[fpc-pascal] fpselect does not work on linux

[Jonas Maebe]

On 09 May 2009, at 09:38, Rainer Stratmann wrote:

> To find out if a nonblocking socket has connected I use the  
> following piece of
> code:
>
> With windows that works, but with linux I get alwas the result that  
> the socket
> is writable.
>
> function is_writable_socket( sck : integer ) : boolean;
> var
>  fds : tfdset;
>  tv  : timeval;
> begin
>  {$ifdef linux}   fpfd_zero( fds ); fpfd_set( sck , fds ); {$endif}
>  {$ifdef windows}   fd_zero( fds );   fd_set( sck , fds ); {$endif}
>  tv.tv_sec  := 0;
>  tv.tv_usec := 0;
>  //                 socket+1 , read , write , except , timeout
>  {$ifdef linux}
>  result := fpselect( sck + 1 ,

Where does the "+ 1" come from?

> nil  , @fds  , nil    , @tv ) > 0;

This is probably unrelated to your problem, but you have a bug here.  
(fp)select can also return EINTR (possibly under Windows as well, I  
don't know), in which case you have to retry. You need something like  
this:

repeat
   res:=fpselect( sck + 1 , nil  , @fds  , nil    , @tv );
until (res<>-1) or (fpgeterrno<>ESysEIntr);

Note that you have to use this construct for many low level unix  
calls. Check the man pages to see which routines can return EINTR and  
may need restarting.


Jonas