Asynchronous writes (Servlet and WebSocket)

[Steffen Heil (Mailinglisten)]

Hi


I am investigating, how I can archive asynchronous writes with tomcat.

For servlets I came up with code like this:
        final AsyncContext context = request.startAsync();
        final ServletInputStream input = request.getInputStream();
        final ServletOutputStream output = response.getOutputStream();
        ChannelProcessor processor = new ChannelProcessor( channel, input, 
output );
        context.addListener( processor );
        input.setReadListener( processor );
        output.setWriteListener( processor );

While ChannelProcessor is my class that implements (beside others) 
WriteListener, so I get notified, when the ServletOutputStream is ready to send 
more data.
However, looking at the code, I suspect that "output.write( byte[] buffer )" 
will still block, if the amount of data in buffer is larger than the maximum 
size of the OutputBuffer used by that connection:

Call stack:
  CoyoteOutputStream.write   (is ServletOutputStream.write)
  OutputBuffer.write
  ByteChunk.append
  ByteChunk.flushBuffer
  OutputBuffer.realWriteBytes
... from here on I am not sure.


For WebSockets there is
        session.getAsyncRemote().sendBinary( buffer, handkler );

But that calls ServletOutputStream.write (maybe from another thread)


So, are these really asynchronous?
Is a call to ServletOutputStream.write always guaranteed to return without 
blocking?`
Where is that implemented?


Regards,
  Steffen

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