close() of active socket does not work on FreeBSD 6

[Daniel Eischen]

[CC trimmed]

On Wed, 13 Dec 2006, David Xu wrote:

> On Wednesday 13 December 2006 04:49, Daniel Eischen wrote:
>>
>> Well, if threads waiting on IO are interruptable by signals,
>> can't we make a new signal that's only used by the kernel
>> and send it to all threads waiting on IO for that descriptor?
>> When it gets out to actually setup the signal handler, it
>> just resumes like it is returning from an SA_RESTART signal
>> handler (which according to another posting would reissue
>> the IO command and get EBADF).
>
> Even if you have implemented the close() with the interruption, another
> thread openning a file still can reuse the file handle immediately,
> according to specifications, the lowest free file handle will be returned,
> if SA_RESTART is used, the interrupted thread restart the syscall,
> it will be using a wrong file, I think even if we have implemented the
> feature in kernel, useland threads still has serious race to fix.

If you use a special signal that is only used for this
purpose, there is no reason you have to try the IO operation
again.  You can just return EBADF.

Anyway, this was just a thought/idea.  I don't mean to
argue against any of the other reasons why this isn't
a good idea.

-- 
DE