using the sendfile system call on Darwin

[Greg Lewis]

On Tue, Jan 26, 2010 at 01:33:06AM -0800, Michael Allman wrote:
> I would like to update jdk/src/solaris/native/sun/nio/ch/FileChannelImpl.c 
> so that the Java_sun_nio_ch_FileChannelImpl_transferTo0 function calls the 
> sendfile system call on Darwin.  I have a few questions:
> 
> 1.  Is there a cpp #define for Darwin?  If not, how do I tell cpp whether 
> the system is Darwin or not?

The rest of the code uses

#ifdef __APPLE__

> 2.  Are there tests that exercise 
> Java_sun_nio_ch_FileChannelImpl_transferTo0 or the java method 
> FileChannel.transferTo?

Some of the tests in jdk/test/java/nio/channels/FileChannel/ may be useful,
I haven't looked them over though.

> 3.  Why doesn't the existing BSD code just return IOS_UNSUPPORTED?  For 
> instance, look at lines 223 and 224.  If there's no sendfile function on 
> Solaris, the function just returns IOS_UNSUPPORTED.  The caller handles 
> that return value gracefully.  The existing BSD code looks needlessly 
> complex to me.

All of the BSDs have sendfile, its just limited to only sending the file to
a stream socket rather than any file descriptor, which Solaris and Linux
allow.  It's fairly easy to implement code that will do that though, so
that's what was done rather than throwing errors when a non-socket file
descriptor was used.

Note that MacOS X seems to have the same limitations as all the other BSDs
in terms of what type of file descriptor can be used as the destination:

http://developer.apple.com/Mac/library/documentation/Darwin/Reference/ManPages/man2/sendfile.2.html

If NIO in general interests you, then a project we really need someone to
work on is porting NIO2 to BSD.  None of the BSDs have the epoll mechanism
used on Linux or whatever Solaris uses (which I can't recall off the top of
my head right now).  The suggestion is to use kqueue(2) on BSD.

-- 
Greg Lewis                          Email   : glewis at eyesbeyond.com
Eyes Beyond                         Web     : http://www.eyesbeyond.com
Information Technology              FreeBSD : glewis at FreeBSD.org