[Python-checkins] CVS: python/dist/src/Lib tempfile.py,1.34,1.34.4.1

[Michael Hudson]

Update of /cvsroot/python/python/dist/src/Lib
In directory usw-pr-cvs1:/tmp/cvs-serv13535

Modified Files:
      Tag: release22-maint
	tempfile.py 
Log Message:
So there is some merit in slogging through ~4800 lines of cvs log.

Bring tempfile.py up to date from the trunk.  There have been three 
checkins (all by Tim):

SF bug #509805 tempfile.gettempdir not threadsafe
This is an ancient race when multiple threads call gettempdir() (or
anything relying on it) for the first time.

Fixed x-platform via the Big Hammer of rearranging the code to serialize
the first calls.  Subsequent calls are as fast as before.

Note that the Python test suite can't provoke this bug:  it requires
setting up multiple threads making the very first calls into tempfile,
but the test suite uses tempfile several times before getting to
test_threadedtempfile.

Bugfix candidate.

[and]

New TemporaryFile implementation for Windows:  this doesn't need a
TemproraryFileWrapper wrapper anymore, and should be immune from the
problem that a temp file inherited by a spawned process caused an
attempt to close the temp file in the spawning process to blow
up (the unlink in TemporaryFileWrapper.close() blew up with a
"Permission denied" error because, despite that the temp file got
closed in the spawning process, the spawned process still had it open
by virtue of C-level file descriptor inheritance).  In context,
that bug took days to figure out <wink/sigh>.

[and]

Thanks to Detlef Lannert for pointing out a typo in the code that
uses _DummyMutex on platforms without threads.

The first and third of these are pretty clearly bugfixes; I think the 
second is too.



Index: tempfile.py
===================================================================
RCS file: /cvsroot/python/python/dist/src/Lib/tempfile.py,v
retrieving revision 1.34
retrieving revision 1.34.4.1
diff -C2 -d -r1.34 -r1.34.4.1
*** tempfile.py	18 Dec 2001 23:22:01 -0000	1.34
--- tempfile.py	17 Mar 2002 17:54:32 -0000	1.34.4.1
***************
*** 18,21 ****
--- 18,45 ----
      if tempdir is not None:
          return tempdir
+ 
+     # _gettempdir_inner deduces whether a candidate temp dir is usable by
+     # trying to create a file in it, and write to it.  If that succeeds,
+     # great, it closes the file and unlinks it.  There's a race, though:
+     # the *name* of the test file it tries is the same across all threads
+     # under most OSes (Linux is an exception), and letting multiple threads
+     # all try to open, write to, close, and unlink a single file can cause
+     # a variety of bogus errors (e.g., you cannot unlink a file under
+     # Windows if anyone has it open, and two threads cannot create the
+     # same file in O_EXCL mode under Unix).  The simplest cure is to serialize
+     # calls to _gettempdir_inner.  This isn't a real expense, because the
+     # first thread to succeed sets the global tempdir, and all subsequent
+     # calls to gettempdir() reuse that without trying _gettempdir_inner.
+     _tempdir_lock.acquire()
+     try:
+         return _gettempdir_inner()
+     finally:
+         _tempdir_lock.release()
+ 
+ def _gettempdir_inner():
+     """Function to calculate the directory to use."""
+     global tempdir
+     if tempdir is not None:
+         return tempdir
      try:
          pwd = os.getcwd()
***************
*** 170,175 ****
              os.close(fd)
              raise
      else:
!         # Non-unix -- can't unlink file that's still open, use wrapper
          file = open(name, mode, bufsize)
          return TemporaryFileWrapper(file, name)
--- 194,215 ----
              os.close(fd)
              raise
+     elif os.name == 'nt':
+         # Windows -- can't unlink an open file, but O_TEMPORARY creates a
+         # file that "deletes itself" when the last handle is closed.
+         # O_NOINHERIT ensures processes created via spawn() don't get a
+         # handle to this too.  That would be a security hole, and, on my
+         # Win98SE box, when an O_TEMPORARY file is inherited by a spawned
+         # process, the fd in the spawned process seems to lack the
+         # O_TEMPORARY flag, so the file doesn't go away by magic then if the
+         # spawning process closes it first.
+         flags = (os.O_RDWR | os.O_CREAT | os.O_EXCL |
+                  os.O_TEMPORARY | os.O_NOINHERIT)
+         if 'b' in mode:
+             flags |= os.O_BINARY
+         fd = os.open(name, flags, 0700)
+         return os.fdopen(fd, mode, bufsize)
      else:
!         # Assume we can't unlink a file that's still open, or arrange for
!         # an automagically self-deleting file -- use wrapper.
          file = open(name, mode, bufsize)
          return TemporaryFileWrapper(file, name)
***************
*** 180,185 ****
  # usually be a Python int, but if _counter.get_next() is called often
  # enough, it will become a Python long.
! # Note that the only name that survives this next block of code
! # is "_counter".
  
  class _ThreadSafeCounter:
--- 220,225 ----
  # usually be a Python int, but if _counter.get_next() is called often
  # enough, it will become a Python long.
! # Note that the only names that survive this next block of code
! # are "_counter" and "_tempdir_lock".
  
  class _ThreadSafeCounter:
***************
*** 210,217 ****
--- 250,259 ----
  
      _counter = _ThreadSafeCounter(_DummyMutex())
+     _tempdir_lock = _DummyMutex()
      del _DummyMutex
  
  else:
      _counter = _ThreadSafeCounter(thread.allocate_lock())
+     _tempdir_lock = thread.allocate_lock()
      del thread