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This document presents information about the -XX command-line options
(parameters) that are specific to Sun Java™ Real-Time System (Java RTS) 2.2 virtual machine.
For a list of the -XX options for the Java HotSpot™ Virtual Machine,
see Java HotSpot VM Options.
Technical Documentation: Links to all the Java RTS technical documents
Introduction
The -XX:+<flag> syntax sets a boolean flag to true, and -XX:-<flag>
sets it to false. For parameters that take values, the syntax is -XX:<param>=<value>.
These parameters are intended for either a production or
a development environment, as indicated in the "Env" column.
Development parameters are available only to the debug version
of the virtual machine (that is, java_g).
Note that certain development parameters
might produce I/O that can change the temporal behavior of the VM.
Caution: Options that are specified with "-XX"
are not stable and are not recommended for casual use.
These options are not part of the official Java API and are subject to change
without notice from one Java RTS release to the other.
The Java RTS command-line options are grouped into the following categories:
Memory-Related Parameters
|
Parameter
|
Default
32/64-bit
|
Env
|
Description
|
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ImmortalSize
|
32M/64M
|
prod
|
The amount of immortal memory to allocate.
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ScopedSize
|
16M/32M
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prod
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The total amount of memory for all scoped memory allocations.
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ScopedMemoryAllocGrain
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16K
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prod
|
The minimum size ScopedMemory area that will be allocated. The value should be a power of two, and if not, it will be rounded down to a power of two.
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RTSJTraceScopeStacks
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false
|
dev
|
Enable tracing of scope stacks. Stacks are printed on changes.
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RTSJEnableImmortalAllocationProbe
|
true
|
prod
|
Enable the immortal-alloc probe of the jrts
DTrace probe provider. This probe fires when immortal memory is
allocated. See the Java RTS DTrace Provider
document.
|
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RTSJShowHeapLayout
|
false
|
prod
|
Show the memory layout.
|
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RTSJLockPagesInMemory
|
true
|
prod
|
Lock pages in memory to avoid swapping to disk.
See Memory Locking section in the Technical Information Guide for more details.
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Thread-Related Parameters
|
Parameter
|
Default
|
Env
|
Description
|
|
RTSJTraceThreading
|
false
|
dev
|
Trace (print) real-time thread scheduling events,
such as thread start and death, priority modification
or boost, blocking on lock, waiting.
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RTSJTraceThreadBinding
|
false
|
prod
|
Trace the binding of threads to processors.
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RTSJBindNHRTToProcessorSet
(Solaris OS only)
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N/A
|
prod
|
Bind NHRTs to the processor set whose ID is specified by the value of the parameter.
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RTSJBindRTTToProcessorSet
(Solaris OS only)
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N/A
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prod
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Bind RTTs to the processor set whose ID is specified by the value of the parameter.
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RTSJBindNHRTToProcessors
(Linux only)
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N/A
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prod
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Bind NHRTs to the specified comma-separated list of processors or to the specified cpuset.
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RTSJBindRTTToProcessors
(Linux only)
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N/A
|
prod
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Bind RTTs to the specified comma-separated list of processors or to the specified cpuset.
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RTSJForceCyclic
(Used only with non-real-time applications.)
(Solaris OS only)
|
Use driver if available; otherwise, fall back to built-in support.
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prod
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Force or prevent usage of the cyclic device driver when running non-real-time applications.
Default (no value specified): Use driver if available; otherwise, fall back to built-in support. Value = true: Use driver if available; otherwise, exit. Value = false: Do not use driver. Use built-in support instead.
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VMStackTraceAtRTSJException
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false
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dev
|
Print stack trace information for an RTSJ-specific exception.
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Access-Related and Assignment Check-Related
Parameters
|
Parameter
|
Default
|
Env
|
Description
|
|
RTSJTraceAccessChecks
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false
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dev
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Enable tracing of access checks. Illegal accesses are reported.
(Used only in interpreted mode.)
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RTSJTraceAssignmentChecks
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false
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dev
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Enable tracing of assignment checks. Illegal assignments are reported.
(Used only in interpreted mode.)
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RTSJIgnoreThrowBoundaryError
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false
|
dev
|
Let an exception escape its scope instead of replacing it.
This allows the developer to dump the stack trace. (See Caution note below.)
|
Caution: If you activate the
RTSJIgnoreThrowBoundaryError flag, do so only temporarily to obtain
information that is hidden because of the replacement of an exception by a
ThrowBoundaryError. Activation of this flag might lead to core dumps or other undefined
behavior since the concerned object might be deleted while it is still in use.
Always disable this option before making a bug report.
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Asynchrony-Related Parameters
|
Parameter
|
Default
|
Env
|
Description
|
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RTSJSignalThreadPriority
|
RTSJMaxPriority
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prod
|
Priority of the thread handling POSIX signals.
See the section "Handlers Released by System Threads"
in the Java RTS Technical Information document.
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RTSJForceHighResTimer
(Solaris OS only)
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Use high-resolution timers if available; otherwise, fall back to regular, low-resolution timers.
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prod
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Force usage of the high-resolution timers.
Default (no value specified): Use high-res timers if available; otherwise, fall back to low-res timers. Value = true: Use high-res timers if user has privileges; otherwise, exit. Value = false: Do not use high-res timers. Use low-res timers instead.
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RTSJHighResTimerThreadPriority
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RTSJMaxPriority
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prod
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Priority of the thread releasing handlers associated with timers.
See the section "Handlers Released by System Threads"
in the Java RTS Technical Information document.
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RTSJDeadlineMonitoringThreadPriority
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RTSJMaxPriority
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prod
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Priority of the system thread responsible for deadline monitoring.
See the section "Handlers Released by System Threads"
in the Java RTS Technical Information document.
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RTSJInitialNumberOfRealtimeServerThread
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2
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prod
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The initial number of server threads created to serve heap-using AsyncEventHandler instances.
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RTSJMaxNumberOfRealtimeServerThread
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100
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prod
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The maximum number of server threads created to serve heap-using AsyncEventHandler instances. If there are more released handlers than server threads then handlers will have to wait for a server thread to become available.
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RTSJInitialNumberOfNoHeapRealtimeServerThread
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2
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prod
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The initial number of server threads created to serve no-heap AsyncEventHandler instances.
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RTSJMaxNumberOfNoHeapRealtimeServerThread
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100
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prod
|
The maximum number of server threads created to serve no-heap AsyncEventHandler instances. If there are more released handlers than server threads then handlers will have to wait for a server thread to become available.
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Compiler-Related Parameters
The table below summarizes the command-line parameters that
are used to control the compilation options for the various thread types.
See the Java RTS Compilation Guide
for a detailed description of how to use these options.
|
Parameter
|
Default
|
Env
|
Description
|
|
ITCJLT
|
false
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prod
|
When true, the ITC policy applies to all java.lang.Thread instances:
- Methods in the precompile list are compiled at class initialization.
- All other methods are JIT compiled.
When false, all java.lang.Thread instances execute code
compiled in JIT mode.
|
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ITCRT
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true
|
prod
|
When true, the ITC policy applies to all javax.realtime.RealtimeThread instances:
- Methods in the precompile list are compiled at class initialization.
- All other methods are JIT compiled
if the JITRT flag is on, or interpreted if the JITRT flag is off.
When false, all RealtimeThread instances execute code compiled in
JIT mode if the JITRT flag is on, or interpreted code if the JITRT flag is off.
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ITCNHRT
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true
|
prod
|
When true, the ITC policy applies to all javax.realtime.NoHeapRealtimeThread instances:
- Methods in the precompile list are compiled at class initialization.
- All other methods are interpreted.
When false, all NoHeapRealtimeThread instances execute interpreted code.
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JITRT
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true
|
prod
|
When true, RealtimeThread instances execute code compiled in JIT mode,
except for methods in the precompile list.
When false, RealtimeThread instances execute interpreted code,
except for methods in the precompile list.
|
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BackgroundCompilation
|
true
|
prod
|
When true, enable background (asynchronous) JIT compilation.
When false, disable background (asynchronous) JIT compilation. This option enables
synchronous compilation. This mode is not recommended
when the RTGC is used. |
|
RTSJBuildCompilationList
|
false
|
prod
|
Instruct the VM to generate a file containing all the
methods that were executed (compiled or interpreted) by a thread
whose execution policy is ITC.
|
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CompilationList
|
nhrt.precompile
|
prod
|
Name of the file containing the results from the RTSJBuildCompilationList option.
|
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RTSJBuildClassInitializationList
|
false
|
prod
|
Instruct the VM to generate a file containing all the classes
that are referenced during the compilation of methods at
initialization. Classes appear in the order in which they were
initialized during the test run.
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PreInitList
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itc.preinit
|
prod
|
Name of the file containing the results from the RTSJBuildClassInitializationList option.
|
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UseITC
|
false
|
prod
|
Force the automatic generation and use of the precompile and preinit lists,
using the default file names.
When true, this option is the equivalent of specifying the following four options
on the command line.
RTSJBuildCompilationList
RTSJBuildClassInitializationList
CompilationList=nhrt.precompile
PreInitList=itc.preinit
|
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PrintCompilation
|
false
|
prod
|
Log JIT-compilation of methods.
|
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PrintITCWarnings
|
false
|
prod
|
Print ITC-related warnings that occur during processing of class and method lists.
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Optimization Parameters
The Java RTS virtual machine can be configured to run with or without
the Real-Time Garbage Collector (RTGC). If the RTGC is not used,
then the default HotSpot serial collector is used.
(The RTGC is enabled by default but can be disabled with the command-line parameter -XX:-UseRTGC.)
Java RTS provides the following command-line options to control the use of
a set of optimizations that impact the trade-off between throughput and determinism.
See the Java RTS Compilation Guide
for a detailed description of how to use these options.
|
Parameter
|
Default
|
Env
|
Description
|
|
UseCHA
|
true
|
prod
|
Use virtual method call inlining.
If an inlining is invalidated because of dynamic class loading, the code is deoptimized.
|
|
JLTCHA
|
true with RTGC
(NA with Serial GC)
|
prod
|
For java.lang.Threads (JLTs) only, use virtual method call inlining when the RTGC is enabled.
(This option is not applicable with the Serial GC.)
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RTTCHA
|
true with RTGC
(NA with Serial GC)
|
prod
|
For RealtimeThreads (RTTs) only, use virtual method call inlining when the RTGC is enabled.
(This option is not applicable with the Serial GC.)
|
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UseInlineCaches
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true with Serial GC
(NA with RTGC)
|
prod
|
Use inline caches when Serial GC is enabled.
(This option is not applicable when the RTGC is enabled.)
|
|
RTSJUseInlineCaches
|
true with RTGC
(NA with Serial GC)
|
prod
|
Use inline caches when RTGC is enabled.
(This option is not applicable when the Serial GC is enabled.)
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Real-Time Garbage Collector-Related Parameters
The following command-line options can be used to tune the activity
of the Real-Time Garbage Collector (RTGC). These options are
categorized by the level of RTGC configuration
that might be needed, depending on application requirements: basic, advanced, and expert.
See the Java RTS Garbage Collection Guide
for a detailed description of how to use these options.
RTGC Basic Options
|
Parameter
|
Default
|
Env
|
Description
|
|
RTGCCriticalReservedBytes
|
0
|
prod
|
Free memory threshold, in bytes, under which only
critical threads can allocate memory. To guarantee determinism, configure this parameter.
See "Tuning the RTGC" in the
Java RTS Garbage Collection Guide.
|
|
RTGCCriticalBoundary
|
OS-dependent
|
prod
|
The priority boundary between critical and non-critical threads.
Threads with priority above this boundary are considered to be critical threads,
while threads with priority at this boundary or below are non-critical threads.
The value defaults to the middle of the
real-time range, which is greater than the default priority for
real-time threads. This default value is OS-dependent, as explained in
"Real-Time Priorities" in the Technical Information document.
|
|
PrintGC
|
false
|
prod
|
Print information gathered whenever the GC runs.
|
|
UseRTGC
|
true
|
prod
|
Use the new real-time garbage collector instead of the
non-real-time, serial collector.
|
RTGC Advanced Options
|
Parameter
|
Default
|
Env
|
Description
|
|
RTGCNormalPriority
|
11
|
prod
|
Normal priority for the RTGC. It defaults to 11 to try
to offer soft real-time behavior for all the real-time threads.
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RTGCNormalWorkers
|
(available CPUs) / 2
|
prod
|
Initial number of parallel RTGC worker threads.
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RTGCBoostedWorkers
|
(available CPUs) / 2
|
prod
|
Boosted number of parallel RTGC worker threads.
|
The number of CPUs available to the RTGC is the number of CPUs available to the VM that have not been specifically assigned to running RealtimeThread or NoHeapRealtimeThread instances. The minimum possible value is one.
RTGC Expert Options
|
Parameter
|
Default
|
Env
|
Description
|
RTGCPrintStatistics |
false |
prod |
Print additional information gathered whenever the RTGC
runs, for advanced tuning or debugging.
|
| RTGCWaitDuration |
10 |
prod |
Number of milliseconds between two consecutive runs of
the RTGC, unless memory is exhausted or an explicit GC is requested. |
UseAnalyticalPolicy |
true |
prod |
When true, use analytical auto-tuning (using statistics) for normal mode.
When false, use "sliding value" auto-tuning for normal mode. |
RTGCTuneBoostedMode |
false |
prod |
When true, turn on auto-tuning ("sliding value") for boosted mode. |
RTGCBoostedPriority |
RTGCCriticalBoundary |
prod |
Priority at which the RTGC activity should execute in order to
guarantee determinism. When free memory falls
below the boosted memory threshold, the RTGC priority is boosted to this level.
If this parameter is not specified, then its default value is the value of
the RTGCCriticalBoundary parameter. |
The following expert-level options are used by both the analytical and the "sliding value" auto-tuning mechanisms for normal mode.
|
Parameter
|
Default
|
Env
|
Description
|
RTGCTargetedMinFreePercent |
5 |
prod |
Minimum free memory level targeted by auto-tuning to start the RTGC in normal mode.
The value is expressed as a percentage of the heap. |
RTGCInitialMinFreePercent |
30 |
prod |
Initial free memory level used by auto-tuning to start the RTGC in normal mode.
The value is expressed as a percentage of the heap. |
RTGCInitialDecreaseFactor |
50 |
prod |
In auto-tuning, the percentage by which to decrease the value of
RTGCInitialMinFreePercent at the end of each GC cycle. |
NormalMinFreeBytes |
0 |
prod |
Minimum (estimated) free heap memory level, in bytes, below which
the RTGC should start its next cycle, at priority RTGCNormalPriority. |
The following expert-level options are used by the "sliding value" auto-tuning mechanism for normal mode.
|
Parameter
|
Default
|
Env
|
Description
|
NormalSlideFactor |
20 |
prod |
Speed at which allocation bursts are forgotten in normal
mode. An integer from 0 to 100, which will be converted to a percentage. |
NormalSafetyMargin |
10 |
prod |
Variation of the allocation rate that is accepted
without creating jitter in normal mode. An integer from 0 to 100, which will be converted to a percentage. |
The following expert-level options are used by the "sliding value" auto-tuning mechanism for boosted mode.
|
Parameter
|
Default
|
Env
|
Description
|
| BoostedMinFreeBytes |
0 |
prod |
Minimum (estimated) free heap memory level, in bytes, below
which the RTGC should be boosted to priority RTGCBoostedPriority. |
| BoostedSlideFactor |
10 |
prod |
Speed at which allocation bursts are forgotten in
boosted mode. An integer from 0 to 100, which will be converted to a percentage. |
BoostedSafetyMargin |
20 |
prod |
Variation of the allocation rate that is accepted
without creating jitter in boosted mode. An integer from 0 to 100, which will be converted to a percentage. |
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DTrace Provider-Related Parameters (Solaris OS Only)
The table below summarizes the command-line parameters that are used in conjunction with the
jrts DTrace Provider.
See the Java RTS DTrace Provider Guide
for a detailed description on how to use these options.
|
Parameter
|
Default
|
Env
|
Description
|
|
PauseAtStartup
|
false
|
prod
|
Instructs the VM to pause execution until after the file specified by PauseAtStartupFile has been deleted.
|
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PauseAtStartupFile
|
vm.paused.<pid_of_paused_vm>
|
prod
|
The file used in conjunction with PauseAtStartup.
|
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RTSJEnableImmortalAllocationProbe
|
true
|
prod
|
Enable the immortal-alloc probe of the jrts
DTrace probe provider. This probe fires when immortal memory is
allocated.
|
|
RTSJEnableInterpreterMethodEntryProbe
|
false
|
prod
|
Enable the interpreting-method probe of the jrts
DTrace probe provider. This probe fires when a thread starts executing a method
using the interpreter.
|
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Other Parameters
|
Parameter
|
Default
|
Env
|
Description
|
|
RTSJEnableServerThreadNamingProbe
|
false
|
prod
|
Activate the firing of the thread-set-name probe during the binding and unbinding process.
|
|
RTSJDisableAtomicThreadDump
|
true
|
prod
|
Disable the suspension of execution. Set to true in prod enviroment.
When this parameter is set to false,
Java RTS suspends application execution in order to obtain thread
stack information (for debugging in dev environment).
|
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RTSJNumRTPrio
|
OS-dependent
|
prod
|
The number of real-time priorities used by Java RTS.
See explanation in "Real-Time Priorities"
in the Technical Information document.
|
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VMStackTraceAtRTSJException
|
false
|
dev
|
Print a VM stack trace when an RTSJ exception occurs.
|
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RTSJIgnoreThrowBoundaryError
|
false
|
dev
|
Use this parameter only temporarily to obtain information that is hidden
because of the replacement of an exception by a ThrowBoundaryError.
Caution: Activation of this flag might lead to core dumps or other undefined behavior
since the concerned object might be deleted while it is still in use.
|
|
LogJitterProneEvents
|
false
|
prod
|
Produce a file named hs_jitter_pid<pid>.log containing several time-stamped events,
including class initialization, method interpretation, failed allocation for a critical thread, etc.
See "Command-Line Options" section in the Tools, Tuning, and Troubleshooting Guide.
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Copyright © 2009 Sun Microsystems, Inc. All Rights Reserved.
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