[Python-checkins] bpo-31731: Fix test_io.check_interrupted_write() (GH-11225)

[Victor Stinner]

https://github.com/python/cpython/commit/05c9d31eb62cc45dc3c55a5cdb7cbc713d0421db
commit: 05c9d31eb62cc45dc3c55a5cdb7cbc713d0421db
branch: master
author: Victor Stinner <vstinner at redhat.com>
committer: GitHub <noreply at github.com>
date: 2018-12-18T23:52:39+01:00
summary:

bpo-31731: Fix test_io.check_interrupted_write() (GH-11225)

Fix a race condition in check_interrupted_write() of test_io:
create directly the thread with SIGALRM signal blocked,
rather than blocking the signal later from the thread. Previously, it
was possible that the thread gets the signal before the signal is
blocked.

files:
A Misc/NEWS.d/next/Tests/2018-12-18-23-20-39.bpo-31731.tcv85C.rst
M Lib/test/test_io.py

diff --git a/Lib/test/test_io.py b/Lib/test/test_io.py
index dc353c159fb0..c3644875103d 100644
--- a/Lib/test/test_io.py
+++ b/Lib/test/test_io.py
@@ -4149,10 +4149,9 @@ def check_interrupted_write(self, item, bytes, **fdopen_kwargs):
         in the latter."""
         read_results = []
         def _read():
-            if hasattr(signal, 'pthread_sigmask'):
-                signal.pthread_sigmask(signal.SIG_BLOCK, [signal.SIGALRM])
             s = os.read(r, 1)
             read_results.append(s)
+
         t = threading.Thread(target=_read)
         t.daemon = True
         r, w = os.pipe()
@@ -4160,7 +4159,14 @@ def _read():
         large_data = item * (support.PIPE_MAX_SIZE // len(item) + 1)
         try:
             wio = self.io.open(w, **fdopen_kwargs)
-            t.start()
+            if hasattr(signal, 'pthread_sigmask'):
+                # create the thread with SIGALRM signal blocked
+                signal.pthread_sigmask(signal.SIG_BLOCK, [signal.SIGALRM])
+                t.start()
+                signal.pthread_sigmask(signal.SIG_UNBLOCK, [signal.SIGALRM])
+            else:
+                t.start()
+
             # Fill the pipe enough that the write will be blocking.
             # It will be interrupted by the timer armed above.  Since the
             # other thread has read one byte, the low-level write will
diff --git a/Misc/NEWS.d/next/Tests/2018-12-18-23-20-39.bpo-31731.tcv85C.rst b/Misc/NEWS.d/next/Tests/2018-12-18-23-20-39.bpo-31731.tcv85C.rst
new file mode 100644
index 000000000000..530977c6e87e
--- /dev/null
+++ b/Misc/NEWS.d/next/Tests/2018-12-18-23-20-39.bpo-31731.tcv85C.rst
@@ -0,0 +1,4 @@
+Fix a race condition in ``check_interrupted_write()`` of test_io: create
+directly the thread with SIGALRM signal blocked, rather than blocking the
+signal later from the thread. Previously, it was possible that the thread gets
+the signal before the signal is blocked.