[lldb-dev] Too many open files

Todd Fiala via lldb-dev lldb-dev at lists.llvm.org
Fri Oct 9 20:05:57 PDT 2015 

Oh good!  I'm glad you found the root cause.

Later I anticipate the following will happen, which may help:
* the test event system is arranged to capture stdout/stderr from each test
method within the test events.
* the stdout/stderr from the inferior dotest.py will become far less
important and thus may no longer need pipes (really might not need to be
captured at all).

In that case, we might be able to cut down significantly on the number of
open handles.  I'm not too close to working on that yet but it's something
I'm planning to look at mid-term.

On Wed, Oct 7, 2015 at 3:57 PM, Adrian McCarthy <amccarth at google.com> wrote:

> Zach had the clue that found the problem.  Python on Windows uses the
> stdio from CRT.  On Windows, the default limit for open file descriptors is
> 512.  When you have 40 logical cores and the parent process spends several
> FDs communicating with each one, you get real close to that number.
>
> https://msdn.microsoft.com/en-us/library/6e3b887c.aspx
>
> As a test, I hacked a _setmaxstdio(2048) into the main() of my local copy
> of Python, and the problem went away.
>
> I guess the general solution is to limit the number of processes on
> Windows, which we already knew was a possible workaround.
>
>
> On Wed, Oct 7, 2015 at 3:17 PM, Adrian McCarthy <amccarth at google.com>
> wrote:
>
>> Adding a printing destructor to threading.Event seems to aggravate timing
>> problems, causing several tests to fail to make their inferiors and that
>> seemingly keeps us below the open file limit.  That aside, the destructor
>> did fire many hundreds of times, so there's not a general problem stopping
>> all or even most of those to be cleaned up.
>>
>> The event objects that I'm seeing with the Sysinternals tools are likely
>> Windows Events that Python creates to facilitate the interprocess
>> communication.
>>
>> I'm looking at the ProcessDriver lifetimes now.
>>
>> On Tue, Oct 6, 2015 at 9:54 AM, Todd Fiala <todd.fiala at gmail.com> wrote:
>>
>>> Okay.
>>>
>>> A promising avenue might be to look at how Windows cleans up the
>>> threading.Event objects.  Chasing that thread might yield why the events
>>> are not going away (assuming those are the events that are lingering on
>>> your end).  One thing you could consider doing is patching in a replacement
>>> destructor for the threading.Event and print something when it fires off,
>>> verifying that they're really going away from the Python side.  If they're
>>> not, perhaps there's a retain bloat issue where we're not getting rid of
>>> some python objects due to some unintended references living beyond
>>> expectations.
>>>
>>> The dosep.py call_with_timeout method drives the child process operation
>>> chain.  That thing creates a ProcessDriver and collects the results from it
>>> when done.  Everything within the ProcessDriver (including the event)
>>> should be cleaned up by the time the call_with_timeout() call wraps up as
>>> there shouldn't be any references outstanding.  It might also be worth you
>>> adding a destructor to the ProcessDriver to make sure that's going away,
>>> one per Python test inferior executed.
>>>
>>> On Tue, Oct 6, 2015 at 9:48 AM, Adrian McCarthy <amccarth at google.com>
>>> wrote:
>>>
>>>> Python 2.7.10 made no difference.  I'm dealing with other issues this
>>>> afternoon, so I'll probably return to this on Wednesday.  It's not critical
>>>> since there are workarounds.
>>>>
>>>> On Tue, Oct 6, 2015 at 9:41 AM, Todd Fiala <todd.fiala at gmail.com>
>>>> wrote:
>>>>
>>>>>
>>>>>
>>>>> On Mon, Oct 5, 2015 at 3:58 PM, Adrian McCarthy <amccarth at google.com>
>>>>> wrote:
>>>>>
>>>>>> Different tools are giving me different numbers.
>>>>>>
>>>>>> At the time of the error, Windbg says there are about 2000 open
>>>>>> handles, most of them are Event handles, not File handles.  That's higher
>>>>>> than I'd expect, but not really concerning.
>>>>>>
>>>>>>
>>>>> Ah, that's useful.  I am using events (python threading.Event).  These
>>>>> don't afford any clean up mechanisms on them, so I assume these go away
>>>>> when the Python objects that hold them go away.
>>>>>
>>>>>
>>>>>> Process Explorer, however, shows ~20k open handles per Python process
>>>>>> running dotest.exe.  It also says that about 2000 of those are the
>>>>>> process's "own handles."  I'm researching to see what that means.  I
>>>>>> suspect it means that the process has about ~18k handles to objects owned
>>>>>> by another process and 2k of ones that it actually owns.
>>>>>>
>>>>>> I found this Stack Overflow post, which suggests is may be an
>>>>>> interaction with using Python subprocess in a loop and having those
>>>>>> subprocesses work with files that are still open in the parent process, but
>>>>>> I don't entirely understand the answer:
>>>>>>
>>>>>>
>>>>>> http://stackoverflow.com/questions/16526783/python-subprocess-too-many-open-files
>>>>>>
>>>>>>
>>>>> Hmm I'll read through that.
>>>>>
>>>>>
>>>>>> It might be a problem with Python subprocess that's been fixed in a
>>>>>> newer version.  I'm going to try upgrading from Python 2.7.9 to 2.7.10 to
>>>>>> see if that makes a difference.
>>>>>>
>>>>>>
>>>>> Okay, we're on 2.7.10 on latest OS X.  I *think* I'm using Python
>>>>> 2.7.6 on Ubuntu 14.04.  Checking now... (yes, 2.7.6 on 14.04).  Ubuntu
>>>>> 15.10 beta 1 is using Python 2.7.10.
>>>>>
>>>>> Seems reasonable to check that out.  Let me know what you find out!
>>>>>
>>>>> -Todd
>>>>>
>>>>>
>>>>>> On Mon, Oct 5, 2015 at 12:02 PM, Todd Fiala <todd.fiala at gmail.com>
>>>>>> wrote:
>>>>>>
>>>>>>> It's possible.  However, I was monitoring actual open files during
>>>>>>> the course of the run (i.e. what the kernel thought was open for the master
>>>>>>> driver process, which is the only place that makes sense to see leaks
>>>>>>> accumulate) in both threading and threading-pool (on OS X), and I saw only
>>>>>>> the handful of file handles that I'd expect to  be open - pipes
>>>>>>> (stdout,stderr,stdin) from the main test runner to the inferior test
>>>>>>> runners, the shared libraries loaded as part of the test runner, and (in my
>>>>>>> case, but probably not yours for the configuration), the tcp sockets for
>>>>>>> gathering the test events.  There was no growth, and I didn't see things
>>>>>>> hanging around longer than I'd expect.
>>>>>>>
>>>>>>> The SysInternals process viewer tool is great for this kind of thing
>>>>>>> - glad you're using it.  Once you find out which file handles are getting
>>>>>>> leaked and where they came from, we can probably figure out which part of
>>>>>>> the implementation is leaking it.  I don't *expect* it to be on our side
>>>>>>> given that it's not showing up on a POSIX-y system, but maybe it really is
>>>>>>> but isn't in the form of a file handle on the POSIX side.  I should have a
>>>>>>> look at the memory growth...
>>>>>>>
>>>>>>> On Mon, Oct 5, 2015 at 11:41 AM, Adrian McCarthy <
>>>>>>> amccarth at google.com> wrote:
>>>>>>>
>>>>>>>> I'm poking around with some SysInternals tools.  Over the course of
>>>>>>>> test run, there are about 602k opens (CreateFiles) and 405k
>>>>>>>> closes (CloseFiles) system-wide.
>>>>>>>>
>>>>>>>> I'm looking for a way to stop it once the error happens, so I can
>>>>>>>> see how many files each process has open.  As it stands, the OS cleans up
>>>>>>>> once the error is hit.
>>>>>>>>
>>>>>>>> I wonder if it's not a matter of actually leaking open file handles
>>>>>>>> but that the closes are happening too late so that we cross the threshold
>>>>>>>> shortly before the test runner would have shut everything down.
>>>>>>>>
>>>>>>>> On Mon, Oct 5, 2015 at 11:32 AM, Todd Fiala <todd.fiala at gmail.com>
>>>>>>>> wrote:
>>>>>>>>
>>>>>>>>> On OS X, I'm also not seeing growth in the --test-runner-name
>>>>>>>>> threading-pool (the one you were using on Windows).
>>>>>>>>>
>>>>>>>>> Perhaps you can dig into if you're experiencing some kind of file
>>>>>>>>> leak on Windows.  It's possible you're hitting a platform-specific leak?  I
>>>>>>>>> recall Ed Maste hitting a FreeBSD-only leak in one or more of the python
>>>>>>>>> 2.7.x releases.
>>>>>>>>>
>>>>>>>>> On Mon, Oct 5, 2015 at 11:26 AM, Todd Fiala <todd.fiala at gmail.com>
>>>>>>>>> wrote:
>>>>>>>>>
>>>>>>>>>> Hmm, on OS X the file handles seem to be well behaved on the
>>>>>>>>>> --test-runner-name threading.  I'm not seeing any file handle growth beyond
>>>>>>>>>> the file handles I expect to be open.
>>>>>>>>>>
>>>>>>>>>> I'll see if the threading-pool behaves differently.  (That is
>>>>>>>>>> similar to threading but uses the multiprocessing.pool mechanism, at the
>>>>>>>>>> expense of me not  being able to catch Ctrl-C at all).
>>>>>>>>>>
>>>>>>>>>> It's possible the pool is introducing some leakage at the file
>>>>>>>>>> level.
>>>>>>>>>>
>>>>>>>>>> On Mon, Oct 5, 2015 at 11:20 AM, Todd Fiala <todd.fiala at gmail.com
>>>>>>>>>> > wrote:
>>>>>>>>>>
>>>>>>>>>>> Interesting, okay..
>>>>>>>>>>>
>>>>>>>>>>> This does appear to be an accumulation issue.  You made it most
>>>>>>>>>>> of the way through before the issue hit.  I suspect we're leaking file
>>>>>>>>>>> handles.  It probably doesn't hit the per-process limit on multiprocessing
>>>>>>>>>>> because the leaked files get spread across more processes.
>>>>>>>>>>>
>>>>>>>>>>> (All speculation but does fit the results).
>>>>>>>>>>>
>>>>>>>>>>> I'll see if I can look into what's there - if we've got an
>>>>>>>>>>> obvious leak, I'll take care of it.
>>>>>>>>>>>
>>>>>>>>>>> On Mon, Oct 5, 2015 at 9:58 AM, Adrian McCarthy <
>>>>>>>>>>> amccarth at google.com> wrote:
>>>>>>>>>>>
>>>>>>>>>>>> Thanks for the ideas.
>>>>>>>>>>>>
>>>>>>>>>>>> With `--test-runner-name threading-pool`, I get too many open
>>>>>>>>>>>> files.
>>>>>>>>>>>>
>>>>>>>>>>>> With `--test-runner-name multiprocessing-pool`, the suite runs
>>>>>>>>>>>> fine.
>>>>>>>>>>>>
>>>>>>>>>>>> My machine has 40 logical cores.
>>>>>>>>>>>>
>>>>>>>>>>>> With `--threads=20`:  SUCCESS (and perhaps _faster_).
>>>>>>>>>>>>
>>>>>>>>>>>> With `--threads=30`:  SUCCESS.
>>>>>>>>>>>>
>>>>>>>>>>>> With `--threads=36`:  SUCCESS.
>>>>>>>>>>>>
>>>>>>>>>>>> With `--threads=38`:  TOO MANY OPEN FILES.
>>>>>>>>>>>>
>>>>>>>>>>>> So we're right at the edge.  I'll keep investigating.
>>>>>>>>>>>>
>>>>>>>>>>>> So it seems we're on the bleeding edge.
>>>>>>>>>>>>
>>>>>>>>>>>>
>>>>>>>>>>>> On Fri, Oct 2, 2015 at 5:38 PM, Todd Fiala <
>>>>>>>>>>>> todd.fiala at gmail.com> wrote:
>>>>>>>>>>>>
>>>>>>>>>>>>> (swapped out the lldb list for the newer one)
>>>>>>>>>>>>>
>>>>>>>>>>>>> On Fri, Oct 2, 2015 at 5:37 PM, Todd Fiala <
>>>>>>>>>>>>> todd.fiala at gmail.com> wrote:
>>>>>>>>>>>>>
>>>>>>>>>>>>>> Hmm, sounds suspicious.
>>>>>>>>>>>>>>
>>>>>>>>>>>>>> Can you try running the tests with two options and see if you
>>>>>>>>>>>>>> get different results?
>>>>>>>>>>>>>>
>>>>>>>>>>>>>> # should be equivalent for the default on Windows, thus
>>>>>>>>>>>>>> should match your above results.  This one uses a thread per worker queue.
>>>>>>>>>>>>>> --test-runner-name threading-pool
>>>>>>>>>>>>>>
>>>>>>>>>>>>>> # should use a different test runner.  This one uses a
>>>>>>>>>>>>>> process per worker queue.
>>>>>>>>>>>>>> --test-runner-name multiprocessing-pool
>>>>>>>>>>>>>>
>>>>>>>>>>>>>> Aside from that, it seems like the total number of open files
>>>>>>>>>>>>>> is exceeding some process/system maximum, which sounds like (maybe) we're
>>>>>>>>>>>>>> leaking files somewhere.  Not enough info yet to guess where that might be
>>>>>>>>>>>>>> coming in from, but maybe a part of the test runner isn't closing files
>>>>>>>>>>>>>> somewhere.
>>>>>>>>>>>>>>
>>>>>>>>>>>>>> The other thing you can try is reducing the total number of
>>>>>>>>>>>>>> threads, with:
>>>>>>>>>>>>>> --threads
>>>>>>>>>>>>>> {some-number-lower-than-your-total-number-of-logical-cores}
>>>>>>>>>>>>>>
>>>>>>>>>>>>>> in the event that your machine has a mongo number of logical
>>>>>>>>>>>>>> cores, and perhaps it is trying to do too much.  (In that case, the
>>>>>>>>>>>>>> multiprocessing-pool runner might actually help).
>>>>>>>>>>>>>>
>>>>>>>>>>>>>> Thanks!
>>>>>>>>>>>>>>
>>>>>>>>>>>>>> -Todd
>>>>>>>>>>>>>>
>>>>>>>>>>>>>> On Fri, Oct 2, 2015 at 5:31 PM, Adrian McCarthy <
>>>>>>>>>>>>>> amccarth at google.com> wrote:
>>>>>>>>>>>>>>
>>>>>>>>>>>>>>> When running LLDB tests on Windows, I started getting a "too
>>>>>>>>>>>>>>> many open files" error from Python.  I used git bisect to narrow it down to
>>>>>>>>>>>>>>> this revision:
>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>> http://llvm.org/viewvc/llvm-project?view=revision&revision=249182
>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>> The error output is:
>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>> Command invoked: D:\src\Python-2.7.9\PCbuild\python_d.exe
>>>>>>>>>>>>>>> D:\src\llvm\llvm\tools\lldb\test\dotest.py -q --arch=i686 --executable
>>>>>>>>>>>>>>> D:/src/llvm/build/ninja/bin/lldb.exe -s
>>>>>>>>>>>>>>> D:/src/llvm/build/ninja/lldb-test-traces -u CXXFLAGS -u CFLAGS
>>>>>>>>>>>>>>> --enable-crash-dialog -C D:\src\llvm\build\ninja_release\bin\clang.exe
>>>>>>>>>>>>>>> --inferior -p TestRecursiveTypes.py D:\src\llvm\llvm\tools\lldb\test
>>>>>>>>>>>>>>> --event-add-entries worker_index=7:int
>>>>>>>>>>>>>>> 384 out of 400 test suites processed - TestRecursiveTypes.py
>>>>>>>>>>>>>>>                   Traceback (most recent call last):
>>>>>>>>>>>>>>>   File "D:/src/llvm/llvm/tools/lldb/test/dotest.py", line
>>>>>>>>>>>>>>> 1457, in <module>
>>>>>>>>>>>>>>>   File "D:\src\llvm\llvm\tools\lldb\test\dosep.py", line
>>>>>>>>>>>>>>> 1355, in main
>>>>>>>>>>>>>>>   File "D:\src\llvm\llvm\tools\lldb\test\dosep.py", line
>>>>>>>>>>>>>>> 968, in walk_and_invoke
>>>>>>>>>>>>>>>   File "D:\src\llvm\llvm\tools\lldb\test\dosep.py", line
>>>>>>>>>>>>>>> 1095, in <lambda>
>>>>>>>>>>>>>>>   File "D:\src\llvm\llvm\tools\lldb\test\dosep.py", line
>>>>>>>>>>>>>>> 889, in threading_test_runner_pool
>>>>>>>>>>>>>>>   File "D:\src\llvm\llvm\tools\lldb\test\dosep.py", line
>>>>>>>>>>>>>>> 774, in map_async_run_loop
>>>>>>>>>>>>>>>   File "D:\src\Python-2.7.9\Lib\multiprocessing\pool.py",
>>>>>>>>>>>>>>> line 558, in get
>>>>>>>>>>>>>>> OSError: [Errno 24] Too many open files
>>>>>>>>>>>>>>> [77809 refs]
>>>>>>>>>>>>>>> ninja: build stopped: subcommand failed.
>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>> Any clue what might have caused this or what can be done to
>>>>>>>>>>>>>>> fix it?
>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>> It's Friday afternoon, so there's no urgency from my
>>>>>>>>>>>>>>> perspective.  I'll probably get back to this on Monday morning.
>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>> Thanks,
>>>>>>>>>>>>>>> Adrian McCarthy
>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>
>>>>>>>>>>>>>>
>>>>>>>>>>>>>>
>>>>>>>>>>>>>> --
>>>>>>>>>>>>>> -Todd
>>>>>>>>>>>>>>
>>>>>>>>>>>>>
>>>>>>>>>>>>>
>>>>>>>>>>>>>
>>>>>>>>>>>>> --
>>>>>>>>>>>>> -Todd
>>>>>>>>>>>>>
>>>>>>>>>>>>
>>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>> --
>>>>>>>>>>> -Todd
>>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>> --
>>>>>>>>>> -Todd
>>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>> --
>>>>>>>>> -Todd
>>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> --
>>>>>>> -Todd
>>>>>>>
>>>>>>
>>>>>>
>>>>>
>>>>>
>>>>> --
>>>>> -Todd
>>>>>
>>>>
>>>>
>>>
>>>
>>> --
>>> -Todd
>>>
>>
>>
>


-- 
-Todd
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