RFR: 8193513: add support for printing a stack trace on class loading [v2]

[Johan Sjölen]

On Tue, 20 Jun 2023 09:44:41 GMT, Doug Simon <dnsimon at openjdk.org> wrote:

>> In the development of libgraal, it has been very useful to see why a given class is loaded (e.g., trying to reduce startup time by avoiding unnecessary eager class loading). One way to do this is to see the stack trace when the VM loads a class. The only possibility currently is to add a static initializer to the class of interest. However, not only is this not always possible but it doesn't correlate with class loading but with class initialization.
>> 
>> This PR proposes a `TraceClassLoadingCause` VM flag:
>> 
>> 
>>   product(ccstr, TraceClassLoadingCause, nullptr, DIAGNOSTIC,               \
>>           "Print a stack trace when loading a class whose fully"            \
>>           "qualified name contains this string ("*" matches "             \
>>           "any class).")                                                    \
>> 
>> 
>> I would have liked to implement this using Unified Logging but UL has no support for filtering on the class names.
>> 
>> Example usage:
>> 
>> java -XX:+UnlockDiagnosticVMOptions -XX:TraceClassLoadingCause=Thread --version
>> Loading java.lang.Thread
>> Loading java.lang.Thread$FieldHolder
>> Loading java.lang.Thread$Constants
>> Loading java.lang.Thread$UncaughtExceptionHandler
>> Loading java.lang.ThreadGroup
>> Loading java.lang.BaseVirtualThread
>> Loading java.lang.VirtualThread
>> Loading java.lang.ThreadBuilders$BoundVirtualThread
>> Loading java.lang.Thread$State
>> 	at jdk.internal.misc.VM.toThreadState(java.base/VM.java:336)
>> 	at java.lang.Thread.threadState(java.base/Thread.java:2731)
>> 	at java.lang.Thread.isTerminated(java.base/Thread.java:2738)
>> 	at java.lang.Thread.getThreadGroup(java.base/Thread.java:1957)
>> 	at java.lang.ref.Reference$1.startThreads(java.base/Reference.java:314)
>> 	at java.lang.System.initPhase1(java.base/System.java:2206)
>> Loading java.lang.Thread$ThreadIdentifiers
>> 	at java.lang.Thread.<init>(java.base/Thread.java:734)
>> 	at java.lang.Thread.<init>(java.base/Thread.java:1477)
>> 	at java.lang.ref.Reference$ReferenceHandler.<init>(java.base/Reference.java:198)
>> 	at java.lang.ref.Reference.startReferenceHandlerThread(java.base/Reference.java:300)
>> 	at java.lang.ref.Reference$1.startThreads(java.base/Reference.java:318)
>> 	at java.lang.System.initPhase1(java.base/System.java:2206)
>> Loading java.lang.ref.Finalizer$FinalizerThread
>> 	at java.lang.ref.Finalizer.startFinalizerThread(java.base/Finalizer.java:187)
>> 	at java.lang.ref.Reference$1.startThreads(java.base/Reference.java:319)
>> 	at java.lang.Sy...
>
> Doug Simon has refreshed the contents of this pull request, and previous commits have been removed. The incremental views will show differences compared to the previous content of the PR. The pull request contains one new commit since the last revision:
> 
>   added TraceClassLoadingCause flag

src/hotspot/share/oops/instanceKlass.cpp line 3745:

> 3743:       (strcmp(TraceClassLoadingCause, "*") == 0 || strstr(external_name(), TraceClassLoadingCause) != nullptr))
> 3744:   {
> 3745:     stringStream st;

Please use `LogMessage` and `NonInterleavingLogStream` when this is replaced with UL.  See `test_logstream.cpp:117` for usage example.

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

PR Review Comment: https://git.openjdk.org/jdk/pull/14553#discussion_r1246357514