Bugs item #1074011, was opened at 2004-11-26 23:02 Message generated for change (Comment added) made by meyering You can respond by visiting: https://sourceforge.net/tracker/?func=detail&atid=105470&aid=1074011&group_id=5470
Category: Python Interpreter Core Group: Python 2.3 Status: Open Resolution: None Priority: 6 Submitted By: Matthias Klose (doko) Assigned to: Nobody/Anonymous (nobody) Summary: write failure ignored in Py_Finalize() Initial Comment: [forwarded from http://bugs.debian.org/283108] Write errors on stdout may be ignored, and hence may result in loss of valuable user data. Here's a quick demo: $ ./close-bug foo $ ./close-bug > /dev/full && echo unreported write failure unreported write failure $ cat close-bug #!/usr/bin/python import sys def main (): try: print 'foo' sys.stdout.close () except IOError, e: sys.stderr.write ('write failed: %s\n' % e) sys.exit (1) if __name__ == '__main__': main () This particular failure comes from the following unchecked fflush of stdout in pythonrun.c: static void call_ll_exitfuncs(void) { while (nexitfuncs > 0) (*exitfuncs[--nexitfuncs])(); fflush(stdout); fflush(stderr); } Flushing the stream manually, python does raise an exception. Please note that simply adding a test for fflush failure is not sufficient. If you change the above to do this: if (fflush(stdout) != 0) { ...handle error... } It will appear to solve the problem. But here is a counterexample: import sys def main (): try: print "x" * 4095 print sys.stdout.close () except IOError, e: sys.stderr.write ('write failed: %s\n' % e) sys.exit (1) if __name__ == '__main__': main () If you run the above with stdout redirected to /dev/full, it will silently succeed (exit 0) in spite of a write failure. That's what happens on my debian unstable system. Instead of just checking the fflush return value, it should also check ferror: if (fflush(stdout) != 0 || ferror(stdout)) { ...handle error... } ---------------------------------------------------------------------- Comment By: Jim Meyering (meyering) Date: 2004-12-06 23:27 Message: Logged In: YES user_id=41497 Even with python-2.4 (built fresh from CVS this morning), I can still reproduce the problem on a Linux-2.6.9/ext3 system: /p/p/python-2.4/bin/python write-4096 > /dev/full && echo fail fail The size that provokes the failure depends on the I/O block size of your system, so you might need something as big as 131072 on some other type of system. ---------------------------------------------------------------------- Comment By: Ben Hutchings (wom-work) Date: 2004-12-06 23:11 Message: Logged In: YES user_id=203860 The second sample script works for me (in that it raises the expected exception) with or without my patch. If the error status of the file has been set by some other operation without Python noticing it then surely that's a bug in the code that calls that other operation. ---------------------------------------------------------------------- Comment By: Jim Meyering (meyering) Date: 2004-12-02 09:20 Message: Logged In: YES user_id=41497 Hi, I submitted the original report (and text above). The patch that just calls fflush is not enough, as the second sample script illustrates. Here's a patch that does a little better --- Python/sysmodule.c.~2.126.~ 2004-08-12 20:19:17.000000000 +0200 +++ Python/sysmodule.c 2004-12-02 09:59:09.058953816 +0100 @@ -927,6 +927,13 @@ settrace() -- set the global debug traci ) /* end of sys_doc */ ; +static int +_check_and_flush (FILE *stream) +{ + int prev_fail = ferror (stream); + return fflush (stream) || prev_fail ? EOF : 0; +} + PyObject * _PySys_Init(void) { @@ -941,8 +948,8 @@ _PySys_Init(void) sysdict = PyModule_GetDict(m); sysin = PyFile_FromFile(stdin, "<stdin>", "r", NULL); - sysout = PyFile_FromFile(stdout, "<stdout>", "w", NULL); - syserr = PyFile_FromFile(stderr, "<stderr>", "w", NULL); + sysout = PyFile_FromFile(stdout, "<stdout>", "w", _check_and_flush); + syserr = PyFile_FromFile(stderr, "<stderr>", "w", _check_and_flush); if (PyErr_Occurred()) return NULL; #ifdef MS_WINDOWS With that patch, the failing script now evokes a diagnostic and nonzero exit. $ ./python write-4096 > /dev/full write failed: (0, 'Error') But, as you can see, the diagnostic leaves a lot to be desired. It should say ``write failes: [Errno 28] No space left on device''. It'll take a more significant change to propagate errno from the failing fputs/fwrite/etc. to where it can be used. [EMAIL PROTECTED] ---------------------------------------------------------------------- Comment By: Ben Hutchings (wom-work) Date: 2004-11-29 10:51 Message: Logged In: YES user_id=203860 I can't see how to upload an attachment to this bug, so see patch 1075147. ---------------------------------------------------------------------- Comment By: Ben Hutchings (wom-work) Date: 2004-11-29 10:43 Message: Logged In: YES user_id=203860 Each Python file object has a pointer to the function to be called on the C stream when close is called on the file object. Normally this is fclose, but Python doesn't want the standard streams closed so their file objects are created with the function pointer set to NULL, making close a no-op on the underlying files. I'm going to attach a patch that changes the function for stdout and stderr to be fflush, so that the streams stay open but write errors are detected at the time of an explicit close. I don't see the relevance of the exitfuncs. ---------------------------------------------------------------------- You can respond by visiting: https://sourceforge.net/tracker/?func=detail&atid=105470&aid=1074011&group_id=5470 _______________________________________________ Python-bugs-list mailing list Unsubscribe: http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
