Merged revisions 86981,86984 via svnmerge from

svn+ssh://pythondev@svn.python.org/python/branches/py3k

........
  r86981 | antoine.pitrou | 2010-12-03 19:41:39 +0100 (ven., 03 déc. 2010) | 5 lines

  Issue #10478: Reentrant calls inside buffered IO objects (for example by
  way of a signal handler) now raise a RuntimeError instead of freezing the
  current process.
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  r86984 | antoine.pitrou | 2010-12-03 20:14:17 +0100 (ven., 03 déc. 2010) | 3 lines

  Add an "advanced topics" section to the io doc.
........

Lib/test/test_io.py

@@ -2561,12 +2561,50 @@ class SignalsTest(unittest.TestCase):
     def test_interrupted_write_text(self):
         self.check_interrupted_write("xy", b"xy", mode="w", encoding="ascii")
 
+    def check_reentrant_write(self, data, **fdopen_kwargs):
+        def on_alarm(*args):
+            # Will be called reentrantly from the same thread
+            wio.write(data)
+            1/0
+        signal.signal(signal.SIGALRM, on_alarm)
+        r, w = os.pipe()
+        wio = self.io.open(w, **fdopen_kwargs)
+        try:
+            signal.alarm(1)
+            # Either the reentrant call to wio.write() fails with RuntimeError,
+            # or the signal handler raises ZeroDivisionError.
+            with self.assertRaises((ZeroDivisionError, RuntimeError)) as cm:
+                while 1:
+                    for i in range(100):
+                        wio.write(data)
+                        wio.flush()
+                    # Make sure the buffer doesn't fill up and block further writes
+                    os.read(r, len(data) * 100)
+            exc = cm.exception
+            if isinstance(exc, RuntimeError):
+                self.assertTrue(str(exc).startswith("reentrant call"), str(exc))
+        finally:
+            wio.close()
+            os.close(r)
+
+    def test_reentrant_write_buffered(self):
+        self.check_reentrant_write(b"xy", mode="wb")
+
+    def test_reentrant_write_text(self):
+        self.check_reentrant_write("xy", mode="w", encoding="ascii")
+
+
 class CSignalsTest(SignalsTest):
     io = io
 
 class PySignalsTest(SignalsTest):
     io = pyio
 
+    # Handling reentrancy issues would slow down _pyio even more, so the
+    # tests are disabled.
+    test_reentrant_write_buffered = None
+    test_reentrant_write_text = None
+
 
 def test_main():
     tests = (CIOTest, PyIOTest,