Re: What happened to Double Buffering?

In article <520u5497nbencs0oagpr8chc4sbial8ast@[EMAIL PROTECTED]
>,
 Roedy Green <see_website@[EMAIL PROTECTED]
> wrote:
> Today, when we have RAM coming out our ears we have reverted back to
> SINGLE buffering.  We alternate between processing and waiting for I/O
> on the same buffer.
> 
> What is the matter with us? It is as though we imagine we still have a
> single threaded DOS OS.

Nothing is the matter with us.  CPUs got faster.  That's what it sounds 
like you are seeing.

Let's say there are two buffers, so while the application is processing 
one, the I/O system is filling the other.  Your timeline would then be 
something like this:

   I/O System                    Application
   ----------                    -----------
                                 Request data, wait for response
   start filling buffer #1       ...
   ...                           ...
   ...                           ...
   ...                           ...
   ...                           ...
   ...                           ...
   ...                           ...
   ...                           ...
   finish filling buffer #1      ...
   give buffer #1 to app         ...
   start filling buffer #2       start processing buffer #1
   ...                           finish processing buffer #1
   ...                           update progress bar
   ...                           request data, wait for response
   ...                           ...
   ...                           ...
   ...                           ...
   ...                           ...
   finish filling buffer #2      ...
   give buffer #2 to app         ...
   start filling buffer #1       start processing buffer #2
   ...                           finish processing buffer #2
   ...                           update progress bar
   ...                           request data, wait for response
   ...                           ...
   ...                           ...
   ...                           ...
   ...                           ...
   finish filling buffer #1      ...
   give buffer #1 to app         ...
   start filling buffer #2       start processing buffer #1
   
The app pauses because the app can consume data much faster than the 
disk can provide it.

-- 
--Tim Smith