Summary

We create aliases for existing CDS command-line flags under the "AOT" umbrella to make them more intuitive to users of upcoming AOT optimizations.

Problem

Many of planned AOT (ahead-of-time) optimization in Project Leyden are based on the existing CDS technology in HotSpot. However, many command-line flags related to CDS, as well as the name CDS itself (which ostensibly stands for Class Data Sharing) look out of place. It's better to have alternative names for these options that are grouped under "AOT", so that they will be consistent with future command-line options that will be introduced by Project Leyden.

Solution

Add new command options that are mapped to existing options:

• -XX:AOTCache=<file>.aot
• -XX:AOTMode=off/auto/on/record/create
• -XX:AOTConfiguration=<file>.aotconfig

Specification

[1] The three options listed above are all of the type ccstr, which means they can be assigned in the command-line to a text string.

[2] AOTMode can have the values of off, auto, on, record, or create. The other two options can be assigned to arbitrary file names (provided the current user has read and/or write access to these files). It's recommended (but not required) to use .aot and .aotconfig as file extensions for AOTCache and AOTConfiguration, respectively.

[3] If AOTMode is not assigned, it has the default value of auto.

[4] When -XX:AOTCache=<file>.aot is specified, and AOTMode is auto, the JVM behaves as if "-Xshare:auto -XX:SharedArchiveFile=<file>.aot" are specified. I.e., the JVM tries to load <file>.aot as a CDS archive. If the loading fails (e.g., we have a mismatch in the classpath), the JVM prints a warning and continues execution without using <file>.aot

[5] When "-XX:AOTCache=<file>.aot -XX:AOTMode=on" are specified, the JVM behaves as if "-Xshare:on -XX:SharedArchiveFile=<file>.aot" are specified. I.e., the JVM tries to load <file>.aot as a CDS archive. If the loading fails (e.g., we have a mismatch in the classpath), the JVM prints an error message and exits.

[6] When -XX:AOTMode=off is specified, the JVM behaves as if "-Xshare:off is specified. No CDS archive will be loaded by the JVM.

[7] When -XX:AOTMode=record is specified, -XX:AOTConfiguration=<file>.aotconfig must be specified and -XX:AOTCache=<file>.aot must NOT be specified. The JVM behaves as if "-Xshare:off -XX:DumpLoadedClassList=<file>.aotconfig" are specified. I.e., we perform a training run and record profiling information into <file>.aotconfig.

[8] When -XX:AOTMode=create is specified, both -XX:AOTConfiguration=<file>.aotconfig and -XX:AOTCache=<file>.aot must be specified. The JVM behaves as if "-Xshare:dump -XX:SharedClassListFile=<file>.aotconfig -XX:SharedArchiveFile=<file>.aot" are specified. I.e., we create the AOT cache <file>.aot using the profiling information stored in <file>.aotconfig.

[9] To avoid confusion, we forbid the simultaneous use of the new flag with the corresponding "old" flags. I.e., if any of the three flags listed above are used in the command-line, then none of the following flags can appear anywhere in the command-line

• -Xshare:on
• -Xshare:auto
• -Xshare:off
• -Xshare:dump
• -XX:DumpLoadedClassList=<file>
• -XX:SharedClassListFile=<file>
• -XX:SharedArchiveFile=<file>