RFR: 8259070: Add jcmd option to dump CDS [v4]

[Ioi Lam]

On Thu, 11 Mar 2021 04:03:29 GMT, Yumin Qi <minqi at openjdk.org> wrote:

>> Hi, Please review
>> 
>>   Added jcmd option for dumping CDS archive during application runtime. Before this change, user has to dump shared archive in two steps: first run application with
>>   `java -XX:DumpLoadedClassList=<classlist> .... `  
>>  to collect shareable class names and saved in file `<classlist>` , then 
>>   `java -Xshare:dump -XX:SharedClassListFile=<classlist> -XX:SharedArchiveFile=<archivefile> ...`
>>   With this change, user can use jcmd to dump CDS without going through above steps. Also user can choose a moment during the app runtime  to dump an archive.
>>    The bug is associated with the CSR: https://bugs.openjdk.java.net/browse/JDK-8259798 which has been approved.
>>    New added jcmd option:
>>    `jcmd <pid or AppName> VM.cds static_dump <filename>`
>>    or
>>     `jcmd <pid or AppName> VM.cds dynamic_dump <filename>`
>>   To dump dynamic archive, requires start app with newly added flag `-XX:+RecordDynamicDumpInfo`, with this flag, some information related to dynamic dump like loader constraints will be recorded. Note the dumping process changed some object memory locations so for dumping dynamic archive, can only done once for a running app. For static dump, user can dump multiple times against same process. 
>>    The file name is optional, if the file name is not supplied, the file name will take format of `java_pid<number>_static.jsa` or `java_pid<number>_dynamic.jsa` for static and dynamic respectively. The `<number>` is the application process ID.
>> 
>>   Tests: tier1,tier2,tier3,tier4
>> 
>> Thanks
>> Yumin
>
> Yumin Qi has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains five additional commits since the last revision:
> 
>  - Fix filter more flags to exclude in static dump, add more test cases
>  - Merge branch 'master' into jdk-8259070
>  - Fix white space in CDS.java
>  - Add function CDS.dumpSharedArchive in java to dump shared archive
>  - 8259070: Add jcmd option to dump CDS

Changes requested by iklam (Reviewer).

src/hotspot/share/memory/metaspaceShared.cpp line 50:

> 48: #include "memory/cppVtables.hpp"
> 49: #include "memory/dumpAllocStats.hpp"
> 50: #include "memory/dynamicArchive.hpp"

This is not needed anymore.

src/hotspot/share/prims/jvm.cpp line 3766:

> 3764: JVM_ENTRY(void, JVM_DumpDynamicArchive(JNIEnv *env, jstring archiveName))
> 3765: #if INCLUDE_CDS
> 3766:   assert(UseSharedSpaces && RecordDynamicDumpInfo, "Sanity check");

I think the message should say why this is true.

How about `assert(UseSharedSpaces && RecordDynamicDumpInfo, "already checked in arguments.cpp");`?

(same for the next assert statement at line 3774)

src/hotspot/share/services/diagnosticCommand.cpp line 1139:

> 1137:     Handle throwable(THREAD, PENDING_EXCEPTION);
> 1138:     CLEAR_PENDING_EXCEPTION;
> 1139:     java_lang_Throwable::print_stack_trace(throwable, output());

Actually, it's not necessary to print the stack trace here. This function is called by `jcmd` in attachListener.cpp which will print the stack trace for you.

static jint jcmd(AttachOperation* op, outputStream* out) {
  Thread* THREAD = Thread::current();
  // All the supplied jcmd arguments are stored as a single
  // string (op->arg(0)). This is parsed by the Dcmd framework.
  DCmd::parse_and_execute(DCmd_Source_AttachAPI, out, op->arg(0), ' ', THREAD);
  if (HAS_PENDING_EXCEPTION) {
    java_lang_Throwable::print(PENDING_EXCEPTION, out);
    out->cr();
    CLEAR_PENDING_EXCEPTION;
    return JNI_ERR;
  }
  return JNI_OK;
}

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PR: https://git.openjdk.java.net/jdk/pull/2737