My original intention of having a snapshot was not so much as to have a quick restart but to be able to migrate apps a la distributed JVM efforts (http://djvm.anu.edu.au/) as Steve has mentioned in this thread earlier.
As you say I guess persistence along with machine specific JIT code might be a hard problem to solve. Sun's efforts in this direction is a good partial solution. But taking care of the environmental parameters like open JDBC connections etc would also have to be implemented if any movement in this direction is to be expected. Regards ~sundar -----Original Message----- From: Nick Lothian [mailto:[EMAIL PROTECTED] Sent: Tuesday, May 17, 2005 10:36 AM To: harmony-dev@incubator.apache.org Subject: RE: Introduction, and a question > > 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 IMPORTANT: This e-mail, including any attachments, may contain private or confidential information. If you think you may not be the intended recipient, or if you have received this e-mail in error, please contact the sender immediately and delete all copies of this e-mail. If you are not the intended recipient, you must not reproduce any part of this e-mail or disclose its contents to any other party. This email represents the views of the individual sender, which do not necessarily reflect those of education.au limited except where the sender expressly states otherwise. It is your responsibility to scan this email and any files transmitted with it for viruses or any other defects. education.au limited will not be liable for any loss, damage or consequence caused directly or indirectly by this email.
