* bpo-30807: signal.setitimer() may disable the timer by mistake

* Add NEWS blurb

* Improve signal delivery

Avoid using Py_AddPendingCall from signal handler, to avoid calling signal-unsafe functions.

* Remove unused function

* Improve comments

* Add stress test

* Adapt for --without-threads

* Add second stress test

* Add NEWS blurb

* Address comments @haypo

* bpo-16500: Allow registering at-fork handlers

* Address Serhiy's comments

* Add doc for new C API

* Add doc for new Python-facing function

* Add NEWS entry + doc nit

Before, it was possible to get the following sequence of
events (especially on Windows, where the C-level signal handler for
SIGINT is run in a separate thread):

- SIGINT arrives
- trip_signal is called
- trip_signal writes to the wakeup fd
- the main thread wakes up from select()-or-equivalent
- the main thread checks for pending signals, but doesn't see any
- the main thread drains the wakeup fd
- the main thread goes back to sleep
- trip_signal sets is_tripped=1 and calls Py_AddPendingCall to notify
  the main thread the it should run the Python-level signal handler
- the main thread doesn't notice because it's asleep

This has been causing repeated failures in the Trio test suite:
  https://github.com/python-trio/trio/issues/119

* bpo-6532: Make the thread id an unsigned integer.

From C API side the type of results of PyThread_start_new_thread() and
PyThread_get_thread_ident(), the id parameter of
PyThreadState_SetAsyncExc(), and the thread_id field of PyThreadState
changed from "long" to "unsigned long".

* Restore a check in thread_get_ident().

Patch by Masayuki Yamamoto, reviewed and rebased by Erik Bray.

This is a first step on the long road toward resupporting Cygwin, which does
not provide siginfo_t.si_band.

Also update the classmethod and staticmethod doc strings and comments to
match the RST documentation.

The signal module was using old-style module initialization with
potential NULL dereferencing.

CID 1295026

generated by Argument Clinic.  Patch by Petr Viktorin.

in places where Py_DECREF was used.

macro Py_SETREF.

signalmodule.c

Retry:

* signal.sigtimedwait()
* threading.Lock.acquire()
* threading.RLock.acquire()
* time.sleep()

Add _Py_fstat_noraise() function when a Python exception is not welcome.

All these functions only accept positive timeouts, so this change has no effect
in practice.

* Add _PyTime_AsTimespec()
* Add unit tests for _PyTime_AsTimespec()

when interrupted by a signal not in the *sigset* parameter, if the signal
handler does not raise an exception. signal.sigtimedwait() recomputes the
timeout with a monotonic clock when it is retried.

Remove test_signal.test_sigwaitinfo_interrupted() because sigwaitinfo() doesn't
raise InterruptedError anymore if it is interrupted by a signal not in its
sigset parameter.

fstat() may fail with EOVERFLOW on files larger than 2 GB because the file size type is an signed 32-bit integer.

Detect integer overflow on the file descriptor of the socket on 64-bit Python.

- interpreter startup and shutdown code moved to a new
  pylifecycle.c module
- Py_OptimizeFlag moved into the new module with the other
  global flags

descriptor is in blocking mode.

A side effect is that Python depends to the WinSock library.

ValueError on fstat() failure.

aways from zero, instead of rounding towards zero.

It should make test_asyncio more reliable, especially test_timeout_rounding() test.

Issue #16105: When a signal handler fails to write to the file descriptor registered with ``signal.set_wakeup_fd()``, report an exception instead of ignoring the error.

PyStructSequence_InitType() except that it has a return value (0 on success,
-1 on error).

 * PyStructSequence_InitType2() now raises MemoryError on memory allocation failure
 * Fix also some calls to PyDict_SetItemString(): handle error

- Issue #17782: Fix undefined behaviour on platforms where ``struct timespec``'s "tv_nsec" member is not a C long.