Summary

Deprecate the seldomly used flags related to CDS: UseSharedSpace, RequireSharedSpaces, DumpSharedSpaces, and DynamicSharedSpaces options.

Problem

Users should not be using the -XX:+UseSharedSpace, -XX:+RequireSharedSpaces, and -XX:+DumpSharedSpaces options. Instead, they should use the options -Xshare:off, -Xshare:auto, -Xshare:on, and -Xshare:dump, which are documented in https://docs.oracle.com/en/java/javase/17/vm/class-data-sharing.html

The -XX:+DynamicDumpSharedSpaces is useless because it is always overridden by the command line processing in Arguments::finalize_vm_init_args(). The feature related to the DynamicDumpSharedSpaces should be accessed using the -XX:ArchiveClassesAtExit option.

Solution

The solution is to deprecate these four command line options and eventually remove them.

Specification

Deprecating these options involves the following code change to arguments.cpp:

--- a/src/hotspot/share/runtime/arguments.cpp
+++ b/src/hotspot/share/runtime/arguments.cpp
@@ -528,6 +528,8 @@ static SpecialFlag const special_jvm_flags[] = {
   { "FlightRecorder",               JDK_Version::jdk(13), JDK_Version::undefined(), JDK_Version::undefined() },
   { "FilterSpuriousWakeups",        JDK_Version::jdk(18), JDK_Version::jdk(19), JDK_Version::jdk(20) },
   { "MinInliningThreshold",         JDK_Version::jdk(18), JDK_Version::jdk(19), JDK_Version::jdk(20) },
+  { "UseSharedSpace",               JDK_Version::jdk(18), JDK_Version::jdk(19), JDK_Version::jdk(20) },
+  { "RequireSharedSpaces",          JDK_Version::jdk(18), JDK_Version::jdk(19), JDK_Version::jdk(20) },
+  { "DumpSharedSpaces",             JDK_Version::jdk(18), JDK_Version::jdk(19), JDK_Version::jdk(20) },
+  { "DynamicDumpSharedSpaces",      JDK_Version::jdk(18), JDK_Version::jdk(19), JDK_Version::jdk(20) },

The flags are defined here. This code will be removed when the flags are removed:

  product(bool, UseSharedSpaces, true,                                      \
      "Use shared spaces for metadata")                                     \

  product(bool, RequireSharedSpaces, false,                                 \
      "Require shared spaces for metadata")                                 \

  product(bool, DumpSharedSpaces, false,                                    \
          "Special mode: JVM reads a class list, loads classes, builds "    \
          "shared spaces, and dumps the shared spaces to a file to be "     \
          "used in future JVM runs")                                        \

 product(bool, DynamicDumpSharedSpaces, false,                              \
          "Dynamic archive")                                                \