These are internal names and can be safely renamed without affecting user
code. push_sorted() and push_head() are merged into a single push()
method, which is already how the C version is implemented. pop_head() is
simply renamed to pop().
The changes are:
- q.push_sorted(task, t) -> q.push(task, t)
- q.push_head(task) -> q.push(task)
- q.pop_head() -> q.pop()
The shorter names and removal of push_head() leads to a code size reduction
of between 40 and 64 bytes on bare-metal targets.
Signed-off-by: Damien George <damien@micropython.org>
This implements a form of CPython's "add_done_callback()", but at this
stage it is a hidden feature and only intended to be used internally.
Signed-off-by: Damien George <damien@micropython.org>
This commit fixes a problem with a race between cancellation of task A and
completion of task B, when A waits on B. If task B completes just before
task A is cancelled then the cancellation of A does not work. Instead,
the CancelledError meant to cancel A gets passed through to B (that's
expected behaviour) but B handles it as a "Task exception wasn't retrieved"
scenario, printing out such a message (this is because finished tasks point
their "coro" attribute to themselves to indicate they are done, and
implement the throw() method, but that method inadvertently catches the
CancelledError). The correct behaviour is for B to bounce that
CancelledError back out.
This bug is mainly seen when wait_for() is used, and in that context the
symptoms are:
- occurs when using wait_for(T, S), if the task T being waited on finishes
at exactly the same time as the wait-for timeout S expires
- task T will have run to completion
- the "Task exception wasn't retrieved message" is printed with
"<class 'CancelledError'>" as the error (ie no traceback)
- the wait_for(T, S) call never returns (it's never put back on the
uasyncio run queue) and all tasks waiting on this are blocked forever
from running
- uasyncio otherwise continues to function and other tasks continue to be
scheduled as normal
The fix here reworks the "waiting" attribute of Task to be called "state"
and uses it to indicate whether a task is: running and not awaited on,
running and awaited on, finished and not awaited on, or finished and
awaited on. This means the task does not need to point "coro" to itself to
indicate finished, and also allows removal of the throw() method.
A benefit of this is that "Task exception wasn't retrieved" messages can go
back to being able to print the name of the coroutine function.
Fixes issue #7386.
Signed-off-by: Damien George <damien@micropython.org>
This is added because task.coro==None is no longer the way to detect if a
task is finished. Providing a (CPython compatible) function for this
allows the implementation to be abstracted away.
Signed-off-by: Damien George <damien@micropython.org>
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>
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.
Damien George
Damien George