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

[Alexander Viro]

On Thu, 7 Jun 2001, Matthias Urlichs wrote:

> > > 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.

Then what EBADF are you talking about?
 
> 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..?

FreeBSD, Plan 9: same as Linux (get file by descriptor, forget about
descriptor you've used for that)
OpenBSD, NetBSD: good chance of kernel panic (the whole handling of shared
descriptor tables is broken)

the rest: entirely different threads model.

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

So why would closing a descriptor have any effect on them? struct file
is alive and well, held by the operation we are doing.