mode.  Explicitly remove the PYTHONFAULTHANDLER environment variable before
launching a child interpreter when its presence would impact the test (the
reason -E was being used in the first place).

This enables running the test in an environment where other Python environment
variables must be set in order for things to run (such as using PYTHONHOME to
tell an embedded interpreter where it should think it lives).

because _read_null() cannot be used on AIX. On AIX, reading from NULL is
allowed: the first page of memory is a mapped read-only on AIX.

Patch written by Xavier de Gaye.

None: RuntimeError("sys.stderr is None") instead of AttributeError("'NoneType'
object has no attribute 'fileno'").

Issue #18948: improve SuppressCoreFiles to include Windows crash popup suppression, and use it in more tests.
Patch by Valerie Lambert and Zachary Ware.

faulthandler module if the variable is non-empty. Same behaviour than other
variables like PYTHONDONTWRITEBYTECODE.

AIX maps the first page of memory at address zero as valid, read-only.  Reading
NULL is not a fault on AIX. This is utilized by IBM compiler optimizations.
One speculatively can indirect through a pointer which may be null without
first testing if null and defer the test before using the value.

(test.regrtest and test.script_helper enable faulthandler module in
subprocesses).

faulthandler._read_null() is not reliable: it does not crash on AIX.

instead of manually listing tests for test.support.run_unittest().

dump_traceback_later() and cancel_dump_tracebacks_later() to
cancel_dump_traceback_later().

to 500 characters.

faulthandler requires the importlib if "-X faulthandler" option is present on
the command line, so initialize faulthandler after importlib.

Add also an unit test.

Closes #14729: Allowed test to pass on Windows by adjusting the test condition slightly to allow for a Windows-specific error message.

sigaltstack(2) doesn't work when linked with pthread.

Read from NULL raises SIGILL, not SIGSEGV, on Mac OS X Lion.

Call the previous signal handler if chain is True.

instead of open(os.devnull, 'w')

faulthandler.enable() requires that sys.stderr has a fileno() method.

_check_dump_tracebacks_later() to avoid failures if the system is slow.

 * Set the default value of all_threads arguments to True
 * Py_FatalError() dumps all threads, instead of only the current thread

Dump only the current thread is not reliable. In some cases, Python is unable
to retrieve the state of the current thread and so is unable to dump the
traceback. faulthandler keeps a reference to the interpreter and so is always
able to dump the traceback of all threads.

 * Write a new test to ensure that dump_tracebacks_later() still works if
   it was already called and then cancelled before
 * Don't use a variable to check the status of the thread, only rely on locks
 * The thread only releases cancel_event if it was able to acquire it (if
   the timer was interrupted)
 * The main thread always hold this lock. It is only released when
   faulthandler_thread() is interrupted until this thread exits, or at Python
   exit.

time.time() and/or time.sleep() are not accurate on Windows, don't test them
in test_faulthandler. Anyway, the check was written for an old implementation
of dump_tracebacks_later(), it is not more needed.

The traceback may contain "_is_owned":

Thread 0x40962b90:
  File "/srv/buildbot/buildarea/3.x.bolen-ubuntu/build/Lib/threading.py", line 220 in _is_owned
  File "/srv/buildbot/buildarea/3.x.bolen-ubuntu/build/Lib/threading.py", line 227 in wait
  File "/srv/buildbot/buildarea/3.x.bolen-ubuntu/build/Lib/threading.py", line 421 in wait
  File "<string>", line 23 in run
  File "/srv/buildbot/buildarea/3.x.bolen-ubuntu/build/Lib/threading.py", line 735 in _bootstrap_inner
  File "/srv/buildbot/buildarea/3.x.bolen-ubuntu/build/Lib/threading.py", line 708 in _bootstrap

Current thread XXX:
  File "<string>", line 10 in dump
  File "<string>", line 28 in <module>

 * faulthandler_user() displays the tracebacks of all threads even if it is
   unable to get the state of the current thread
 * test_faulthandler: only release the GIL in test_gil_released() check
 * create check_signum() subfunction

Stop if the stack overflow doesn't occur after allocating 100 MB on the stack.