[2.7] bpo-31334: Fix timeout in select.poll.poll() (GH-3277) (#4034)

Always pass -1, or INFTIM where defined, to the poll() system call when
a negative timeout is passed to the poll.poll([timeout]) method in the
select module. Various OSes throw an error with arbitrary negative
values..
(cherry picked from commit 6cfa927c)

Lib/test/test_poll.py

@@ -208,7 +208,7 @@ class PollTests(unittest.TestCase):
     @unittest.skipUnless(threading, 'Threading required for this test.')
     @reap_threads
     def test_poll_blocks_with_negative_ms(self):
-        for timeout_ms in [None, -1, -1.0]:
+        for timeout_ms in [None, -1000, -1, -1.0]:
             # Create two file descriptors. This will be used to unlock
             # the blocking call to poll.poll inside the thread
             r, w = os.pipe()

Misc/ACKS

@@ -262,6 +262,7 @@ Brad Clements
 Robbie Clemons
 Steve Clift
 Hervé Coatanhay
+Riccardo Coccioli
 Nick Coghlan
 Josh Cogliati
 Dave Cole

Misc/NEWS.d/next/Library/2017-09-04-00-22-31.bpo-31334.9WYRfi.rst

+Fix ``poll.poll([timeout])`` in the ``select`` module for arbitrary negative
+timeouts on all OSes where it can only be a non-negative integer or -1.
+Patch by Riccardo Coccioli.

Modules/selectmodule.c

@@ -530,6 +530,17 @@ poll_poll(pollObject *self, PyObject *args)
             return NULL;
     }
 
+    /* On some OSes, typically BSD-based ones, the timeout parameter of the
+       poll() syscall, when negative, must be exactly INFTIM, where defined,
+       or -1. See issue 31334. */
+    if (timeout < 0) {
+#ifdef INFTIM
+        timeout = INFTIM;
+#else
+        timeout = -1;
+#endif
+    }
+
     /* Avoid concurrent poll() invocation, issue 8865 */
     if (self->poll_running) {
         PyErr_SetString(PyExc_RuntimeError,