Microsoft Windows has one thing in common with Smalltalk: It works by sending messages. A Windows message can also be “posted,” i.e., it is put at the end of the Windows message queue, and the sender doesn’t wait for a synchronous response. The idle queue in Cincom® ObjectStudio® classic was designed in part to mirror this activity in Windows. While the design as a whole is very useful and sometimes plain necessary, it can be overused.

In ObjectStudio classic, it was pretty standard to delay some action using System>>whenIdleSend:to:args:. The VM made sure that the message was executed after the current code was executed, but before ObjectStudio became “idle” It was also assumed that those messages were to be executed in the same order in which they were added to the queue. Since most applications never used multiple, native threads, the assumption was correct. Unfortunately with ObjectStudio 8 and the so called “Multi-Proc-UI,” these assumptions are not 100% correct any more.