masinter
commented
4 years ago John Cowan wrote
From the Smalltalk: Bits of History, Words of Advice book, in the chapter "The Design and Implementation of VAX/Smalltalk-80" by Stoney Ballard (Three Rivers) and Stephen Shirron (DEC), pp. 146-47:
The Smalltalk-80 system as distributed is not designed to either run background processes or co-exist on a timesharing system. This is due to the large number of places where the code loops waiting for a mouse button. The system can be converted to one which is entirely event driven by inserting wait messages to an "any event" semaphore into the loops. We found these loops by noticing whenever the idle process was not running, yet nothing else seemed to be happening. We would then type control-C to interrupt the Smalltalk-80 system and find out who was responsible. The debugger was then used to edit and recompile the offending methods. Converting all the interaction to an event-driven style allowed background Smalltalk-80 processes to run whenever the user was not actively interacting with the Smalltalk-80 system.
It is generally considered uncivil to run programs that are not doing anything worthwhile on a timesharing system. To fix this, we replaced the Smalltalk-80 idle process with one that called two special primitives. The Smalltalk-80 code for this is as follows. IdleLoop [true] whileTrue: [[Smalltalk collectGarbage] whileTrue. Smalltalk hibernate]
The collectGarbage primitive performed an incremental activation of the garbage collector, returning false if there was nothing left to do. The hibernate primitive suspended the Smalltalk-80 VMS process, letting other users run. The hibernate primitive returned whenever an external event happened. Since this loop runs at the lowest priority, it is preempted by any Smalltalk-80 process with something to do.
This made us more popular with the other users of the VAX, and also reduced the overhead of the garbage collector when interacting with the Smalltalk-80 system in a bursty manner (which is usually the case). The Smalltalk-80 process itself also benefited from this because the VMS scheduler assigns a lower priority to compute-bound processes. By hibernating often enough, the Smalltalk-80 process would preempt other users running compilers and the like, leading to a snappier response when browsing or editing.
blakemcbride
Kirtai
moon-chilled
yasuhiko-kiuchi
Anzus
nbriggs
waywardmonkeys
sethm
As many have noted (including most recently @pmcjones )
there isn't a straightforward solution because Lisp always is running, if only to track the mouse and blink the cursor, handle incoming network packets, and do other periodic polling events many times a second. But it might be possible to reduce the load if all the processes are hung in I/O or timer wait.