unix: Implement PEP 475 to retry syscalls failing with EINTR.

https://www.python.org/dev/peps/pep-0475/

This implements something similar to PEP 475 on the unix port, and for the
VfsPosix class.

There are a few differences from the CPython implementation:
- Since we call mp_handle_pending() between any ENITR's, additional
  functions could be called if MICROPY_ENABLE_SCHEDULER is enabled, not
  just signal handlers.
- CPython only handles signal on the main thread, so other threads will
  raise InterruptedError instead of retrying.  On MicroPython,
  mp_handle_pending() will currently raise exceptions on any thread.

A new macro MP_HAL_RETRY_SYSCALL is introduced to reduce duplicated code
and ensure that all instances behave the same.  This will also allow other
ports that use POSIX-like system calls (and use, eg, VfsPosix) to provide
their own implementation if needed.

0 files changed, 0 insertions, 0 deletions