mirror of https://github.com/nocturn9x/giambio.git
Temporary 'meh' fix to allow exception propagation to occur, deleted old _managers.py module and refactored comments and docstrings
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nocturn9x
parent
094e3d50ac
commit
5c5beeef22
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@ -3,6 +3,5 @@ __version__ = (0, 0, 1)
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from ._core import AsyncScheduler
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from .exceptions import GiambioError, AlreadyJoinedError, CancelledError
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from ._traps import sleep
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from ._managers import TaskManager
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__all__ = ["AsyncScheduler", "GiambioError", "AlreadyJoinedError", "CancelledError", "TaskManager", "sleep"]
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@ -1,3 +1,4 @@
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# Import libraries and internal resources
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import types
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from collections import deque
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from selectors import DefaultSelector, EVENT_READ, EVENT_WRITE
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@ -13,8 +14,15 @@ from ._traps import want_read, want_write
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class AsyncScheduler:
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"""Implementation of an event loop, alternates between execution of coroutines (asynchronous functions)
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to allow a concurrency model or 'green threads'"""
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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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@ -22,7 +30,7 @@ class AsyncScheduler:
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self.to_run = deque() # Tasks that are ready to run
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self.paused = [] # Tasks that are asleep
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self.selector = DefaultSelector() # Selector object to perform I/O multiplexing
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self.running = None # This will always point to the currently running coroutine (Task object)
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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 = {} # Maps child tasks that need to be joined their respective parent task
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self.clock = default_timer # Monotonic clock to keep track of elapsed time reliably
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self.sequence = 0 # A monotonically increasing ID to avoid some corner cases with deadlines comparison
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@ -34,62 +42,69 @@ class AsyncScheduler:
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give execution control to the loop itself."""
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while True:
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if not self.selector.get_map() and not any(deque(self.paused) + self.to_run):
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if not self.selector.get_map() and not any([self.paused, self.to_run]): # If there is nothing to do, just exit
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break
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if not self.to_run and self.paused: # If there are sockets ready, (re)schedule their associated task
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wait(max(0.0, self.paused[0][0] - self.clock())) # Sleep in order not to waste CPU cycles
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while self.paused[0][0] < self.clock(): # Reschedules task when their deadline has elapsed
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if not self.to_run and self.paused: # If there are no actively running tasks, we try to schedule the asleep ones
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wait(max(0.0, self.paused[0][0] - self.clock())) # Sleep until the closest deadline in order not to waste CPU cycles
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while self.paused[0][0] < self.clock(): # Reschedules tasks when their deadline has elapsed
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_, __, task = heappop(self.paused)
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self.to_run.append(task)
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if not self.paused:
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break
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timeout = 0.0 if self.to_run else None
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tasks = self.selector.select(timeout)
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timeout = 0.0 if self.to_run else None # If there are no tasks ready wait indefinitely
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tasks = self.selector.select(timeout) # Get sockets that are ready and schedule their tasks
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for key, _ in tasks:
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self.to_run.append(key.data) # Socket ready? Schedule the task
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self.selector.unregister(
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key.fileobj) # Once (re)scheduled, the task does not need to perform I/O multiplexing (for now)
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while self.to_run:
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self.running = self.to_run.popleft() # Sets the currently running task
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while self.to_run: # While there are tasks to run
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self.current_task = self.to_run.popleft() # Sets the currently running task
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try:
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method, *args = self.running.run()
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method, *args = self.current_task.run() # Run a single step with the calculation
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getattr(self, method)(*args) # Sneaky method call, thanks to David Beazley for this ;)
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except StopIteration as e:
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e = e.args[0] if e.args else None
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self.running.result = e
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self.running.finished = True
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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 CancelledError:
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self.running.cancelled = True
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except CancelledError: # Coroutine was cancelled
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self.current_task.cancelled = True
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self.reschedule_parent()
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except Exception as error:
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self.running.exc = error
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except Exception as error: # Coroutine raised
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self.current_task.exc = error
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self.reschedule_parent()
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raise # Find a better way to propagate errors
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def create_task(self, coro: types.coroutine):
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"""Spawns a child task"""
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task = Task(coro)
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self.to_run.append(task)
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return task
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def start(self, coro: types.coroutine):
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"""Starts the event loop using a coroutine as an entry point.
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Equivalent to self.create_task(coro) and self.run()
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"""
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self.to_run.append(Task(coro))
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self.create_task(coro)
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self.run()
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def reschedule_parent(self):
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"""Reschedules the parent task"""
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popped = self.joined.pop(self.running, None)
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popped = self.joined.pop(self.current_task, None)
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if popped:
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self.to_run.append(popped)
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def want_read(self, sock: socket.socket):
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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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self.selector.register(sock, EVENT_READ, self.running)
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self.selector.register(sock, EVENT_READ, self.current_task)
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def want_write(self, sock: socket.socket):
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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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self.selector.register(sock, EVENT_WRITE, self.running)
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self.selector.register(sock, EVENT_WRITE, self.current_task)
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def join(self, coro: types.coroutine):
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"""Handler for the 'join' event, does some magic to tell the scheduler
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@ -98,23 +113,22 @@ class AsyncScheduler:
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parent task"""
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if coro not in self.joined:
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self.joined[coro] = self.running
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self.joined[coro] = self.current_task
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else:
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raise AlreadyJoinedError("Joining the same task multiple times is not allowed!")
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def sleep(self, seconds):
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"""Puts a task to sleep"""
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"""Puts the caller to sleep for a given amount of seconds"""
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self.sequence += 1
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heappush(self.paused, (self.clock() + seconds, self.sequence, self.running))
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self.running = None
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heappush(self.paused, (self.clock() + seconds, self.sequence, self.current_task))
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def cancel(self, task):
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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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task.coroutine.throw(CancelledError)
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task.throw(CancelledError)
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def wrap_socket(self, sock):
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"""Wraps a standard socket into an AsyncSocket object"""
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@ -1,5 +1,5 @@
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import types
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from ._traps import join, sleep, cancel
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from ._traps import join, cancel
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class Task:
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@ -13,10 +13,15 @@ class Task:
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self.result = None
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self.finished = False
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def run(self):
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def run(self, what=None):
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"""Simple abstraction layer over the coroutines ``send`` method"""
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return self.coroutine.send(None)
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return self.coroutine.send(what)
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def throw(self, err: Exception):
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"""Simple abstraction layer over the coroutines ``throw`` method"""
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return self.coroutine.throw(err)
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async def join(self):
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"""Joins the task"""
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@ -28,11 +33,6 @@ class Task:
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await cancel(self)
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def result(self):
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if self.exc:
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raise self.exc
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return self.result
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def __repr__(self):
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"""Implements repr(self)"""
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@ -1,95 +0,0 @@
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from collections import deque
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import types
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from ._layers import Task
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from heapq import heappush
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class TaskManager:
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"""The only way to execute asynchronous code in giambio is trough a ``TaskManager`` (or one of its children classes) object used within
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an ``async with`` context manager. The ``TaskManager`` is an ideal "playground" where all asynchronous code runs and where giambio's
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event loop can control their execution flow.
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The key feature of this mechanism is that all tasks are always joined automatically: This opens a new world of features,
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allowing exceptions to propagate just as expected (exceptions are **never** discarded in giambio, unlike in some other libraries) and some other lower-level advantages.
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Moreover, giambio always saves the return values so that you don't lose any important information when executing a coroutine.
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There are a few concepts to explain here, though:
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- The term "task" refers to a coroutine executed trough the ``TaskManager``'s methods ``spawn()`` and ``schedule()``, as well as
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one executed with ``await coro()``
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- If an exception occurs, all other tasks are cancelled (read more below) and the exception is later propagated in the parent task
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- The concept of cancellation is a bit tricky, because there is no real way to stop a coroutine from executing without actually raising
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an exception inside i. So when giambio needs to cancel a task, it just throws ``giambio.exceptions.CancelledError`` inside it and hopes for the best.
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This exception inherits from ``BaseException``, which by convention means that it should not be catched. Doing so in giambio will likely break your code
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and make it explode spectacularly. If you really want to catch it to perform cleanup, be sure to re-raise it when done (or to raise another unhandled exception if you want)
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so that the internal loop can proceed with execution.
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In general, when writing an asynchronous function, you should always consider that it might be cancelled at any time and handle that case accordingly.
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"""
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def __init__(self, loop):
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self.values = {} # Results from each task
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self.loop = loop # The event loop that spawned the TaskManager
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async def _cancel_and_raise(self, exc):
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"""Cancels all the tasks inside the TaskManager object and raises the exception
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of the task that triggered this mechanism"""
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try:
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await self.loop.running.cancel()
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except Exception as error:
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self.loop.running.exc = error
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for task in self.loop.to_run + deque(self.loop.paused):
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if isinstance(task, tuple): # Sleeping task
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_, _, task = task
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try:
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await task.cancel()
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except Exception as error:
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task.exc = error
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raise exc
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async def __aenter__(self):
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return self
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async def __aexit__(self, type, value, traceback):
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while True:
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if not any([self.loop.to_run, self.loop.paused]):
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break
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tasks = self.loop.to_run + deque(self.loop.paused)
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task = tasks.popleft()
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if isinstance(task, tuple): # Sleeping task
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_, _, task = task
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self.values[task] = await task.join()
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if task.exc:
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print(task)
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await self._cancel_and_raise(task.exc)
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def spawn(self, coroutine: types.coroutine):
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"""Schedules a task for execution, appending it to the call stack
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:param coroutine: The coroutine to spawn, please note that if you want to execute foo, you need to pass foo() as this
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returns a coroutine instead of a function object
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:type coroutine: types.coroutine
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:returns: A ``Task`` object
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:rtype: class: Task
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"""
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task = Task(coroutine)
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self.loop.to_run.append(task)
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return task
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def schedule(self, coroutine: types.coroutine, n: int):
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"""Schedules a task for execution after when seconds
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:param coroutine: The coroutine to spawn, please note that if you want to execute foo, you need to pass foo() as this
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returns a coroutine instead of a function object
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:type coroutine: types.coroutine
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:param n: The delay in seconds after which the task should start running
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:type n: int
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:returns: A ``Task`` object
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:rtype: class: Task
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"""
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self.loop.sequence += 1
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task = Task(coroutine)
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heappush(self.loop.paused, (self.loop.clock() + n, self.loop.sequence, task))
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return task
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@ -32,8 +32,7 @@ def join(task):
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"""
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yield "join", task
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assert task.finished
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return task.result()
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return task.result
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@types.coroutine
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@ -1,4 +1,4 @@
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from giambio import AsyncScheduler, sleep, TaskManager
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from giambio import AsyncScheduler, sleep
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async def countdown(n: int):
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@ -7,7 +7,7 @@ async def countdown(n: int):
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n -= 1
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await sleep(1)
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if n == 5:
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raise ValueError('lul')
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raise ValueError('lul')
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print("Countdown over")
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@ -21,13 +21,17 @@ async def countup(stop, step: int or float = 1):
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async def main():
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async with TaskManager(scheduler) as manager:
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manager.spawn(countdown(10))
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manager.spawn(countup(5, 2))
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print("Counters started, awaiting completion")
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cup = scheduler.create_task(countdown(10))
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cdown = scheduler.create_task(countup(5, 2))
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print("Counters started, awaiting completion")
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await cup.join()
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await cdown.join()
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print("Task execution complete")
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if __name__ == "__main__":
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scheduler = AsyncScheduler()
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scheduler.start(main())
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try:
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scheduler.start(main())
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except Exception:
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print("main() errored!")
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@ -17,11 +17,10 @@ async def server(address: tuple):
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sock.listen(5)
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asock = sched.wrap_socket(sock)
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logging.info(f"Echo server serving asynchronously at {address}")
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async with giambio.TaskManager(sched) as manager:
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while True:
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conn, addr = await asock.accept()
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logging.info(f"{addr} connected")
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manager.spawn(echo_handler(conn, addr))
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while True:
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conn, addr = await asock.accept()
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logging.info(f"{addr} connected")
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task = sched.create_task(echo_handler(conn, addr))
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async def echo_handler(sock: AsyncSocket, addr: tuple):
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