This sounds like how java works under OS X.
Newbie question: What is to stop us from caching JITed code? .NET/ mono does this as far as I know?
Stuart On 17 May 2005, at 06:05, Nick Lothian wrote:
El lun, 16-05-2005 a las 16:08 +0530, Subramanian, Sundar escribió: (...)
I guess what Brad is asking is for a snapshot of the state of JVM. This would be really useful to migrate stuff from one environment to another preserving the underlying state.
I have mixed feelings about having a "save image" __a la__ Smalltalk, if this is what you are meaning. While delivering an image looks tempting, state gets corrupt in unpredictable ways, and having ways to track changes becomes a nightmare.
The Smalltalk community has worked hard in this (hard) problem, but I'm still not sure if it would make sense in the java world. Java is a system-oriented language, and the ability to save the whole VM state and recover from this saved image would bring additional constraints to the Virtual Machine implementation. For instance, machine specific JIT code should be invalidated upon save, negating a substantial part of the advantages of a saved image (faster startup).
This said, if VM implementors out there find easy ways to meet these constraints w/o burdening runtime or memory requirements, it could be an area for experimenting.
This looks like it would be related to the stuff Sun has done with class data sharing in the 1.5 JVMs:
"When the JRE is installed on 32-bit platforms using the Sun provided installer, the installer loads a set of classes from the system jar file into a private internal representation, and dumps that representation to a file, called a "shared archive". Class data sharing is not supported in Microsoft Windows 95/98/ME. If the Sun JRE installer is not being used, this can be done manually, as explained below. During subsequent JVM invocations, the shared archive is memory-mapped in, saving the cost of loading those classes and allowing much of the JVM's metadata for these classes to be shared among multiple JVM processes." [1]
This isn't quite the same as saving JIT'ed code, but it sounds like it is saving the pre-parsed and verified class files.
Nick
[1] http://java.sun.com/j2se/1.5.0/docs/guide/vm/class-data- sharing.html
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