On Sat, May 9, 2015 at 10:09 PM, Ben Coman <btc@openinworld.com> wrote:

From my limited experience bug hunting, calling #changed: from a thread other than the UI thread is a source of evil.  There are too many assumptions throughout the system that the UI is single threaded.  Can anyone advise me that is not a proper belief?

Then that implies that a Transcript implementation where #nextPut: direct calls #changed:

is not appropriate for use with multi-threaded applications.  In Pharo, #changed: is only called from #stepGlobal, which is called from doOneCycle:.  (This came about as a last minute bug fix before Pharo 3 release and maybe could use some cleanup.

Separating the UI from Transcript into its own viewer might be a good idea, but actually it would not solve Stef's case since his code would still be running in the UI thread -- unless the viewer ran in another thread, which would have its own complexities.

I think the point about efficiency is significant. The following example...

     Time millisecondsToRun: [ 1000 timesRepeat:  [ Transcript show: 'x' ] ]

on Squeak 4.5 --> 12749ms

on Pharo 50029 --> 2ms

As a point of comparison, on VW 8.0 --> 43817ms 

and so you might guess, VW 8.0 outputs each 'x' immediately.

cheers -ben