Make file objects as thread safe as the underlying libc FILE* implementation.

close() will now raise an IOError if any operations on the file object
are currently in progress in other threads.

Most code was written by Antoine Pitrou (pitrou).  Additional testing,
documentation and test suite cleanup done by me (gregory.p.smith).

Fixes issue 815646 and 595601 (as well as many other bugs and
references to this problem dating back to the dawn of Python).

Lib/test/test_file.py

@@ -1,9 +1,13 @@
 import sys
 import os
 import unittest
+import itertools
+import time
+import threading
 from array import array
 from weakref import proxy
 
+from test import test_support
 from test.test_support import TESTFN, findfile, run_unittest
 from UserList import UserList
 
@@ -339,11 +343,173 @@ def close(self):
         self.failUnless(f.subclass_closed)
 
 
+class FileThreadingTests(unittest.TestCase):
+    # These tests check the ability to call various methods of file objects
+    # (including close()) concurrently without crashing the Python interpreter.
+    # See #815646, #595601
+
+    def setUp(self):
+        self.f = None
+        self.filename = TESTFN
+        with open(self.filename, "w") as f:
+            f.write("\n".join("0123456789"))
+        self._count_lock = threading.Lock()
+        self.close_count = 0
+        self.close_success_count = 0
+
+    def tearDown(self):
+        if self.f:
+            try:
+                self.f.close()
+            except (EnvironmentError, ValueError):
+                pass
+        try:
+            os.remove(self.filename)
+        except EnvironmentError:
+            pass
+
+    def _create_file(self):
+        self.f = open(self.filename, "w+")
+
+    def _close_file(self):
+        with self._count_lock:
+            self.close_count += 1
+        self.f.close()
+        with self._count_lock:
+            self.close_success_count += 1
+
+    def _close_and_reopen_file(self):
+        self._close_file()
+        # if close raises an exception thats fine, self.f remains valid so
+        # we don't need to reopen.
+        self._create_file()
+
+    def _run_workers(self, func, nb_workers, duration=0.2):
+        with self._count_lock:
+            self.close_count = 0
+            self.close_success_count = 0
+        self.do_continue = True
+        threads = []
+        try:
+            for i in range(nb_workers):
+                t = threading.Thread(target=func)
+                t.start()
+                threads.append(t)
+            for _ in xrange(100):
+                time.sleep(duration/100)
+                with self._count_lock:
+                    if self.close_count-self.close_success_count > nb_workers+1:
+                        if test_support.verbose:
+                            print 'Q',
+                        break
+            time.sleep(duration)
+        finally:
+            self.do_continue = False
+            for t in threads:
+                t.join()
+
+    def _test_close_open_io(self, io_func, nb_workers=5):
+        def worker():
+            self._create_file()
+            funcs = itertools.cycle((
+                lambda: io_func(),
+                lambda: self._close_and_reopen_file(),
+            ))
+            for f in funcs:
+                if not self.do_continue:
+                    break
+                try:
+                    f()
+                except (IOError, ValueError):
+                    pass
+        self._run_workers(worker, nb_workers)
+        if test_support.verbose:
+            # Useful verbose statistics when tuning this test to take
+            # less time to run but still ensuring that its still useful.
+            #
+            # the percent of close calls that raised an error
+            percent = 100. - 100.*self.close_success_count/self.close_count
+            print self.close_count, ('%.4f ' % percent),
+
+    def test_close_open(self):
+        def io_func():
+            pass
+        self._test_close_open_io(io_func)
+
+    def test_close_open_flush(self):
+        def io_func():
+            self.f.flush()
+        self._test_close_open_io(io_func)
+
+    def test_close_open_iter(self):
+        def io_func():
+            list(iter(self.f))
+        self._test_close_open_io(io_func)
+
+    def test_close_open_isatty(self):
+        def io_func():
+            self.f.isatty()
+        self._test_close_open_io(io_func)
+
+    def test_close_open_print(self):
+        def io_func():
+            print >> self.f, ''
+        self._test_close_open_io(io_func)
+
+    def test_close_open_read(self):
+        def io_func():
+            self.f.read(0)
+        self._test_close_open_io(io_func)
+
+    def test_close_open_readinto(self):
+        def io_func():
+            a = array('c', 'xxxxx')
+            self.f.readinto(a)
+        self._test_close_open_io(io_func)
+
+    def test_close_open_readline(self):
+        def io_func():
+            self.f.readline()
+        self._test_close_open_io(io_func)
+
+    def test_close_open_readlines(self):
+        def io_func():
+            self.f.readlines()
+        self._test_close_open_io(io_func)
+
+    def test_close_open_seek(self):
+        def io_func():
+            self.f.seek(0, 0)
+        self._test_close_open_io(io_func)
+
+    def test_close_open_tell(self):
+        def io_func():
+            self.f.tell()
+        self._test_close_open_io(io_func)
+
+    def test_close_open_truncate(self):
+        def io_func():
+            self.f.truncate()
+        self._test_close_open_io(io_func)
+
+    def test_close_open_write(self):
+        def io_func():
+            self.f.write('')
+        self._test_close_open_io(io_func)
+
+    def test_close_open_writelines(self):
+        def io_func():
+            self.f.writelines('')
+        self._test_close_open_io(io_func)
+
+
+
 def test_main():
     # Historically, these tests have been sloppy about removing TESTFN.
     # So get rid of it no matter what.
     try:
-        run_unittest(AutoFileTests, OtherFileTests, FileSubclassTests)
+        run_unittest(AutoFileTests, OtherFileTests, FileSubclassTests,
+            FileThreadingTests)
     finally:
         if os.path.exists(TESTFN):
             os.unlink(TESTFN)