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

[Matthias Urlichs]

At 22:35 +0100 2001-06-06, Alan Cox wrote:
>  > This report describes a problem in the usage of file descriptors across
>>  multiple threads. When one thread closes a file descriptor, another
>>  thread which waits for an I/O on that file descriptor is not notified
>>  and blocks forever.
>
>THe I/O does not block forever, it blocks until completed.

That's still "forever" if you don't specify a timeout in the select.

>The actual final
>closure of the object occurs when the last operation on it exits

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.

A related problem is that the second thread my be inside a blocking 
read() instead of a select() call. It'd never continue.  :-(

HOWEVER: IMHO it's bad design to distribute the responsibility for 
file descriptors between threads.
Therefore I think that this behavior is a bug, but it's not one that 
needs to be fixed yesterday.
-- 
Matthias Urlichs