-XX:[+|-]HitachiLocalsInThrowable (Option for collecting the local variable information when an exception occurs)

Format

-XX:+HitachiLocalsInThrowable

This option outputs the local variable information of the methods in the stack trace.

The -XX:+HitachiLocalsInThrowable option is ignored when java.lang.StackOverflowError occurs.

-XX:-HitachiLocalsInThrowable

This option does not output the local variable information of the methods in the stack trace.

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Description

When the java.lang.Throwable.fillInStackTrace method is executed, the local variable information of the method in the stack trace is collected.

Default value

• -XX:-HitachiLocalsInThrowable

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Output format

  locals:
   name: <name>
   type: <type>
   value: <value>
...

The output contents are explained below:

• In the first line, "locals:" header is output.

• From second line onwards, the following information is output line by line for each local variable that can be collected:

  1. Variable name

  2. Type name (basic type name, class name, or array type name)

  3. Character string that represents variable value

Note that the output contents of each local variable are demarcated with a blank line.

name

Local variable name.

For the argument passed to the method, [arg***](*** is the argument number) will be displayed in continuation to the variable name.

type

Type name of the local variable (the basic type name, class name, or the array type name)

value

Character string representing the value of local variable

• Basic type:

  Value converted as it is into a character string

• Class or array type:

  When variable type is null: (null)

  Other than the above-mentioned: existing-address-of-the-object

Maximum length of the character string representing a value is 64. When the character string exceeds the maximum length, the characters up to 64th character are output and after that "..." character string is output. In the case of the class or array type, you can add detailed expressions by specifying the following add options:

• -XX:+HitachiLocalsSimpleFormat

• -XX:+HitachiTrueTypeInLocals

• -XX:HitachiCallToString

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Examples of output

The following is an example of output using Java program example 1:

When all the local variable information is output

 at Example1.method(Example1.java:15)
  locals:
   name: this
   type: Example1
   value: <0x922f42d0>
 
   name: l1 [arg1]
   type: int
   value: 1
 
   name: l2 [arg2]
   type; char
   value: 'Q'
 
   name: l3 [arg3]
   type: java.lang.Object
   value: <0xaf112f08>
 
   name: l4
   type: float
   value: 4.000000
 
   name: l5
   type: boolean
   value: true
 
   name: l6
   type: double
   value: 1.79769E+308
 
   name: l7
   type: java.lang.Object[]
   value: <0x922f42d8>
 
 at Example1.main(Example1.java:5)
  locals:
...

When the local variable information does not exist

• For a class file generated without adding the -g option or the -g:vars option

• For the native method of a class file generated by adding the -g option or the -g:vars option

   at Example1.method(Example1.java:15)
    locals:
     name: this
     type: Example1
     value: <0x922f42d0>
   
     name: [arg1]
     type: int
     value: 1
   
     name: [arg2]
     type; char
     value: 'Q'
   
     name: [arg3]
     type: java.lang.Object
     value: <0xaf112f08>
   
   at Example1.main(Example1.java:5)
    locals:
  ...

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Precautions

• To collect complete local variable information, while you are creating the class file in javac, you need to add the -g option or the -g:vars option and fill the local variable information in the class file. For the class file created without adding the -g option or the -g:vars option, the local variable information is output in the collectable range.

• The local variable information does not exist for the native method even if the class file is generated by adding the -g option or the -g:vars option.

• When the JIT compiler compiles a method, as a part of optimization, the local variables determined as unnecessary, are removed.

  (Example) Consider a declaration and local variable that is not used after initialization as "int not_used = 12345":

  In this case, the following value is output in the local variable information when an exception occurs:

  Type name	Output information
  boolean type	false
  char type	'\0'
  byte type Short type int type long type float type double type	0
  class type array type	(null)

• When the local variable information of the method containing complicated control structure and multiple lines is to be output, analysis takes time, and hence, when an exception occurs the process for generating the exception object may take longer time.

• To output the local variable information to the stack trace of the current thread obtained by using the getStackTrace method of the java.lang.Thread class, you must set up the option for collecting the local variable information for an exception (-XX:+HitachiLocalsInThrowable), which outputs the local variable information to the stack trace used for an exception.

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