Re: PROBLEM: I/O system call never returns if file desc is closed in the

["Matthias Urlichs" <smurf@noris.de>]

Hi,

Alexander Viro:
> > Select is defined as to return, with the appropriate bit set, if/when 
> > a nonblocking read/write on the file descriptor won't block. You'd 
> > get EBADF in this case, therefore causing the select to return would 
> > be a Good Thing.
> 
> Bzzert. Wrong. It may easily block. open() from another thread might
> grab that descriptor just fine.
> 
Sorry, s/file descriptor/file-or-socket-or-whatever.

Actually trying to read from this descriptor is of course a Bad Thing, but
that just means that the programmer forgot to record the file closing in
the program's global state.

> > A related problem is that the second thread my be inside a blocking 
> > read() instead of a select() call. It'd never continue.  :-(
> 
> Yes. So close() doesn't abort read(). Why would it?
> 
Well, if it triggers a return from select(), which it currently doesn't
do under Linux, then it should also trigger a return from read() (with
either zero or -EBADF).

I wonder whether any other Unixes do that..?

> Operations like read, select, etc. act of files. Not on descriptors.
> 
Right -- I sort-of implied that. My fault.

-- 
Matthias Urlichs     |     noris network AG     |     http://smurf.noris.de/