Before this patch the context manager's __aexit__() method would not be
executed if a return/break/continue statement was used to exit an async
with block. async with now has the same semantics as normal with.
The fix here applies purely to the compiler, and does not modify the
runtime at all. It might (eventually) be better to define new bytecode(s)
to handle async with (and maybe other async constructs) in a cleaner, more
efficient way.
One minor drawback with addressing this issue purely in the compiler is
that it wasn't possible to get 100% CPython semantics. The thing that is
different here to CPython is that the __aexit__ method is not looked up in
the context manager until it is needed, which is after the body of the
async with statement has executed. So if a context manager doesn't have
__aexit__ then CPython raises an exception before the async with is
executed, whereas uPy will raise it after it is executed. Note that
__aenter__ is looked up at the beginning in uPy because it needs to be
called straightaway, so if the context manager isn't a context manager then
it'll still raise an exception at the same location as CPython. The only
difference is if the context manager has the __aenter__ method but not the
__aexit__ method, then in that case uPy has different behaviour. But this
is a very minor, and acceptable, difference.
This patch is a code optimisation, trading text bytes for speed. On
pyboard it's an increase of 0.06% in code size for a gain (in pystone
performance) of roughly 6.5%.
The patch optimises load/store/delete of attributes in user defined classes
by not looking up special accessors (@property, __get__, __delete__,
__set__, __setattr__ and __getattr_) if they are guaranteed not to exist in
the class.
Currently, if you do my_obj.foo() then the runtime has to do a few checks
to see if foo is a property or has __get__, and if so delegate the call.
And for stores things like my_obj.foo = 1 has to first check if foo is a
property or has __set__ defined on it.
Doing all those checks each and every time the attribute is accessed has a
performance penalty. This patch eliminates all those checks for cases when
it's guaranteed that the checks will always fail, ie no attributes are
properties nor have any special accessor methods defined on them.
To make this guarantee it checks all attributes of a user-defined class
when it is first created. If any of the attributes of the user class are
properties or have special accessors, or any of the base classes of the
user class have them, then it sets a flag in the class to indicate that
special accessors must be checked for. Then in the load/store/delete code
it checks this flag to see if it can take the shortcut and optimise the
lookup.
It's an optimisation that's pretty widely applicable because it improves
lookup performance for all methods of user defined classes, and stores of
attributes, at least for those that don't have special accessors. And, it
allows to enable descriptors with minimal additional runtime overhead if
they are not used for a particular user class.
There is one restriction on dynamic class creation that has been introduced
by this patch: a user-defined class cannot go from zero special accessors
to one special accessor (or more) after that class has been subclassed. If
the script attempts this an AttributeError is raised (see addition to
tests/misc/non_compliant.py for an example of this case).
The cost in code space bytes for the optimisation in this patch is:
unix x64: +528
unix nanbox: +508
stm32: +192
cc3200: +200
esp8266: +332
esp32: +244
Performance tests that were done:
- on unix x86-64, pystone improved by about 5%
- on pyboard, pystone improved by about 6.5%, from 1683 up to 1794
- on pyboard, bm_chaos (from CPython benchmark suite) improved by about 5%
- on esp32, pystone improved by about 30% (but there are caching effects)
- on esp32, bm_chaos improved by about 11%
The string "Q+?" is special in that it hashes to zero with the djb2
algorithm (among other strings), and a zero hash should be incremented to a
hash of 1.
The case of a return statement in the try suite of a try-except statement
was previously only tested by builtin_compile.py, and only then in the part
of this test which checked for the existence of the compile builtin. So
this patch adds an explicit unit test for this case.
The VM expects that, if mp_resume() returns MP_VM_RETURN_EXCEPTION, then
the returned value is an exception instance (eg to add a traceback to it).
It's possible that a value passed to a generator's throw() is not an
exception so must be explicitly checked for if the thrown value is not
intercepted by the generator.
Thanks to @jepler for finding the bug.
Prior to this patch the code would crash if a key in a ** dict was anything
other than a str or qstr. This is because mp_setup_code_state() assumes
that keys in kwargs are qstrs (for efficiency).
Thanks to @jepler for finding the bug.
This patch concerns the handling of an NLR-raised StopIteration, raised
during a call to mp_resume() which is handling the yield from opcode.
Previously, commit 6738c1dded introduced code
to handle this case, along with a test. It seems that it was lucky that
the test worked because the code did not correctly handle the stack pointer
(sp).
Furthermore, commit 79d996a57b improved the
way mp_resume() propagated certain exceptions: it changed raising an NLR
value to returning MP_VM_RETURN_EXCEPTION. This change meant that the
test introduced in gen_yield_from_ducktype.py was no longer hitting the
code introduced in 6738c1dded.
The patch here does two things:
1. Fixes the handling of sp in the VM for the case that yield from is
interrupted by a StopIteration raised via NLR.
2. Introduces a new test to check this handling of sp and re-covers the
code in the VM.
Otherwise passing -1 as maxlen will lead to a zero allocation and
subsequent unbound buffer overflow in deque.append() because i_put is
allowed to grow without bound.
Prior to this patch uPy (on a 32-bit arch) would have severe issues when
calling bytes(-1): such a call would call vstr_init_len(vstr, -1) which
would then +1 on the len and call vstr_init(vstr, 0), which would then
round this up and allocate a small amount of memory for the vstr. The
bytes constructor would then attempt to zero out all this memory, thinking
it had allocated 2^32-1 bytes.
This patch improves the builtin dir() function by probing the target object
with all possible qstrs via mp_load_method_maybe. This is very simple (in
terms of implementation), doesn't require recursion, and allows to list all
methods of user-defined classes (without duplicates) even if they have
multiple inheritance with a common parent. The downside is that it can be
slow because it has to iterate through all the qstrs in the system, but
the "dir()" function is anyway mostly used for testing frameworks and user
introspection of types, so speed is not considered a priority.
In addition to providing a more complete implementation of dir(), this
patch is simpler than the previous implementation and saves some code
space:
bare-arm: -80
minimal x86: -80
unix x64: -56
unix nanbox: -48
stm32: -80
cc3200: -80
esp8266: -104
esp32: -64
This feature is not often used so is guarded by the config option
MICROPY_PY_BUILTINS_RANGE_BINOP which is disabled by default. With this
option disabled MicroPython will always return false when comparing two
range objects for equality (unless they are exactly the same object
instance). This does not match CPython so if (in)equality between range
objects is needed then this option should be enabled.
Enabling this option costs between 100 and 200 bytes of code space
depending on the machine architecture.
Note that the check for elem!=NULL is removed for the
MP_MAP_LOOKUP_ADD_IF_NOT_FOUND case because mp_map_lookup will always
return non-NULL for such a case.
This implements .pend_throw(exc) method, which sets up an exception to be
triggered on the next call to generator's .__next__() or .send() method.
This is unlike .throw(), which immediately starts to execute the generator
to process the exception. This effectively adds Future-like capabilities
to generator protocol (exception will be raised in the future).
The need for such a method arised to implement uasyncio wait_for() function
efficiently (its behavior is clearly "Future" like, and normally would
require to introduce an expensive Future wrapper around all native
couroutines, like upstream asyncio does).
py/objgenerator: pend_throw: Return previous pended value.
This effectively allows to store an additional value (not necessary an
exception) in a coroutine while it's not being executed. uasyncio has
exactly this usecase: to mark a coro waiting in I/O queue (and thus
not executed in the normal scheduling queue), for the purpose of
implementing wait_for() function (cancellation of such waiting coro
by a timeout).
"Builtin" tinytest-based testsuite as employed by qemu-arm (and now
generalized by me to be reusable for other targets) performs simplified
detection of skipped tests, it treats as such tests which raised SystemExit
(instead of checking got "SKIP" output). Consequently, each "SKIP" must
be accompanied by SystemExit (and conversely, SystemExit should not be
used if test is not skipped, which so far seems to be true).
Damien George