Add a basic synchronization mechanism to wait until the child process is ready
before sending it a signal.

Since Python 3.3, the C signal handler writes the signal number into the wakeup
file descriptor and then schedules the Python call using Py_AddPendingCall().

asyncio uses the wakeup file descriptor to wake up the event loop, and relies
on Py_AddPendingCall() to schedule the final callback with call_soon().

If the C signal handler is called in a thread different than the thread of the
event loop, the loop is awaken but Py_AddPendingCall() was not called yet. In
this case, the event loop has nothing to do and go to sleep again.
Py_AddPendingCall() is called while the event loop is sleeping again and so the
final callback is not scheduled immediatly.

This patch changes how asyncio handles signals. Instead of relying on
Py_AddPendingCall() and the wakeup file descriptor, asyncio now only relies on
the wakeup file descriptor. asyncio reads signal numbers from the wakeup file
descriptor to call its signal handler.

ConnectionResetError

ConnectionResetError too

If you want to handle the BrokenPipeError, you can easily reimplement
communicate().

Add also a unit test to ensure that stdin.write() + stdin.drain() raises
BrokenPipeError.

attribute.  Based on patch by Martin Panter.

pydoc.gui was removed over 3 years ago (#10818), this script has been
utterly bereft of worth since then.

in gather().

The _SelectorSslTransport constructor already calls it.

Fix regression that this test would have caught.

in debug mode

* Tulip issue #184: Log subprocess events in debug mode

  - Log stdin, stdout and stderr transports and protocols
  - Log process identifier (pid)
  - Log connection of pipes
  - Log process exit
  - Log Process.communicate() tasks: feed stdin, read stdout and stderr
  - Add __repr__() method to many classes related to subprocesses


* Add BaseSubprocessTransport._pid attribute. Store the pid so it is still
  accessible after the process exited. It's more convinient for debug.

* create_connection(): add the socket in the "connected to" debug log

* Clean up some docstrings and comments. Remove unused unimplemented
  _read_from_self().

test purposes are now reflected in GrepDialog and ReplaceDialog.  Docstrings
are improved. Initial patch by Saimadhav Heblikar

broken by the fix for security issue #19435.  Patch by Zach Byrne.

broken by the fix for security issue #19435.  Patch by Zach Byrne.

broken by the fix for security issue #19435.  Patch by Zach Byrne.

* Tulip issue #183: log socket events in debug mode

  - Log most important socket events: socket connected, new client, connection
    reset or closed by peer (EOF), etc.
  - Log time elapsed in DNS resolution (getaddrinfo)
  - Log pause/resume reading
  - Log time of SSL handshake
  - Log SSL handshake errors
  - Add a __repr__() method to many classes

* Fix ProactorEventLoop() in debug mode. ProactorEventLoop._make_self_pipe()
  doesn't call call_soon() directly because it checks for the current loop
  which fails, because the method is called to build the event loop.

* Cleanup _ProactorReadPipeTransport constructor. Not need to set again
  _read_fut attribute to None, it is already done in the base class.

- Fix the documentation of Server.close(): it closes sockets
- Replace AbstractServer with Server
- Document Server.sockets attribute

- loop, waiters and active_count attributes are now private
- attach(), detach() and wakeup() methods are now private

The sockets attribute remains public.

Patch by Zachary Ware.

* Tulip issue #182: Improve logs of BaseEventLoop._run_once()

  - Don't log non-blocking poll
  - Only log polling with a timeout if it gets events or if it timed out after
    more than 1 second.

* Fix some pyflakes warnings: remove unused imports

- CoroWrapper.__del__() now reuses repr(CoroWrapper) to log the "... was never
  yielded from" warning
- Improve CoroWrapper: copy also the qualified name on Python 3.4, not only on
  Python 3.5+

- repr(Task) and repr(CoroWrapper) now also includes where these objects were
  created. If the coroutine is not a generator (don't use "yield from"), use
  the location of the function, not the location of the coro() wrapper.
- Fix create_task(): truncate the traceback to hide the call to create_task().

- Issues #21936, #21163: Fix sporadic failures of
  test_future_exception_never_retrieved()
- Handle.cancel() now clears references to callback and args
- In debug mode, repr(Handle) now contains the location where the Handle was
  created.