* bpo-30765: Avoid blocking when PyThread_acquire_lock() is asked not to lock
This is especially important if PyThread_acquire_lock() is called reentrantly
(for example from a signal handler).
* Update 2017-06-26-14-29-50.bpo-30765.Q5iBmf.rst
* Avoid core logic when taking the mutex failed.
(cherry picked from commit f84ac420c2)
In Python 3.3, PyThread_set_key_value() did nothing if the key already exists
(if the current value is a non-NULL pointer).
When _PyGILState_NoteThreadState() is called twice on the same thread with a
different Python thread state, it still keeps the old Python thread state to
keep the old behaviour. Replacing the Python thread state with the new state
introduces new bugs: see issues #10915 and #15751.
the function did nothing if the key already exists (if the current value is a
non-NULL pointer).
_testcapi.run_in_subinterp() now correctly sets the new Python thread state of
the current thread when a subinterpreter is created.
* Don't create a thread at startup anymore to initialize the pthread library:
it changes the behaviour of many functions related to signal handling like
sigwait()
* Reenable test_sigtimedwait_poll() on FreeBSD 6
On FreeBSD6, pthread_kill() doesn't work on the main thread before the creation
of the first thread. Create therefore a dummy thread (no-op) a startup to
initialize the pthread library.
Add also a test for this use case, test written by Charles-François Natali.
