Re: [Jikesrvm-core] Re: gnu.java.nio.channels.FileChannelImpl

[Steven Augart]

Michael Koch wrote:
> Which leads us to the discussion again what type a file descriptor 
> should have. Is an int (4 byte) enought for 64 bit archs ? What about 
> 128 bit archs in the future ? From the last discussions fd should be at 
> least long when. I know that GNU classpath currently uses int but when 
> we change it we can try to do it right.

Yes, an int is plenty of space.  It will always be plenty of space
unless you plan to be opening more than 2^31 files (and that exceeds
the limits of every Unix-like system that i know of).

I should caution here that I don't have a copy of the POSIX spec.
However, the manual page for open(2) on Linux says:

       The  open() system call is used to convert a pathname into
       a file descriptor (a small, non-negative integer  for  use
       in  subsequent  I/O  as with read, write, etc.).  When the
       call is successful, the file descriptor returned  will  be
       the lowest file descriptor not currently open for the pro-
-------^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^­
       cess.

This guarantee is part of historical Unix semantics
for open() -- there is still code around that (for example) closes
file descriptor 0 (standard input) and then opens some other file,
expecting that any successful open will assign descriptor 0 to
the opened file.

So, if open() ever stopped handing out the lowest descriptor
it could, existing Unix code would break.

--
Steven Augart

Jikes RVM, a free, open source, Virtual Machine:
http://oss.software.ibm.com/jikesrvm