RFR: 8259070: Add jcmd option to dump CDS [v8]

[Ioi Lam]

On Wed, 31 Mar 2021 20:58:46 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 pull request now contains 10 commits:
> 
>  - Fix revert unintentionally comment, merge master.
>  - Merge branch 'master' of ssh://github.com/yminqi/jdk into jdk-8259070
>  - Remove CDS.getVMArguments, changed to use VM.getRuntimeVMArguments. Removed unused function from ClassLoader. Improved InstanceKlass::is_shareable() and related test. Added more test scenarios.
>  - Remove redundant check for if a class is shareable
>  - Fix according to review comment and add more tests
>  - 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/services/diagnosticCommand.cpp line 1106:

> 1104:     output()->print_cr("Dynamic dump:");
> 1105:     if (!UseSharedSpaces) {
> 1106:       output()->print_cr("CDS is not available for the JDK");

I think we should use a message similar to this:

$ java -Xshare:off -XX:ArchiveClassesAtExit=xxx -version
Error occurred during initialization of VM
DynamicDumpSharedSpaces is unsupported when base CDS archive is not loaded

How about "dynamic_dump is unsupported when base CDS archive is not loaded".

src/hotspot/share/services/diagnosticCommand.cpp line 1125:

> 1123:   Symbol* cds_name  = vmSymbols::jdk_internal_misc_CDS();
> 1124:   Klass*  cds_klass = SystemDictionary::resolve_or_fail(cds_name, true /*throw error*/,  CHECK);
> 1125:   JavaValue result(T_OBJECT);

Should be `result(T_VOID)` to match the signature of `CDS.dumpSharedArchive()`

src/hotspot/share/services/diagnosticCommand.cpp line 1133:

> 1131:                          vmSymbols::dumpSharedArchive(),
> 1132:                          vmSymbols::dumpSharedArchive_signature(),
> 1133:                          &args, THREAD);

Should be `&args, CHECK);`. Recently, we have started to to avoid using `THREAD` if the  callee function may throw an exception.

src/java.base/share/classes/jdk/internal/misc/CDS.java line 218:

> 216:         try {
> 217:             PrintStream prt = new PrintStream(fileName);
> 218:             prt.println("Command:");

[Try-with-resources](https://docs.oracle.com/javase/tutorial/essential/exceptions/tryResourceClose.html) should be used to make sure the streams are closed when the method exits (normally or on exception).

try (InputStreamReader isr = new InputStreamReader(stream);
     BufferedReader rdr = new BufferedReader(isr);
     PrintStream prt = new PrintStream(fileName);)
{
    prt.println("Command:"); ....

src/java.base/share/classes/jdk/internal/misc/CDS.java line 307:

> 305:                     outputStdStream(proc.getErrorStream(), stdErrFile, cmds);
> 306:                 }).start();
> 307: 

I think the above code can be refactored to avoid duplication. Something like:

String stdOutFile = drainOutput(proc.getInputStream(), "stdout");
String stdErrFile = drainOutput(proc.getErrorStream(), "stderr");

and move the common code into drainOutput().

-------------

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