Re: Streams and Concurrency

[stt@houdini.camb.inmet.com (Tucker Taft)]

It seems clear that the stream attributes do not directly support the 
logging from multiple tasks, with interleaving occurring only
between "top-level" objects, as desired by this application.
Furthermore, they don't support reading without waiting.

However, it should be simple enough to build a generic package
which provides the desired functionality.

Each current "top-level" use of a stream attribute in the application
would be changed to be a call on a "read/write" or "input/output" routine of an 
appropriate instance of this generic package.  Such a routine would 
acquire a lock on the stream, invoke the corresponding stream attribute,
and release the lock.  

Furthermore, to support non-blocking read, you would need to add some 
kind of marker into the stream itself, I suspect, to be placed between 
"top-level" objects in the stream.  Then, when you call the non-blocking
"read" or "input" routine of the instance of this generic package,
it would call a routine of the underlying stream which would indicate
whether there is an "entire" top-level object already buffered up.
If not, the non-blocking read/input routine of the generic would
return a "not available" indicator.  If there is an entire top-level
object buffered up, the read/input routine would use the corresponding
stream attribute to read the data from the stream, confident that it
wouldn't block or get an end-of-file indication during the read.

--
-Tucker Taft   stt@averstar.com   http://www.averstar.com/~stt/
Technical Director, Distributed IT Solutions  (www.averstar.com/tools)
AverStar (formerly Intermetrics, Inc.)   Burlington, MA  USA