<AWT Dev> Historical use of Thread.sleep(0) in the GUI?

[David Holmes]

Hi Folks,

I'm currently looking at some hotspot cleanup surrounding the 
ConvertSleepToYield VM flag. When this flag is true it replaces a call 
to Thread.sleep(0) with a platform yield call; otherwise the platform 
"sleep" function is called with sleep time of 1ms. (Note: no reasonable 
Java code should ever use Thread.sleep(0) :) )

This flag stems back to "pre-historic" days when hotspot was replacing 
the classic VM on Windows, and IIUC only a Solaris sparc implementation 
existed. The default for Windows (and all platforms subsequently ported 
to - including Solaris x86!) was to set the flag true; while for Solaris 
sparc it was set to false. The comment in the code is:

// When ConvertSleepToYield is on, this matches the classic VM 
implementation of
// JVM_Sleep. Critical for similar threading behaviour (Win32)
// It appears that in certain GUI contexts, it may be beneficial to do a 
short sleep
// for SOLARIS

Does anyone have any knowledge of what those GUI contexts may have been? 
(I suspect some old motif based environment.)

As I said, for Solaris x86 the flag value differs from sparc (presumably 
an oversight) for what should be an OS issue I would think. Can anyone 
think of a reason why the GUI on sparc may respond differently to x86 in 
the context of using a sleep(0)?

Finally, as I want to get rid of the flags altogether I first need to 
change the setting on sparc. Are there any specific GUI responsiveness 
tests that I might run to ensure this change has no averse impact?

Thanks,
David