path: root/nemesis/causal_event_loop.py

'''
Copyright 2025 bdunahu

   Licensed under the Apache License, Version 2.0 (the "License");
   you may not use this file except in compliance with the License.
   You may obtain a copy of the License at

       http://www.apache.org/licenses/LICENSE-2.0

   Unless required by applicable law or agreed to in writing, software
   distributed under the License is distributed on an "AS IS" BASIS,
   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   See the License for the specific language governing permissions and
   limitations under the License.

Commentary:

Code:
'''

import asyncio
import collections
from sortedcontainers import SortedList
import heapq
import selectors
import time
import traceback
from copy import copy
from asyncio.log import logger
from asyncio import Task, events
from asyncio.base_events import _format_handle

_MIN_SCHEDULED_TIMER_HANDLES = 100
_MIN_CANCELLED_TIMER_HANDLES_FRACTION = 0.5
MAXIMUM_SELECT_TIMEOUT = 24 * 3600


orig_handle = asyncio.events.Handle

class TimeAwareMixin:

    # the timestamp this callback was registered
    register_time = None
    # the timestamp this callback completed i/o
    _when = None
    # the timestamp this callback entered the pause buffer
    time_entered_pause_buffer = None

    def __init__(self):
        self.register_time = time.monotonic()

    def __hash__(self):
        return hash(self._when)

    def __lt__(self, other):
        if isinstance(other, orig_handle):
            return self._when < other._when
        return NotImplemented

    def __le__(self, other):
        if isinstance(other, orig_handle):
            return self._when < other._when or self.__eq__(other)
        return NotImplemented

    def __gt__(self, other):
        if isinstance(other, orig_handle):
            return self._when > other._when
        return NotImplemented

    def __ge__(self, other):
        if isinstance(other, orig_handle):
            return self._when > other._when or self.__eq__(other)
        return NotImplemented


def create_subclass(base_class):
    class NewSubclass(base_class, TimeAwareMixin):
        def __init__(self, *args, **kwargs):
            super().__init__(*args, **kwargs)
            TimeAwareMixin.__init__(self)

    return NewSubclass


# make all the subclasses inherit from TimeAwareHandle as well
for sc in [orig_handle] + orig_handle.__subclasses__():
    subclass = create_subclass(sc)
    setattr(asyncio.events, sc.__name__, subclass)

class CausalEventLoop(asyncio.SelectorEventLoop):

    # a value between 0 and 1. 0 means no optimization,
    # 1 means the target coroutine is optimized away entirely
    _speedup = 1.0
    # a list of callbacks which have recently completed
    _pause_buffer = SortedList()
    # a list of intervals in which the target coroutine has been active
    _coro_intervals = SortedList()
    # a list of completed callbacks, and their associated queue time
    _completed_coros = []
    # the last time we entered the target coro
    _time_entered_coro = None
    _ready_events = []

    def __init__(self) -> None:
        super().__init__()

    def set_speedup(self, speedup):
        self._speedup = speedup

        # reset experiment counters
        self._time_entered_coro = None
        self._coro_intervals.clear()
        self._completed_coros.clear()

    def get_completed_coros(self):
        return self._completed_coros

    def get_pause_time(self):
        if not self._coro_intervals:
            return 0

        start_interval = self._coro_intervals[0][0]
        end_interval = self.time() if self._time_entered_coro else self._coro_intervals[-1][1]
        interval = (start_interval, end_interval)
        return self._get_pause_time(interval)

    def ping_enter_coro(self):
        self._time_entered_coro = self.time()

    def ping_exit_coro(self):
        assert isinstance(self._time_entered_coro, float), f"Tried to exit coro before recorded entry!"
        self._coro_intervals.add((self._time_entered_coro, self.time()))
        self._time_entered_coro = None

    def collect_ready_events(self, timeout=0):
        event_list = self._selector.select(timeout)
        self._ready_events.append((event_list, self.time()))

    def update_ready(self):
        '''
        Polls the IO selector, schedules resulting callbacks, and schedules
        'call_later' callbacks.
        '''
        curr_time = self.time()
        sched_count = len(self._scheduled)
        if (sched_count > _MIN_SCHEDULED_TIMER_HANDLES and
            self._timer_cancelled_count / sched_count >
            _MIN_CANCELLED_TIMER_HANDLES_FRACTION):
            # Remove delayed calls that were cancelled if their number
            # is too high
            new_scheduled = []
            for handle in self._scheduled:
                if handle._cancelled:
                    handle._scheduled = False
                else:
                    new_scheduled.append(handle)

            heapq.heapify(new_scheduled)
            self._scheduled = new_scheduled
            self._timer_cancelled_count = 0
        else:
            # Remove delayed calls that were cancelled from head of queue.
            while self._scheduled and self._scheduled[0]._cancelled:
                self._timer_cancelled_count -= 1
                handle = heapq.heappop(self._scheduled)
                handle._scheduled = False

        timeout = None
        if self._ready or self._stopping:
            timeout = 0
        else:
            curr_time = self.time()
            if self._scheduled:
                # Compute the desired timeout.
                # requires computing our-best guess arrival time
                handle = self._scheduled[0]
                timeout = (handle._when + self._get_pause_for_io(handle, curr_time)) \
                    - curr_time
                timeout = max(0, min(timeout, MAXIMUM_SELECT_TIMEOUT))
            if self._pause_buffer:
                # pause buffer has an exact arrival time
                pause_timeout = self._pause_buffer[0]._when - curr_time
                timeout = min(pause_timeout, timeout) if timeout else pause_timeout
                timeout = max(0, min(timeout, MAXIMUM_SELECT_TIMEOUT))

        self.collect_ready_events(timeout)
        for event_list in self._ready_events:
            self._process_events(*event_list)

        # Handle 'later' callbacks that are ready.
        curr_time = self.time()
        end_time = curr_time + self._clock_resolution
        while self._scheduled:
            handle = self._scheduled[0]
            when = handle._when
            if when >= end_time:
                break
            handle = heapq.heappop(self._scheduled)
            handle._scheduled = False

            time_to_buffer = when + self._get_pause_for_io(handle, curr_time)
            handle._when = time_to_buffer
            handle.time_entered_pause_buffer = curr_time
            self._pause_buffer.add(handle)

        # handle callbacks which can leave pause timeout
        while self._pause_buffer:
            handle = self._pause_buffer[0]
            if handle._when >= end_time:
                break
            # pop the first item in the list
            handle = self._pause_buffer.pop(0)

            # if we paused during buffering, we need to delay again
            # TODO clean this up
            # this whole file has 'rounding' timing errors :(
            handle._when = handle._when + \
                self._get_pause_for_pause_time(handle, curr_time)
            if handle._when >= end_time:
                handle.time_entered_pause_buffer = curr_time
                self._pause_buffer.add(handle)
            else:
                self._ready.append(handle)

    def _run_once(self):
        """
        Run one full iteration of the event loop.

        This calls all currently ready callbacks.
        """
        self.update_ready()

        # This is the only place where callbacks are actually *called*.
        # All other places just add them to ready.
        # Note: We run all currently scheduled callbacks, but not any
        # callbacks scheduled by callbacks run this time around --
        # they will be run the next time (after another I/O poll).
        # Use an idiom that is thread-safe without using locks.
        ntodo = len(self._ready)
        for i in range(ntodo):
            handle = self._ready.popleft()
            if handle._cancelled:
                continue
            try:
                self._current_handle = handle

                process_start_time = self.time()

                handle._run()

                process_end_time = self.time()
                dt = process_end_time - process_start_time
                if self._debug and dt >= self.slow_callback_duration:
                    logger.warning('Executing %s took %.3f seconds',
                                   _format_handle(handle), dt)

                time_interval = (handle._when, process_start_time)
                pause_time = self._get_pause_time(time_interval)
                adjusted_start_time = process_start_time - pause_time
                wait_time = adjusted_start_time - handle._when
                assert wait_time >= -0.0001, f"wait time on {_format_handle(handle)} was found to be {wait_time:.4f}!"
                self._completed_coros.append((_format_handle(handle), wait_time))
            except Exception:
                traceback.print_exc()
            finally:
                self._current_handle = None
            handle = None  # Needed to break cycles when an exception occurs.

    def _process_events(self, event_list, time):
        for key, mask in event_list:
            fileobj, (reader, writer) = key.fileobj, key.data
            if mask & selectors.EVENT_READ and reader is not None:
                if reader._cancelled:
                    self._remove_reader(fileobj)
                else:
                    time_to_buffer = time + \
                        self._get_pause_for_io(reader, time)
                    reader._when = time_to_buffer
                    self._add_callback(reader)
            if mask & selectors.EVENT_WRITE and writer is not None:
                if writer._cancelled:
                    self._remove_writer(fileobj)
                else:
                    time_to_buffer = time + \
                        self._get_pause_for_io(writer, time)
                    writer._when = time_to_buffer
                    self._add_callback(writer)

    def _call_soon(self, callback, args, context):
        handle = events.Handle(callback, args, self, context)
        if handle._source_traceback:
            del handle._source_traceback[-1]
        self._add_callback(handle)
        return handle

    def call_soon_threadsafe(self, callback, *args, context=None):
        """Like call_soon(), but thread-safe."""
        self._check_closed()
        if self._debug:
            self._check_callback(callback, 'call_soon_threadsafe')
        handle = events._ThreadSafeHandle(callback, args, self, context)
        self._add_callback(handle)
        if handle._source_traceback:
            del handle._source_traceback[-1]
        if handle._source_traceback:
            del handle._source_traceback[-1]
        self._write_to_self()
        return handle

    def _add_callback(self, handle):
        """Add a Handle to _pause_buffer."""
        if not handle._cancelled:
            curr_time = self.time()
            if not handle._when:
                handle._when = curr_time
            handle.time_entered_pause_buffer = curr_time
            self._pause_buffer.add(handle)

    def _get_pause_for_io(self, handle, io_time):
        time_interval = (handle.register_time, io_time)
        return self._get_pause_time(time_interval)

    def _get_pause_for_pause_time(self, handle, exit_time):
        time_interval = (handle.time_entered_pause_buffer, exit_time)
        return self._get_pause_time(time_interval)

    def _get_pause_time(self, cb_interval):
        time = 0
        start, end = cb_interval

        for coro_start, coro_end in self._coro_intervals:
            if start < coro_end and coro_start < end:
                time += self._get_overlap(start, end, coro_start, coro_end)
            # coro_intervals are sorted, so by this time all overlap has passed
            if end < coro_start:
                break

        curr_time = self.time()
        if self._time_entered_coro and \
           start < curr_time and self._time_entered_coro < end:
            time += self._get_overlap(start, end, self._time_entered_coro,
                                      curr_time)

        return time * self._speedup

    def _get_overlap(self, a_start, a_end, b_start, b_end):
        overlap_start = max(a_start, b_start)
        overlap_end = min(a_end, b_end)
        return overlap_end - overlap_start


class CausalEventLoopPolicy(asyncio.DefaultEventLoopPolicy):
    def new_event_loop(self):
        return CausalEventLoop()


asyncio.set_event_loop_policy(CausalEventLoopPolicy())