Re: sockets /network programming Requirements

From: williamkempf_at_[hidden]
Date: 2001-07-30 15:22:35

--- In boost_at_y..., "Greg Colvin" <greg_at_c...> wrote:
> From: <williamkempf_at_h...>
> > ...
> > * The "must be portable" requirement may prove more than vexing. 
Unix
> > programmers rely heavily on select(), while Windows programmers 
can
> > only make very limited use of this and rely almost completely on
> > asynchronous routines not available to Unix programmers.  The
> > simplest way to insure portability is to support only blocking i/o
> > with very limited ability to check for available data, but this 
can
> > severely complicate coding.  A possibly better solution is to 
provide
> > a callback mechanism similar to the asynchronous routines in Win32
> > that do not rely on Win32 specific WndProc mechanisms.  (I never
> > understood why I/O was tied to a GUI object in Win32 asynchronous
> > routines.) Such an interface could be coded portably using 
threads on
> > any platform, though the design will be much more complicated.
> > ...
> 
> It is possible to paper over these Unix/Windows differences, since 
most
> all the available java sockets implemenations do so.
> 
> In our implementation of the java socket classes we use poll() 
rather
> than select() on Unix, and WaitForMultipleObjects() on Windows.  We
> don't wait for a Windows GUI object, but instead for the hEvent 
that we associate with the socket with WSAEventSelect().  The code
> belongs to
> Oracle, so I can't post it, but there are other more open java
> implementations one could study.

I guess I wasn't overly specific.  This is the "very limited ability 
to check for data" I mentioned.  In fact, this can be done with select
() on Win32 to keep the implementation more uniform across 
platforms.  The drawbacks are that this select() mechanism is valid 
only for sockets.  Unix users mix socket, file, pipe and keyboard 
descriptors in a single call to select() to wait for multiple I/O 
events, but the Win32 select (and the WSAEventSelect) will only work 
for socket descriptors.

Bill Kempf