The file object readline() and readlines() methods can lose data when an underlying read system call is interrupted.  They will abort with an IOError in this case but any incomplete line data they have read will be discarded.

readline() and readlines() should never raise an IOError for the EINTR interrupted system call case.  They should handle that gracefully, retrying their reads after letting any Python signal handlers run.

3.x has the same issue.  unittest & patch forthcoming that addresses that as well.

2.6 also has the issue but it is in security fix only mode so I won't backport to that.

.readall() and the equivalent unbounded .read() also have this problem.

I haven't looked beyond the reading methods it is possible that some of the write implementations have a similar issue.  Patch gps02 for 3.2 attached.

I'll use that as the basis for a stand alone test_file_eintr.py targeted at 2.7.

I'm not sure why you're creating a separate test file. There are already signals-related tests in test_io. Also, perhaps you can reuse the idioms used there, rather than spawn subprocesses.

New changeset 781b95159954 by Gregory P. Smith in branch '3.2':
Fixes issue #12268: File readline, readlines and read() or readall() methods
http://hg.python.org/cpython/rev/781b95159954

New changeset 19a6bef57490 by Gregory P. Smith in branch 'default':
Fixes issue #12268: File readline, readlines and read() or readall() methods
http://hg.python.org/cpython/rev/19a6bef57490

I'm leaving this open as I still need to audit the write methods and commit the fix(es) for 2.7.

I tried to merge the test into test_io's signals tests but I could not get that to actually work to reproduce the original problem so I kept my process based test_file_eintr one which easily reproduces it prior to these patches being applied instead.

For the record, there was a crash on the ARM buildbot:


[196/368/1] test_io
Timeout (1:00:00)!
Thread 0x2aac5300:
  File "/var/lib/buildbot/buildarea/3.x.warsaw-ubuntu-arm/build/Lib/test/test_io.py", line 3051 in check_interrupted_write_retry
  File "/var/lib/buildbot/buildarea/3.x.warsaw-ubuntu-arm/build/Lib/test/test_io.py", line 3073 in test_interrupted_write_retry_text
  File "/var/lib/buildbot/buildarea/3.x.warsaw-ubuntu-arm/build/Lib/unittest/case.py", line 385 in _executeTestPart
  File "/var/lib/buildbot/buildarea/3.x.warsaw-ubuntu-arm/build/Lib/unittest/case.py", line 440 in run
  File "/var/lib/buildbot/buildarea/3.x.warsaw-ubuntu-arm/build/Lib/unittest/case.py", line 492 in __call__
  File "/var/lib/buildbot/buildarea/3.x.warsaw-ubuntu-arm/build/Lib/unittest/suite.py", line 105 in run
  File "/var/lib/buildbot/buildarea/3.x.warsaw-ubuntu-arm/build/Lib/unittest/suite.py", line 67 in __call__
  File "/var/lib/buildbot/buildarea/3.x.warsaw-ubuntu-arm/build/Lib/unittest/suite.py", line 105 in run
  File "/var/lib/buildbot/buildarea/3.x.warsaw-ubuntu-arm/build/Lib/unittest/suite.py", line 67 in __call__
  File "/var/lib/buildbot/buildarea/3.x.warsaw-ubuntu-arm/build/Lib/unittest/runner.py", line 168 in run
  File "/var/lib/buildbot/buildarea/3.x.warsaw-ubuntu-arm/build/Lib/test/support.py", line 1383 in _run_suite
  File "/var/lib/buildbot/buildarea/3.x.warsaw-ubuntu-arm/build/Lib/test/support.py", line 1417 in run_unittest
  File "/var/lib/buildbot/buildarea/3.x.warsaw-ubuntu-arm/build/Lib/test/test_io.py", line 3121 in test_main
  File "/var/lib/buildbot/buildarea/3.x.warsaw-ubuntu-arm/build/Lib/test/regrtest.py", line 1194 in runtest_inner
  File "/var/lib/buildbot/buildarea/3.x.warsaw-ubuntu-arm/build/Lib/test/regrtest.py", line 905 in runtest
  File "/var/lib/buildbot/buildarea/3.x.warsaw-ubuntu-arm/build/Lib/test/regrtest.py", line 708 in main
  File "/var/lib/buildbot/buildarea/3.x.warsaw-ubuntu-arm/build/Lib/test/__main__.py", line 13 in <module>
  File "/var/lib/buildbot/buildarea/3.x.warsaw-ubuntu-arm/build/Lib/runpy.py", line 75 in _run_code
  File "/var/lib/buildbot/buildarea/3.x.warsaw-ubuntu-arm/build/Lib/runpy.py", line 162 in _run_module_as_main
make: *** [buildbottest] Error 1

I'm attaching an updated patch for 2.7.  It fixes read, readline, readlines and readinto and includes tests.

More code auditing for other methods to fix is still needed.

The 3.* ubuntu arm buildbot hanging in test_io is very odd.

I'm going to undo my supposedly straight forward signal.alarm(...) to signal.setitimer(...) change first to see if that is related.

New changeset 95b071194ddd by Gregory P. Smith in branch '3.2':
Backout change e8f44ebacda7052267318cecf5b6f128d35add17.  Reverting the test
http://hg.python.org/cpython/rev/95b071194ddd

New changeset b4ae7aa21b46 by Gregory P. Smith in branch 'default':
Backout change e8f44ebacda7052267318cecf5b6f128d35add17.  Reverting the test
http://hg.python.org/cpython/rev/b4ae7aa21b46

I don't think setitimer() is the culprit, rather the fact that the timeout is too short. You could try setting it to e.g. 0.4.

New changeset 67dc99a989cd by Gregory P. Smith in branch '2.7':
Fixes issue #12268 for file readline, readlines and read() and readinto methods.
http://hg.python.org/cpython/rev/67dc99a989cd

The uses of fwrite() and fflush() also need this EINTR treatment in 2.7.  I haven't checked the write paths in 3.2 yet.

Also, the fix change to 3.2's _io module needs backporting to 2.7's _io module for people using that.

New changeset 751a91e332d9 by Gregory P. Smith in branch '2.7':
Fixes Issue #12268 for the io module - File readline, readlines and
http://hg.python.org/cpython/rev/751a91e332d9

Is there anything left to do here?

Yes. See my comment from June. The write paths need to be taken care of.

Well, this issue is about "readline, readlines & readall". It would be easier to follow if you opened a separate issue.

New changeset a5e7b38caee2 by Gregory P. Smith in branch '2.7':
Additional fix for Issue #12268: The io module file object writelines() methods
http://hg.python.org/cpython/rev/a5e7b38caee2

New changeset 2fd669aa4abc by Gregory P. Smith in branch '3.2':
Additional fix for Issue #12268: The io module file object writelines() methods no longer abort early when one of its write system calls is interrupted (EINTR).
http://hg.python.org/cpython/rev/2fd669aa4abc

New changeset 30fc620e240e by Gregory P. Smith in branch '3.3':
Additional fix for issue #12268: The io module file object write methods no
http://hg.python.org/cpython/rev/30fc620e240e

New changeset 8f72519fd0e9 by Gregory P. Smith in branch 'default':
Additional fix for issue #12268: The io module file object write methods no
http://hg.python.org/cpython/rev/8f72519fd0e9

Oh, so we can now implement a version of writelines() using writev()!

2013/2/1 Roundup Robot <report@bugs.python.org>:
>
> Roundup Robot added the comment:
>
> New changeset a5e7b38caee2 by Gregory P. Smith in branch '2.7':
> Additional fix for Issue #12268: The io module file object writelines() methods
> http://hg.python.org/cpython/rev/a5e7b38caee2
>
> New changeset 2fd669aa4abc by Gregory P. Smith in branch '3.2':
> Additional fix for Issue #12268: The io module file object writelines() methods no longer abort early when one of its write system calls is interrupted (EINTR).
> http://hg.python.org/cpython/rev/2fd669aa4abc
>
> New changeset 30fc620e240e by Gregory P. Smith in branch '3.3':
> Additional fix for issue #12268: The io module file object write methods no
> http://hg.python.org/cpython/rev/30fc620e240e
>
> New changeset 8f72519fd0e9 by Gregory P. Smith in branch 'default':
> Additional fix for issue #12268: The io module file object write methods no
> http://hg.python.org/cpython/rev/8f72519fd0e9
>
> ----------
>
> _______________________________________
> Python tracker <report@bugs.python.org>
> <http://bugs.python.org/issue12268>
> _______________________________________

it was easier to just take care of auditing the write calls as part of this given the code change was directly related to it.

On Python 2.7 most of the write calls in the builtin file object (Objects/fileobject.c) rather than the new io module use the libc fwrite() call which, in linux man pages at least, is non-specific about what happens on EINTR (does it retry internally or does it return the number of bytes written so far?).  Those could well abort leading to an error.

Setting up a testcase fo to confirm that with is painful (time consuming) so I can't claim the non io module based write's do not still have an EINTR issue on 2.7.

Workaround: Use the io module instead of the builtin open() or file() calls in Python 2.7.

If someone can confirm that with a test case, it'd make another good issue to open.

As for the writev comment... go ahead. :)

Follow-up bug, readahead was missed: http://bugs.python.org/issue1633941