> In summary, when "multithreading" floats into your mind, think
> "concurrency." Think very carefully about how you might simultaneously
> exploit all of the independent resources in your computer. Due to the long
> and complex history of OS development, a different API is usually required
> to communicate with each device. (e.g. old-school UNIX has always handled
> non-blocking network I/O with select(), but non-blocking disk I/O is
rather
> new and must be done with AIO or threads; and don't even ask about
> asynchronous access to the graphics card =).
Dan, another thing to consider with multithreading is that it is a way to
avoid "convoy" effects if there is a nice priority mechanism for first in
first out messaging. Until NT crufted in its IO Completion model it was
highly prone to either starvation or convoy problems with certain problems.
If you fired off reads on several interfaces which all experienced about the
same problem the first on in the array searched by the multiple object
wait function was more likely to get serviced than the others. The initial
solution reordered the list each pass through the wait. IO Completion
actually added in first in first out messaging for all the messages
reaching that particular wait for io completion call. This made a VERY
measureable improvement in performance overall. You can run into
the same problems with psuedo-threading in state machines with
polling loops only it's a whole lot uglier. (Been there, done that, kicked
myself, bought the teeshirt in disgrace, and retreated to a proper
solution.)
(Heh, incidentally I was rather surprised by the time I hit NT tasking
to discover its array based message handling. I was used to the
FIFO message queueing on AmigaDOS that it enjoyed from day
zero. So I wrote as if I had that on NT.... I learned the hard way.)
{^_^}
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