call, thanks to David Beazley for this ;)
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except CancelledError:
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self.current_task.cancelled = True
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self._reschedule_parent()
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except StopIteration as e: # Coroutine ends
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self.current_task.result = e.args[0] if e.args else None
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self.current_task.finished = True
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self._reschedule_parent()
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except RuntimeError:
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continue
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except BaseException as error: # Coroutine raised
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print(error)
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self.current_task.exc = error
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self._reschedule_parent()
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self._join(self.current_task)
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raise
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def _check_cancel(self):
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"""
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Checks for task cancellation
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"""
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if self.current_task.status == "cancel": # Deferred cancellation
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self.current_task.cancelled = True
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self.current_task.throw(CancelledError(self.current_task))
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def _check_events(self):
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"""
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Checks for ready or expired events and triggers them
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"""
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for event, tasks in self.event_waiting.copy().items():
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if event._set:
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event.event_caught = True
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self.tasks.extend(tasks + [event.notifier])
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self.event_waiting.pop(event)
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def _check_sleeping(self):
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"""
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Checks and reschedules sleeping tasks
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"""
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wait(max(0.0, self.paused[0][0] - self.clock()))
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# Sleep until the closest deadline in order not to waste CPU cycles
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while self.paused[0][0] < self.clock():
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# Reschedules tasks when their deadline has elapsed
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self.tasks.append(self.paused.get())
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if not self.paused:
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break
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def _check_io(self):
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"""
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Checks and schedules task to perform I/O
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"""
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timeout = 0.0 if self.tasks else None
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# If there are no tasks ready wait indefinitely
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io_ready = self.selector.select(timeout)
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# Get sockets that are ready and schedule their tasks
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for key, _ in io_ready:
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self.tasks.append(key.data) # Resource ready? Schedule its task
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def start(self, func: types.FunctionType, *args):
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"""
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Starts the event loop from a sync context
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"""
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entry = Task(func(*args))
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self.tasks.append(entry)
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self._join(entry) # TODO -> Inspect this line, does it actually do anything useful?
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self._run()
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return entry
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def _reschedule_parent(self):
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"""
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Reschedules the parent task of the
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currently running task, if any
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"""
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parent = self.joined.pop(self.current_task, None)
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if parent:
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self.tasks.append(parent)
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return parent
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# TODO: More generic I/O rather than just sockets
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def _want_read(self, sock: socket.socket):
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"""
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Handler for the 'want_read' event, registers the socket inside the selector to perform I/0 multiplexing
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"""
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self.current_task.status = "I/O"
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if self.current_task._last_io:
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if self.current_task._last_io == ("READ", sock):
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return # Socket is already scheduled!
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else:
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self.selector.unregister(sock)
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self.current_task._last_io = "READ", sock
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try:
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self.selector.register(sock, EVENT_READ, self.current_task)
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except KeyError: # The socket is already registered doing something else
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raise ResourceBusy("The given resource is busy!") from None
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def _want_write(self, sock: socket.socket):
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"""
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Handler for the 'want_write' event, registers the socket inside the selector to perform I/0 multiplexing
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"""
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self.current_task.status = "I/O"
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if self.current_task._last_io:
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if self.current_task._last_io == ("WRITE", sock):
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return # Socket is already scheduled!
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else:
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self.selector.unregister(sock) # modify() causes issues
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self.current_task._last_io = "WRITE", sock
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try:
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self.selector.register(sock, EVENT_WRITE, self.current_task)
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except KeyError:
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raise ResourceBusy("The given resource is busy!") from None
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def _join(self, child: types.coroutine):
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"""
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Handler for the 'join' event, does some magic to tell the scheduler
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to wait until the passed coroutine ends. The result of this call equals whatever the
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coroutine returns or, if an exception gets raised, the exception will get propagated inside the
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parent task
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"""
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if child.cancelled or child.exc: # Task was cancelled or has errored
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self._reschedule_parent()
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elif child.finished: # Task finished running
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self.tasks.append(self.current_task) # Task has already finished
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else:
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if child not in self.joined:
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self.joined[child] = self.current_task
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else:
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raise AlreadyJoinedError(
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"Joining the same task multiple times is not allowed!"
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)
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def _sleep(self, seconds: int or float):
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"""
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Puts the caller to sleep for a given amount of seconds
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"""
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if seconds:
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self.current_task.status = "sleep"
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self.paused.put(self.current_task, seconds)
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else:
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self.tasks.append(self.current_task)
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def _event_set(self, event):
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"""
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Sets an event
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"""
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event.notifier = self.current_task
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event._set = True
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self.events.add(event)
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def _event_wait(self, event):
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"""
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Waits for an event
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"""
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if event in self.events:
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event.waiting -= 1
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if event.waiting <= 0:
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return self.events.remove(event)
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else:
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return
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else:
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self.event_waiting[event].append(self.current_task)
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def _cancel(self, task):
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"""
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Handler for the 'cancel' event, throws CancelledError inside a coroutine
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in order to stop it from executing. The loop continues to execute as tasks
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are independent
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"""
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if not self.some_cancel:
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self.some_cancel = True
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task.status = "cancel" # Cancellation is deferred
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def wrap_socket(self, sock):
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"""
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Wraps a standard socket into an AsyncSocket object
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"""
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return AsyncSocket(sock, self)
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async def _read_sock(self, sock: socket.socket, buffer: int):
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"""
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Reads from a socket asynchronously, waiting until the resource is available and returning up to buffer bytes
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from the socket
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"""
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await want_read(sock)
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try:
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return sock.recv(buffer)
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except WantRead:
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await want_write(sock)
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return sock.recv(buffer)
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async def _accept_sock(self, sock: socket.socket):
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"""
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Accepts a socket connection asynchronously, waiting until the resource is available and returning the
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result of the accept() call
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"""
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await want_read(sock)
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return sock.accept()
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async def _sock_sendall(self, sock: socket.socket, data: bytes):
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"""
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Sends all the passed data, as bytes, trough the socket asynchronously
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"""
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while data:
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await want_write(sock)
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sent_no = sock.send(data)
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data = data[sent_no:]
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async def _close_sock(self, sock: socket.socket):
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"""
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Closes the socket asynchronously
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"""
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await want_write(sock)
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self.selector.unregister(sock)
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return sock.close()
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async def _connect_sock(self, sock: socket.socket, addr: tuple):
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"""
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Connects a socket asynchronously
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"""
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try: # "Borrowed" from curio
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return sock.connect(addr)
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except WantWrite:
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await want_write(sock)
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err = sock.getsockopt(SOL_SOCKET, SO_ERROR)
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if err != 0:
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raise OSError(err, f"Connect call failed: {addr}")
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