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 This document describes system properties that are used for internal

 debugging and instrumentation purposes, along with the system loggers,

 which are used for the same thing.

 This document is intended as a developer resource, and it is not

 needed as Nashorn documentation for normal usage. Flags and system

 properties described herein are subject to change without notice.

 =====================================

 1. System properties used internally

 =====================================

 This documentation of the system property flags assume that the

 default value of the flag is false, unless otherwise specified.

 SYSTEM PROPERTY: -Dnashorn.args=<string>

 This property takes as its value a space separated list of Nashorn

 command line options that should be passed to Nashorn. This might be

 useful in environments where it is hard to tell how a nashorn.jar is

 launched.

 Example:

 > java -Dnashorn.args="--lazy-complation --log=compiler" large-java-app-with-nashorn.jar 

 > ant -Dnashorn.args="--log=codegen" antjob

 SYSTEM PROPERTY: -Dnashorn.args.prepend=<string>

 This property behaves like nashorn.args, but adds the given arguments

 before the existing ones instead of after them. Later arguments will

 overwrite earlier ones, so this is useful for setting default arguments

 that can be overwritten.

 SYSTEM PROPERTY: -Dnashorn.unstable.relink.threshold=x

 This property controls how many call site misses are allowed before a 

 callsite is relinked with "apply" semantics to never change again. 

 In the case of megamorphic callsites, this is necessary, or the 

 program would spend all its time swapping out callsite targets. Dynalink 

 has a default value (currently 8 relinks) for this property if it 

 is not explicitly set.

 SYSTEM PROPERTY: -Dnashorn.compiler.splitter.threshold=x

 This will change the node weight that requires a subgraph of the IR to

 be split into several classes in order not to run out of bytecode space.

 The default value is 0x8000 (32768).

 SYSTEM PROPERTY: -Dnashorn.serialize.compression=<x>

 This property sets the compression level used when deflating serialized

 AST structures of anonymous split functions. Valid values range from 0 to 9,

 the default value is 4. Higher values will reduce memory size of serialized

 AST but increase CPU usage required for compression.

 SYSTEM PROPERTY: -Dnashorn.codegen.debug.trace=<x>

 See the description of the codegen logger below.

 SYSTEM PROPERTY: -Dnashorn.fields.objects, -Dnashorn.fields.dual

 When the nashorn.fields.objects property is true, Nashorn will always

 use object fields for AccessorProperties, requiring boxing for all

 primitive property values. When nashorn.fields.dual is set, Nashorn

 will always use dual long/object fields, which allows primitives to be

 stored without boxing. When neither system property is set, Nashorn

 chooses a setting depending on the optimistic types setting (dual

 fields when optimistic types are enabled, object-only fields otherwise).

 With dual fields, Nashorn uses long fields to store primitive values.

 Ints are represented as the 32 low bits of the long fields. Doubles

 are represented as the doubleToLongBits of their value. This way a

 single field can be used for all primitive types. Packing and

 unpacking doubles to their bit representation is intrinsified by

 the JVM and extremely fast.

 In the future, this might complement or be replaced by experimental

 feature sun.misc.TaggedArray, which has been discussed on the mlvm

 mailing list. TaggedArrays are basically a way to share data space

 between primitives and references, and have the GC understand this.

 SYSTEM PROPERTY: -Dnashorn.compiler.symbol.trace=[<x>[,*]], 

   -Dnashorn.compiler.symbol.stacktrace=[<x>[,*]]

 When this property is set, creation and manipulation of any symbol

 named "x" will show information about when the compiler changes its

 type assumption, bytecode local variable slot assignment and other

 data. This is useful if, for example, a symbol shows up as an Object,

 when you believe it should be a primitive. Usually there is an

 explanation for this, for example that it exists in the global scope

 and type analysis has to be more conservative. 

 Several symbols names to watch can be specified by comma separation.

 If no variable name is specified (and no equals sign), all symbols

 will be watched

 By using "stacktrace" instead of or together with "trace", stack

 traces will be displayed upon symbol changes according to the same

 semantics.

 SYSTEM PROPERTY: -Dnashorn.lexer.xmlliterals

 If this property it set, it means that the Lexer should attempt to

 parse XML literals, which would otherwise generate syntax

 errors. Warning: there are currently no unit tests for this

 functionality.

 XML literals, when this is enabled, end up as standard LiteralNodes in

 the IR.

 SYSTEM_PROPERTY: -Dnashorn.debug

 If this property is set to true, Nashorn runs in Debug mode. Debug

 mode is slightly slower, as for example statistics counters are enabled

 during the run. Debug mode makes available a NativeDebug instance

 called "Debug" in the global space that can be used to print property

 maps and layout for script objects, as well as a "dumpCounters" method

 that will print the current values of the previously mentioned stats

 counters.

 These functions currently exists for Debug:

 "map" - print(Debug.map(x)) will dump the PropertyMap for object x to

 stdout (currently there also exist functions called "embedX", where X

 is a value from 0 to 3, that will dump the contents of the embed pool

 for the first spill properties in any script object and "spill", that

 will dump the contents of the growing spill pool of spill properties

 in any script object. This is of course subject to change without

 notice, should we change the script object layout.

 "methodHandle" - this method returns the method handle that is used

 for invoking a particular script function.

 "identical" - this method compares two script objects for reference

 equality. It is a == Java comparison

 "equals" - Returns true if two objects are either referentially

 identical or equal as defined by java.lang.Object.equals.

 "dumpCounters" - will dump the debug counters' current values to

 stdout.

 Currently we count number of ScriptObjects in the system, number of

 Scope objects in the system, number of ScriptObject listeners added,

 removed and dead (without references).

 We also count number of ScriptFunctions, ScriptFunction invocations

 and ScriptFunction allocations.

 Furthermore we count PropertyMap statistics: how many property maps

 exist, how many times were property maps cloned, how many times did

 the property map history cache hit, prevent new allocations, how many

 prototype invalidations were done, how many time the property map

 proto cache hit.

 Finally we count callsite misses on a per callsite bases, which occur

 when a callsite has to be relinked, due to a previous assumption of

 object layout being invalidated.

 "getContext" - return the current Nashorn context.

 "equalWithoutType" - Returns true if if the two objects are both

 property maps, and they have identical properties in the same order,

 but allows the properties to differ in their types.

 "diffPropertyMaps" Returns a diagnostic string representing the difference

 of two property maps.

 "getClass" - Returns the Java class of an object, or undefined if null.

 "toJavaString" - Returns the Java toString representation of an object.

 "toIdentString" - Returns a string representation of an object consisting

 of its java class name and hash code.

 "getListenerCount" - Return the number of property listeners for a

 script object.

 "getEventQueueCapacity" - Get the capacity of the event queue.

 "setEventQueueCapacity" - Set the event queue capacity.

 "addRuntimeEvent" - Add a runtime event to the runtime event queue.

 The queue has a fixed size (see -Dnashorn.runtime.event.queue.size)

 and the oldest entry will be thrown out of the queue is about to overflow.

 "expandEventQueueCapacity" - Expands the event queue capacity,

 or truncates if capacity is lower than current capacity. Then only

 the newest entries are kept.

 "clearRuntimeEvents" - Clear the runtime event queue.

 "removeRuntimeEvent" - Remove a specific runtime event from the event queue.

 "getRuntimeEvents" - Return all runtime events in the queue as an array.

 "getLastRuntimeEvent" - Return the last runtime event in the queue.

 SYSTEM PROPERTY: -Dnashorn.methodhandles.debug.stacktrace

 This enhances methodhandles logging (see below) to also dump the

 stack trace for every instrumented method handle operation.

 Warning: This is enormously verbose, but provides a pretty

 decent "grep:able" picture of where the calls are coming from.

 SYSTEM PROPERTY: -Dnashorn.cce

 Setting this system property causes the Nashorn linker to rely on

 ClassCastExceptions for triggering a callsite relink. If not set, the linker

 will add an explicit instanceof guard.

 SYSTEM PROPERTY: -Dnashorn.spill.threshold=<x>

 This property sets the number of fields in an object from which to use

 generic array based spill storage instead of Java fields. The default value

 is 256.

 SYSTEM PROPERTY: -Dnashorn.tcs.miss.samplePercent=<x>

 When running with the trace callsite option (-tcs), Nashorn will count

 and instrument any callsite misses that require relinking. As the

 number of relinks is large and usually produces a lot of output, this

 system property can be used to constrain the percentage of misses that

 should be logged. Typically this is set to 1 or 5 (percent). 1% is the

 default value.

 SYSTEM PROPERTY: -Dnashorn.persistent.code.cache

 This property can be used to set the directory where Nashorn stores

 serialized script classes generated with the -pcc/--persistent-code-cache

 option. The default directory name is "nashorn_code_cache".

 SYSTEM PROPERTY: -Dnashorn.typeInfo.maxFiles

 Maximum number of files to store in the type info cache. The type info cache

 is used to cache type data of JavaScript functions when running with

 optimistic types (-ot/--optimistic-types). There is one file per JavaScript

 function in the cache.

 The default value is 0 which means the feature is disabled. Setting this

 to something like 20000 is probably good enough for most applications and

 will usually cap the cache directory to about 80MB presuming a 4kB

 filesystem allocation unit. Set this to "unlimited" to run without limit.

 If the value is not 0 or "unlimited", Nashorn will spawn a cleanup thread

 that makes sure the number of files in the cache does not exceed the given

 value by deleting the least recently modified files.

 SYSTEM PROPERTY: -Dnashorn.typeInfo.cacheDir

 This property can be used to set the directory where Nashorn stores the

 type info cache when -Dnashorn.typeInfo.maxFiles is set to a nonzero

 value. The default location is platform specific. On Windows, it is

 "${java.io.tmpdir}\com.oracle.java.NashornTypeInfo". On Linux and

 Solaris it is "~/.cache/com.oracle.java.NashornTypeInfo". On Mac OS X,

 it is "~/Library/Caches/com.oracle.java.NashornTypeInfo".

 SYSTEM PROPERTY: -Dnashorn.typeInfo.cleanupDelaySeconds=<value>

 This sets the delay between cleanups of the typeInfo cache, in seconds.

 The default delay is 20 seconds.

 SYSTEM PROPERTY: -Dnashorn.profilefile=<filename>

 When running with the profile callsite options (-pcs), Nashorn will

 dump profiling data for all callsites to stderr as a shutdown hook. To

 instead redirect this to a file, specify the path to the file using

 this system property.

 SYSTEM_PROPERTY: -Dnashorn.regexp.impl=[jdk|joni]

 This property defines the regular expression engine to be used by

 Nashorn. Set this flag to "jdk" to get an implementation based on the

 JDK's java.util.regex package. Set this property to "joni" to install

 an implementation based on Joni, the regular expression engine used by

 the JRuby project. The default value for this flag is "joni"

 SYSTEM PROPERTY: -Dnashorn.runtime.event.queue.size=<value>

 Nashorn provides a fixed sized runtime event queue for debugging purposes.

 See -Dnashorn.debug for methods to access the event queue.

 The default value is 1024.

 ===============

 2. The loggers.

 ===============

 It is very simple to create your own logger. Use the DebugLogger class

 and give the subsystem name as a constructor argument.

 The Nashorn loggers can be used to print per-module or per-subsystem

 debug information with different levels of verbosity. The loggers for

 a given subsystem are available are enabled by using

 --log=<systemname>[:<level>]

 on the command line.

 Here <systemname> identifies the name of the subsystem to be logged

 and the optional colon and level argument is a standard

 java.util.logging.Level name (severe, warning, info, config, fine,

 finer, finest). If the level is left out for a particular subsystem,

 it defaults to "info". Any log message logged as the level or a level

 that is more important will be output to stderr by the logger.

 Several loggers can be enabled by a single command line option, by

 putting a comma after each subsystem/level tuple (or each subsystem if

 level is unspecified). The --log option can also be given multiple

 times on the same command line, with the same effect.

 For example: --log=codegen,fields:finest is equivalent to

 --log=codegen:info --log=fields:finest

 The following is an incomplete list of subsystems that currently

 support logging. Look for classes implementing

 jdk.nashorn.internal.runtime.logging.Loggable for more loggers.

 * compiler

 The compiler is in charge of turning source code and function nodes

 into byte code, and installs the classes into a class loader

 controlled from the Context. Log messages are, for example, about

 things like new compile units being allocated. The compiler has global

 settings that all the tiers of codegen (e.g. Lower and CodeGenerator)

 use.s

 * recompile

 This logger shows information about recompilation of scripts and

 functions at runtime. Recompilation may happen because a function

 was called with different parameter types, or because an optimistic

 assumption failed while executing a function with -ot/--optimistic-types.

 * codegen

 The code generator is the emitter stage of the code pipeline, and

 turns the lowest tier of a FunctionNode into bytecode. Codegen logging

 shows byte codes as they are being emitted, line number information

 and jumps. It also shows the contents of the bytecode stack prior to

 each instruction being emitted. This is a good debugging aid. For

 example:

 [codegen] #41                       line:2 (f)_afc824e 

 [codegen] #42                           load symbol x slot=2 

 [codegen] #43  {1:O}                    load int 0 

 [codegen] #44  {2:I O}                  dynamic_runtime_call GT:ZOI_I args=2 returnType=boolean 

 [codegen] #45                              signature (Ljava/lang/Object;I)Z 

 [codegen] #46  {1:Z}                    ifeq  ternary_false_5402fe28 

 [codegen] #47                           load symbol x slot=2 

 [codegen] #48  {1:O}                    goto ternary_exit_107c1f2f 

 [codegen] #49                       ternary_false_5402fe28 

 [codegen] #50                           load symbol x slot=2 

 [codegen] #51  {1:O}                    convert object -> double 

 [codegen] #52  {1:D}                    neg 

 [codegen] #53  {1:D}                    convert double -> object 

 [codegen] #54  {1:O}                ternary_exit_107c1f2f 

 [codegen] #55  {1:O}                    return object 

 shows a ternary node being generated for the sequence "return x > 0 ?

 x : -x"

 The first number on the log line is a unique monotonically increasing

 emission id per bytecode. There is no guarantee this is the same id

 between runs.  depending on non deterministic code

 execution/compilation, but for small applications it usually is. If

 the system variable -Dnashorn.codegen.debug.trace=<x> is set, where x

 is a bytecode emission id, a stack trace will be shown as the

 particular bytecode is about to be emitted. This can be a quick way to

 determine where it comes from without attaching the debugger. "Who

 generated that neg?"

 The --log=codegen option is equivalent to setting the system variable

 "nashorn.codegen.debug" to true.

 * fold

 Shows constant folding taking place before lowering

 * lower

 This is the first lowering pass.

 Lower is a code generation pass that turns high level IR nodes into

 lower level one, for example substituting comparisons to RuntimeNodes

 and inlining finally blocks.

 Lower is also responsible for determining control flow information

 like end points.

 * symbols

 The symbols logger tracks the assignment os symbols to identifiers.

 * scopedepths

 This logs the calculation of scope depths for non-local symbols.

 * fields

 The --log=fields option (at info level) is equivalent to setting the

 system variable "nashorn.fields.debug" to true. At the info level it

 will only show info about type assumptions that were invalidated. If

 the level is set to finest, it will also trace every AccessorProperty

 getter and setter in the program, show arguments, return values

 etc. It will also show the internal representation of respective field

 (Object in the normal case, unless running with the dual field

 representation)

 * time

 This enables timers for various phases of script compilation. The timers

 will be dumped when the Nashorn process exits. We see a percentage value

 of how much time was spent not executing bytecode (i.e. compilation and

 internal tasks) at the end of the report. 

 A finer level than "info" will show individual compilation timings as they

 happen.

 Here is an example:

 [time] Accumulated complation phase Timings:

 [time] 

 [time] 'JavaScript Parsing'              1076 ms

 [time] 'Constant Folding'                 159 ms

 [time] 'Control Flow Lowering'            303 ms

 [time] 'Program Point Calculation'        282 ms

 [time] 'Builtin Replacement'               71 ms

 [time] 'Code Splitting'                   670 ms

 [time] 'Symbol Assignment'                474 ms

 [time] 'Scope Depth Computation'          249 ms

 [time] 'Optimistic Type Assignment'       186 ms

 [time] 'Local Variable Type Calculation'  526 ms

 [time] 'Bytecode Generation'             5177 ms

 [time] 'Class Installation'              1854 ms

 [time] 

 [time] Total runtime: 11994 ms (Non-runtime: 11027 ms [91%])

 * methodhandles

 If this logger is enabled, each MethodHandle related call that uses

 the java.lang.invoke package gets its MethodHandle intercepted and an

 instrumentation printout of arguments and return value appended to

 it. This shows exactly which method handles are executed and from

 where. (Also MethodTypes and SwitchPoints).

 * classcache

 This logger shows information about reusing code classes using the

 in-memory class cache. Nashorn will try to avoid compilation of

 scripts by using existing classes. This can significantly improve

 performance when repeatedly evaluating the same script.

 =======================

 3. Undocumented options

 =======================

 Here follows a short description of undocumented options for Nashorn.

 To see a list of all undocumented options, use the (undocumented) flag

 "-xhelp".

 i.e. jjs -xhelp or java -jar nashorn.jar -xhelp

 Undocumented options are not guaranteed to work, run correctly or be

 bug free. They are experimental and for internal or debugging use.

 They are also subject to change without notice.

 In practice, though, all options below not explicitly documented as

 EXPERIMENTAL can be relied upon, for example --dump-on-error is useful

 for any JavaScript/Nashorn developer, but there is no guarantee.

 A short summary follows:

 	-D (-Dname=value. Set a system property. This option can be repeated.)

 	-ccs, --class-cache-size (Size of the Class cache size per global scope.)

 	-cp, -classpath (-cp path. Specify where to find user class files.)

 	-co, --compile-only (Compile without running.)

 		param: [true|false]   default: false

 	-d, --dump-debug-dir (specify a destination directory to dump class files.)

 		param: <path>   

 	--debug-lines (Generate line number table in .class files.)

 		param: [true|false]   default: true

 	--debug-locals (Generate local variable table in .class files.)

 		param: [true|false]   default: false

 	-doe, -dump-on-error (Dump a stack trace on errors.)

 		param: [true|false]   default: false

 	--early-lvalue-error (invalid lvalue expressions should be reported as early errors.)

 		param: [true|false]   default: true

 	--empty-statements (Preserve empty statements in AST.)

 		param: [true|false]   default: false

 	-fv, -fullversion (Print full version info of Nashorn.)

 		param: [true|false]   default: false

 	--function-statement-error (Report an error when function declaration is used as a statement.)

 		param: [true|false]   default: false

 	--function-statement-warning (Warn when function declaration is used as a statement.)

 		param: [true|false]   default: false

 	-fx (Launch script as an fx application.)

 		param: [true|false]   default: false

 	--global-per-engine (Use single Global instance per script engine instance.)

 		param: [true|false]   default: false

 	-h, -help (Print help for command line flags.)

 		param: [true|false]   default: false

 	--loader-per-compile (Create a new class loader per compile.)

 		param: [true|false]   default: true

 	-l, --locale (Set Locale for script execution.)

 		param: <locale>   default: en-US

 	--log (Enable logging of a given level for a given number of sub systems. 

 	      [for example: --log=fields:finest,codegen:info].)

 		param: <module:level>,*   

 	-nj, --no-java (Disable Java support.)

 		param: [true|false]   default: false

 	-nse, --no-syntax-extensions (Disallow non-standard syntax extensions.)

 		param: [true|false]   default: false

 	-nta, --no-typed-arrays (Disable typed arrays support.)

 		param: [true|false]   default: false

 	--parse-only (Parse without compiling.)

 		param: [true|false]   default: false

 	--print-ast (Print abstract syntax tree.)

 		param: [true|false]   default: false

 	-pc, --print-code (Print generated bytecode. If a directory is specified, nothing will 

 	                  be dumped to stderr. Also, in that case, .dot files will be generated 

 	                  for all functions or for the function with the specified name only.)

 		param: [dir:<output-dir>,function:<name>]   

 	--print-lower-ast (Print lowered abstract syntax tree.)

 		param: [true|false]   default: false

 	-plp, --print-lower-parse (Print the parse tree after lowering.)

 		param: [true|false]   default: false

 	--print-mem-usage (Print memory usage of IR after each compile stage.)

 		param: [true|false]   default: false

 	--print-no-newline (Print function will not print new line char.)

 		param: [true|false]   default: false

 	-pp, --print-parse (Print the parse tree.)

 		param: [true|false]   default: false

 	--print-symbols (Print the symbol table.)

 		param: [true|false]   default: false

 	-pcs, --profile-callsites (Dump callsite profile data.)

 		param: [true|false]   default: false

 	-scripting (Enable scripting features.)

 		param: [true|false]   default: false

 	--stderr (Redirect stderr to a filename or to another tty, e.g. stdout.)

 		param: <output console>   

 	--stdout (Redirect stdout to a filename or to another tty, e.g. stderr.)

 		param: <output console>   

 	-strict (Run scripts in strict mode.)

 		param: [true|false]   default: false

 	-t, -timezone (Set timezone for script execution.)

 		param: <timezone>   default: Europe/Stockholm

 	-tcs, --trace-callsites (Enable callsite trace mode. Options are: miss [trace callsite misses] 

 	                         enterexit [trace callsite enter/exit], objects [print object properties].)

 		param: [=[option,]*]   

 	--verify-code (Verify byte code before running.)

 		param: [true|false]   default: false

 	-v, -version (Print version info of Nashorn.)

 		param: [true|false]   default: false

 	-xhelp (Print extended help for command line flags.)

 		param: [true|false]   default: false