pythonbuf fix (#2675)

* Added test_thread testing for ostream_redirect segfault recreation

* fix: scoped_ostream_redirect str created outside gil

* Moved threading tests into test_iostream. Cleaned up some formatting. Deleted test_thread.{cpp,py}

* CI: few formatting fixes

* CI: yet another formatting fix

* CI: more formatting fixes. Removed unecessary comment

* Ignore 'warning C4702: unreachable code' in MSVC 2015

Co-authored-by: Nick Bridge <nick.bridge.chess@gmail.com>
Co-authored-by: Nick Bridge <nbridge@jumptrading.com>
Co-authored-by: Yannick Jadoul <yannick.jadoul@belgacom.net>

tests/test_iostream.py

@@ -216,3 +216,26 @@ def test_redirect_both(capfd):
     assert stderr == ""
     assert stream.getvalue() == msg
     assert stream2.getvalue() == msg2
+
+
+def test_threading():
+    with m.ostream_redirect(stdout=True, stderr=False):
+        # start some threads
+        threads = []
+
+        # start some threads
+        for _j in range(20):
+            threads.append(m.TestThread())
+
+        # give the threads some time to fail
+        threads[0].sleep()
+
+        # stop all the threads
+        for t in threads:
+            t.stop()
+
+        for t in threads:
+            t.join()
+
+        # if a thread segfaults, we don't get here
+        assert True