Make several HotSpot flags manageable

[Srinivas Ramakrishna]

There are a bunch of Hotspot flags (several of them in GC, but also non-GC
ones) that switch on various printing options.
These started out historically as product flags but it might make sense to
make them manageable to allow greater field
serviceability of the VM in order to manually switch on verbose print
options for debugging running JVM operation.
If there is interest, I'd like to open (if one isn't already open) a bug on
openjdk bugzilla and offer a patch.

A prime example is SafepointDelay and PrintSafepointDelay, but there are a
whole bunch of more such options, for example,
the following from a syntactic filter to catch a sample. The idea isn't to
only touch those flags which control the emission
of logging/stats from the jvm, not alter its behaviour otherwise in any
manner.

Is there appetite for this kind of change? In most cases nothing would be
needed other than to flip the flag from product to
manageable. In other cases, one would need to make sure to use a
periodically taken snapshot of the flag to allow cosistency
in the work done in various routines involved in one "round" of
logging/stats.

The following is a syntactic sample, and more work would be needed to go
over these flags and others to determine the specific
change needed. I plan to do that and produce the patch once there is some
agreement that this would be a positive step.

Please let me know your thoughts/reactions/comments etc., but it would
improve HotSpot's field debuggability/serviceability story
by quite a bit to do this.

thanks, and have a good weekend!
-- ramki (openjdk: ysr)

% $currentjdk/bin/java -XX:+PrintFlagsFinal -version | grep -v manag | grep
-i print

     bool CMSPrintChunksInDump                      = false
              {product}

     bool CMSPrintEdenSurvivorChunks                = false
              {product}

     bool CMSPrintObjectsInDump                     = false
              {product}

     bool PrintAdaptiveSizePolicy                   = false
              {product}

     bool PrintCMSInitiationStatistics              = false
              {product}

     intx PrintCMSStatistics                        = 0
              {product}

     bool PrintCodeCache                            = false
              {product}

     bool PrintCodeCacheOnCompilation               = false
              {product}

     bool PrintCommandLineFlags                     = false
              {product}

     bool PrintCompilation                          = false
              {product}

     intx PrintFLSCensus                            = 0
              {product}

     intx PrintFLSStatistics                        = 0
              {product}

     bool PrintFlagsFinal                          := true
              {product}

     bool PrintFlagsInitial                         = false
              {product}

     bool PrintGCApplicationConcurrentTime          = false
              {product}

     bool PrintGCApplicationStoppedTime             = false
              {product}

     bool PrintGCCause                              = true
              {product}

     bool PrintGCTaskTimeStamps                     = false
              {product}

     bool PrintHeapAtGC                             = false
              {product rw}

     bool PrintHeapAtGCExtended                     = false
              {product rw}

     bool PrintHeapAtSIGBREAK                       = true
              {product}

     bool PrintJNIGCStalls                          = false
              {product}

     bool PrintJNIResolving                         = false
              {product}

     bool PrintOldPLAB                              = false
              {product}

     bool PrintOopAddress                           = false
              {product}

     bool PrintPLAB                                 = false
              {product}

     bool PrintParallelOldGCPhaseTimes              = false
              {product}

     bool PrintPromotionFailure                     = false
              {product}

     bool PrintReferenceGC                          = false
              {product}

     bool PrintSafepointStatistics                  = false
              {product}

     intx PrintSafepointStatisticsCount             = 300
              {product}

     intx PrintSafepointStatisticsTimeout           = -1
              {product}

     bool PrintSharedSpaces                         = false
              {product}

     bool PrintStringDeduplicationStatistics        = false
              {product}

     bool PrintStringTableStatistics                = false
              {product}

     bool PrintTLAB                                 = false
              {product}

     bool PrintTenuringDistribution                 = false
              {product}

     bool PrintTieredEvents                         = false
              {product}

     bool PrintVMOptions                            = false
              {product}

     bool PrintVMQWaitTime                          = false
              {product}

     bool PrintWarnings                             = true
              {product}

     bool ProfilerPrintByteCodeStatistics           = false
              {product}


I know not all of the following or those above can necessarily be made
manageable, but this is a possible

starting point for the work/investigation.....

% $currentjdk/bin/java -XX:+PrintFlagsFinal -version | grep -v manag | grep
-i trace | grep produc

...

     intx BCEATraceLevel                            = 0
              {product}

     bool DTraceAllocProbes                         = false
              {product}

     bool DTraceMethodProbes                        = false
              {product}

     bool DTraceMonitorProbes                       = false
              {product}

     bool ExtendedDTraceProbes                      = false
              {product}

     bool JavaMonitorsInStackTrace                  = true
              {product}

     intx MaxJavaStackTraceDepth                    = 1024
              {product}

     bool OmitStackTraceInFastThrow                 = true
              {product}

     bool StackTraceInThrowable                     = true
              {product}

     bool TraceBiasedLocking                        = false
              {product}

     bool TraceClassLoading                         = false
              {product rw}

     bool TraceClassLoadingPreorder                 = false
              {product}

     bool TraceClassResolution                      = false
              {product}

     bool TraceClassUnloading                       = false
              {product rw}

     bool TraceDynamicGCThreads                     = false
              {product}

     bool TraceGen0Time                             = false
              {product}

     bool TraceGen1Time                             = false
              {product}

    ccstr TraceJVMTI                                =
              {product}

     bool TraceLoaderConstraints                    = false
              {product rw}

     bool TraceMetadataHumongousAllocation          = false
              {product}

     bool TraceMonitorInflation                     = false
              {product}

     bool TraceParallelOldGCTasks                   = false
              {product}

     intx TraceRedefineClasses                      = 0
              {product}

     bool TraceSafepointCleanupTime                 = false
              {product}

     bool TraceSuspendWaitFailures                  = false
              {product}