[libdispatch-dev] Mountain Lion libdispatch for Linux

[Nick Hutchinson]

Hi Daniel,

Thanks for your repsonse. I've been poking around, and I think the dispatch_io test failures might point to a bug in libdispatch proper.

I don't understand most of the logic in io.c, but it seems that in certain cases, a Dispatch I/O channel's cleanup handler can execute concurrently with an I/O handler, instead of waiting until all I/O handler blocks have returned.

I was experiencing this because there were a number of zero-length files in my /usr/lib folder, so the unit test was calling dispatch_io_read() with a `size` parameter of zero. Looking at the io.c code, I see that a request for a read or write of length zero is special-cased in _dispatch_operation_create(), and the I/O handler is enqueued immediately.

Maybe this is the source of the failures? If I update the dispatch_io.c test to call dispatch_io_read() with SIZE_MAX for the `size` parameter, the failures go away.

Regards,
Nick

On 17/10/2012, at 8:03 PM, Daniel A. Steffen wrote:

> Hi Nick,
> 
> awesome, thanks for the patches!
> 
> looking at the test failures:
> 
> the dispatch_vnode failure means not all vnode notifications were seen that should have been generated in response to the file rename()s perfomed, this is likely fixable by adjusting the dispatch_semaphore_wait timeout in the test, but could also indicate a problem in the kevent library or somewhere below
> 
> dispatch_starfish is essentially a stress test for multithreaded malloc, looks like the latency allowed by the test was exceeded in one case, this does not indicate a serious problem (the timing constants in the test would need to be adjusted for Linux for this to pass).
> 
> the dispatch_io failures look more serious and likely indicate a problem with the port of io.c, the asynchronous IO does not seem to be performed correctly, but I can't tell anything more specific about the cause from the output, so you'll probably need to do some debugging...
> 
> Daniel
> 
> 
> On Oct 16, 2012, at 22:56, Nick Hutchinson <nshutchinson at gmail.com> wrote:
> 
>> Hi all,
>> 
>> I've written some portability fixes to get Mountain Lion's libdispatch up and running on Linux, and my fork is up on Github for anyone who's interested: https://github.com/nickhutchinson/libdispatch. 
>> 
>> I used Mark Heily's patches[1] that were previously posted on this list as a starting point. Note that I've had no previous experience with Autotools, and so the patches might be a little rough around the edges. Feedback is welcome.
>> 
>> The test suite builds, and most tests pass. However, the following three tests are failing, and I'd love to know why!
>> - dispatch_starfish
>> - dispatch_io
>> - dispatch_vnode
>> 
>> The test output is here: https://gist.github.com/3903724
>> 
>> Cheers,
>> Nick
>> 
>> [1] http://lists.macosforge.org/pipermail/libdispatch-dev/2012-August/000676.html
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