The Single Input Queue- by Anders Thue Pedersen

What is the Single Input Queue (SIQ), and how does FixPak 17 fix it?

Now that IBM has released its SIQ fix, here is a technical description of what the SIQ is, what was the problem, and how IBM has fixed it.

Due to the architecture of OS/2 all processes (programs) uses the same message queue to get messages from the system. This means that whenever you resize, move, etc. a Presentation Manager (PM) program it gets a lot of messages which tell the program to redraw the screen. If a program (like the infamous VIEW.EXE) does't handle the messages, the message queue will be filled in a few tenths of a second and the PM hangs.

This doesn't mean that OS/2 hangs; usually you'll only have to wait a few minutes and the program starts to remove messages from the queue and the PM will work normally again. The other way to get around this problem is to press Ctrl-Esc, and the "This program is not responding to system requests" dialog will appear. Here you can close the program or cancel the dialog but it isn't always the offending program that is closed, and often it doesn't help at all.

But all this is history now...

After installing FixPak 17 you'll have to put the following line in your CONFIG.SYS:


This tells the PM that it should enable the SIQ-Fix.

How does the queue work now? First of all the PM hasn't got multiple queues, so programs are still able to fill the message queue, but now it is possible to get the system to remove messages that a program doesn't.

Sadly, the PM doesn't do this for you, you'll still have to press CTRL-ESC to get the "This program is not responding to system requests" dialog, but now if you select "cancel" the program that isn't responding to the system will be disabled until it begins removing its messages from the queue. Of course, if you chose "close" the program will be closed.

Best of all, the dialog and the close function is much, much faster than it was previously. Compared to NT, this is OS/2's only weakness (because NT has multiple queues). With the SIQ fix OS/2 takes one step closer to complete superiority. Thanks IBM!

Anders Thue Pedersen is a 24 year old student at Denmark's Technical University, working at IBM in the Dealer Support Center. He's been using OS/2 for 2 years.

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