Messages in this thread |  | | From | "J. Dow" <> | Subject | Re: thread rant [semi-OT] | Date | Sat, 2 Sep 2000 00:24:07 -0700 |
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> 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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