POSIX doesn't guarantee something like that to work, but it works on any
system with careful signal implementation. Roughly, the requirement is
that signal handler is executed in the context of the process, its main
thread, etc. This is true for Linux. Also tested to work without issues
on MacOSX.
This basically introduces the MICROPY_MACHINE_MEM_GET_READ_ADDR
and MICROPY_MACHINE_MEM_GET_WRITE_ADDR macros. If one of them is
not defined, then a default identity function is provided.
To let unix port implement "machine" functionality on Python level, and
keep consistent naming in other ports (baremetal ports will use magic
module "symlinking" to still load it on "import machine").
Fixes#1701.
This solves long-standing non-deterministic bug, which manifested itself
on x86 32-bit (at least of reported cases) - segfault on Ctrl+C (i.e.
SIGINT).
ilistdir() returns iterator which yields triples of (name, type, ino)
where ino is inode number for entry's data, type of entry (file/dir/etc.),
and name of file/dir. listdir() can be easily implemented in terms of this
iterator (which is otherwise more efficient in terms of memory use and may
save expensive call to stat() for each returned entry).
CPython has os.scandir() which also returns an iterator, but it yields
more complex objects of DirEntry type. scandir() can also be easily
implemented in terms of ilistdir().
After an I/O event is triggered for fd, event flags are automatically reset,
so no further events are reported until new event flags are set. This is
an optimization for uasyncio, required to account for coroutine semantics:
each coroutine issues explicit read/write async call, and once that trigger,
no events should be reported to coroutine, unless it again explicitly
requests it. One-shot mode saves one linear scan over the poll array.
Per CPython docs, "Registering a file descriptor that’s already registered
is not an error, and has the same effect as registering the descriptor
exactly once."
https://docs.python.org/3/library/select.html#select.poll.register
That's somewhat ambiguous, what's implemented here is that if fd si not
yet registered, it is registered. Otherwise, the effect is equivalent to
modify() method.
Usually this checking is done by VM on jump instructions, but for linear
sequences of instructions and builtin functions this won't happen. Particular
target of this change is long-running builtin functions like time.sleep().
As set by signal handler. This assumes that exception will be raised
somewhere else, which so far doesn't happen for single function call.
Still, it makes sense to handle that in some common place.
This allows the mp_obj_t type to be configured to something other than a
pointer-sized primitive type.
This patch also includes additional changes to allow the code to compile
when sizeof(mp_uint_t) != sizeof(void*), such as using size_t instead of
mp_uint_t, and various casts.
THis is required to deal well with signals, signals being the closest
analogue of hardware interrupts for POSIX. This is also CPython 3.5
compliant behavior (PEP 475).
The main problem implementing this is to figure out how much time was
spent in waiting so far/how much is remaining. It's well-known fact that
Linux updates select()'s timeout value when returning with EINTR to the
remaining wait time. Here's what POSIX-based standards say about this:
(http://pubs.opengroup.org/onlinepubs/9699919799/functions/pselect.html):
"Upon successful completion, the select() function may modify the object
pointed to by the timeout argument."
I.e. it allows to modify timeout value, but doesn't say how exactly it is
modified. And actually, it allows such modification only "upon successful
completion", which returning with EINTR error hardly is.
POSIX also allows to request automatic EINTR restart for system calls using
sigaction call with SA_RESTART flag, but here's what the same document says
about it:
"If SA_RESTART has been set for the interrupting signal, it is
implementation-defined whether the function restarts or returns with
[EINTR]."
In other words, POSIX doesn't leave room for both portable and efficient
handling of this matter, so the code just allows to manually select
Linux-compatible behavior with MICROPY_SELECT_REMAINING_TIME option,
or otherwise will just raise OSError. When systems with non-Linux behavior
are found, they can be handled separately.
In other words, unix port now uses overriden printf(), instead of using
libc's. This should remove almost all dependency on libc stdio (which
is bloated).
