When a tasks raises an exception which is uncaught, and no other task
await's on that task, then an error message is printed (or a user function
called) via a call to Loop.call_exception_handler. In CPython this call is
made when the Task object is freed (eg via reference counting) because it's
at that point that it is known that the exception that was raised will
never be handled.
MicroPython does not have reference counting and the current behaviour is
to deal with uncaught exceptions as early as possible, ie as soon as they
terminate the task. But this can be undesirable because in certain cases
a task can start and raise an exception immediately (before any await is
executed in that task's coro) and before any other task gets a chance to
await on it to catch the exception.
This commit changes the behaviour so that tasks which end due to an
uncaught exception are scheduled one more time for execution, and if they
are not await'ed on by the next scheduling loop, then the exception handler
is called (eg the exception is printed out).
Signed-off-by: Damien George <damien@micropython.org>
Otherwise a task that continuously awaits on a large negative sleep can
monopolise the scheduler (because its wake time is always less than
everything else in the pairing heap).
Signed-off-by: Damien George <damien@micropython.org>
This commit adds Loop.new_event_loop() which is used to reset the singleton
event loop. This functionality is put here instead of in Loop.close() to
make it possible to write code that is compatible with CPython.
This commit adds support for global exception handling in uasyncio
according to the CPython error handling:
https://docs.python.org/3/library/asyncio-eventloop.html#error-handling-api
This allows a program to receive exceptions from detached tasks and log
them to an appropriate location, instead of them being printed to the REPL.
The implementation preallocates a context dictionary so in case of an
exception there shouldn't be any RAM allocation.
The approach here is compatible with CPython except that in CPython the
exception handler is called once the task that threw an uncaught exception
is freed, whereas in MicroPython the exception handler is called
immediately when the exception is thrown.
Implements Task and TaskQueue classes in C, using a pairing-heap data
structure. Using this reduces RAM use of each Task, and improves overall
performance of the uasyncio scheduler.
This commit adds a completely new implementation of the uasyncio module.
The aim of this version (compared to the original one in micropython-lib)
is to be more compatible with CPython's asyncio module, so that one can
more easily write code that runs under both MicroPython and CPython (and
reuse CPython asyncio libraries, follow CPython asyncio tutorials, etc).
Async code is not easy to write and any knowledge users already have from
CPython asyncio should transfer to uasyncio without effort, and vice versa.
The implementation here attempts to provide good compatibility with
CPython's asyncio while still being "micro" enough to run where MicroPython
runs. This follows the general philosophy of MicroPython itself, to make it
feel like Python.
The main change is to use a Task object for each coroutine. This allows
more flexibility to queue tasks in various places, eg the main run loop,
tasks waiting on events, locks or other tasks. It no longer requires
pre-allocating a fixed queue size for the main run loop.
A pairing heap is used to queue Tasks.
It's currently implemented in pure Python, separated into components with
lazy importing for optional components. In the future parts of this
implementation can be moved to C to improve speed and reduce memory usage.
But the aim is to maintain a pure-Python version as a reference version.
