Restrictions for lock coarsening?

[Christian Thalinger]

On Thu, 2009-01-08 at 10:11 -0800, Tom Rodriguez wrote:
> It was definitely done as a result of benchmarking and there were  
> definitely regressions.  I don't have any information about which  
> benchmarks showed problems though.  I think it was done early enough  
> that other changes and improvements to biased locking might have  
> helped.  Maybe that's just wishful thinking on my part.

I try to have a look at it.  Does setting BiasedLockingStartupDelay=0
use biased locking for all locks?  I'm not sure:

$ gamma -XX:+TraceBiasedLocking -XX:BiasedLockingStartupDelay=0 x
VM option '+TraceBiasedLocking'
VM option 'BiasedLockingStartupDelay=0'
Aligned thread 0x0000000000446418 to 0x0000000000446800
Aligned thread 0x0000000000453fc8 to 0x0000000000454000
Aligned thread 0x0000000000455d18 to 0x0000000000456000
Aligned thread 0x0000000000597968 to 0x0000000000598000
Aligned thread 0x000000000059d448 to 0x000000000059d800
Aligned thread 0x000000000059f658 to 0x000000000059f800
Aligned thread 0x00000000005d5688 to 0x00000000005d5800
Aligned thread 0x00000000005d7f08 to 0x00000000005d8000
Aligned thread 0x00000000005db198 to 0x00000000005db800
Aligned thread 0x00000000005df558 to 0x00000000005df800
Biased locking enabled
Aligned thread 0x00000000005eb5a8 to 0x00000000005eb800
Exception in thread "main" java.lang.NoClassDefFoundError: x
Caused by: java.lang.ClassNotFoundException: x
	at java.net.URLClassLoader$1.run(URLClassLoader.java:217)
	at java.security.AccessController.doPrivileged(Native Method)
	at java.net.URLClassLoader.findClass(URLClassLoader.java:205)
	at java.lang.ClassLoader.loadClass(ClassLoader.java:323)
	at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:294)
	at java.lang.ClassLoader.loadClass(ClassLoader.java:268)
	at java.lang.ClassLoader.loadClassInternal(ClassLoader.java:336)

- Christian