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From "Alan D. Cabrera" <>
Subject Re: TriFork CORBA donation
Date Sun, 16 Oct 2005 00:27:11 GMT
How are things going?  Do you think that it's possible to get the code 
in our repo and you work from there?


Kresten Krab Thorup wrote, On 9/16/2005 9:04 AM:

> Hi there, ...
> It has been up to a slow start, but I have finally gotten something  
> rolling now.
> As I have mentioned earlier, I wanted to redo the I/O subsystem, and  
> this is going quite well.  The first milestone I am targeting is to  
> be able to do client side stream-based invocations; i.e. be able to  
> do invocations using a generated stub.  This is a sufficiently small  
> thing that it is doable relatively quick (sigh), and also gets around  
> to do most of the hairy parts of I/O.
> This part I am writing from scratch, since the new I/O transcends  
> most of this code.  This part is quite close to completion, and if  
> someone wants to see the code I'd be happy to share it.  Here, I have  
> some notes on the I/O system; ...
> The I/O system is designed with the following properties:
> - it eliminates copying (double buffering)
> - i/o can be off-loaded to a separate selector thread
> - nio/select is used to avoid having an active thread listening for  
> incoming messages
> - transport buffers are allocated only once, and have fixed size.
> - facilitate multiplexing requests and bidirectional invocations.
> In this terminology, a transport (which may be a socket or an in- 
> memory pipe, for instance) has the following API:
> interface Transport {
>    InputChannel getInputChannel();
>    OutputChannel getOutputChannel();
>    void setInputHandler(InputHandler handler);
>    void close();
>    void start();
>    void signalCondition(Object conditionKey, Object user_data);
>    Object waitForCondition(Object conditionKey);
> }
> Only one thread can have the input channel at one time, and only one  
> thread can have the output channel.  Calls to getInputChannel(), and  
> getOutputChannel() will block until the channel is available.  If  
> someone else has "taken" the channel, then the requestor will block  
> until the other party relinquishes it.  This semantics is used to  
> handle multiplexing multiple client threads using the same transport  
> to do invocation, and similarily on the server side to  handle  
> multiple threads sending responses.
> interface Channel {
>    void close();
>    void relinquish();
> }
> Closing a channel semantically puts an end-of-stream marker into the  
> channel's data.  For an OutputChannel, once the EOS reaches the  
> underlying transport layer (i.e. the data ahead of it has been  
> written), it is effectuated as a half-close.  For an InputChannel,  
> the half-close is effectuated right away, and the client of the input  
> stream will read and end-of-file when there is no more buffered data  
> available.
> When input becomes available in the underlying transport, and there  
> is no current thread that owns the input channel, then control is  
> passed to the input handler in a new thread taken from some worker pool.
> The transport also has a built-in signaling mechanism, that allows  
> the InputHandler to parse a message header (including e.g. a  
> request_id) and then pass control to someone waiting for a given  
> reply.  Such waiters can also participate in the processing of  
> available input.
> An output channel allows you to put data into the transport, and  
> provides a mechanism to set markers.  Markers are used to handle  
> fragmentation and other things where a size needs to be written into  
> some place in the stream.
> interface OutputChannel extends Channel {
>     putByte(byte value);
>     put(byte[] data, int off, int len);
>     // ... other put methods ...
>    void flush();
>    OutputChannelMark setMark(OutputChannelMarkHandler handler);
> }
> Now, if the output channel's buffer runs full, then the mark handler  
> is called, so that the
> interface OutputChannelMarkHandler {
>    void willFlush(OutputChannelMark mark);
> }
> OutputChannelMark provides a ByteBuffer-like view of the stream,  
> where index 0 is the position of the marker.  You cannot put data  
> beyond the mark's limit, which is equal to the amount of bytes  
> written to the channel since the mark.
> interface OutputChannelMark {
>     void putByte(int idx, byte value);
>     void putInt(int idx, int value);
>     int limit();
>     void release();
>     OutputChannel getOutputChannel();
> }
> Calling release() on an OutputChannelMark will release underlying  
> buffer space up to this mark (unless of cause there is a non-released  
> marker that was set earlier in the stream).
> The OutputChannelMark can also give you the channel that i came from,  
> and so inside the handler you can do stuff like this to handle GIOP  
> fragmentation dynamically based on when the underlying buffer runs full.
>    class FragmentHandler implements OutputChannelMarkHandler {
>        void willFlush( OutputChannelMark mark) {
>             int message_size = mark.limit();
>             if (!logical_stream_has_ended) {
>                 mark.putByte(7, 2); // write "hasMoreFragments" bit
>             }
>             mark.putInt (8, message_size);  // write message size  
> into GIOP header
>             mark.release();
>            if (!logical_stream_has_ended) {
>                 mark.getOutputChannel().setMark(this);
>                 write_fragment_header();
>             }
>        }
>    }
> I use the markers to implement GIOP fragments, and also to do  
> chunking for values.  The mechanism cannot really be used for  
> encapsulations because they can span GIOP messages.
> So, ... on top of this abstraction layer I have implemented a fair  
> chunk of the GIOP/CDR encoding stuff up to the point where a client  
> can perform a request, but it doesn't work yet...
> My thinking is that once this has reached a point where I can  
> actually do a hello world invocation on a foreign ORB, then it would  
> be a good point to bring in some more people.
> Once we're past this, I have some larger chunks of the original  
> Trifork ORB that we can bring to play.  You're welcome to have a look  
> at the code though, and chip in with your comments.
> Kresten Krab Thorup
> "We do not inherit the Earth from our parents, we borrow it from our  
> children." Saint Exupery
> On Sep 15, 2005, at 10:46 PM, Alan D. Cabrera wrote:
>> How are things going on this?
>> I hope that what will be donated will not be "gold plated" so that  
>> the community can participate in its integration into Geronimo.  I  
>> know that a few people, including people from OpenORB, are  
>> interested in helping out.
>> Regards,
>> Alan

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