IBM User Guide for Java V7 on Windows > Troubleshooting and support > Using diagnostic tools > Using Heapdump > Portable Heap Dump (PHD) file format

PHD array records

PHD array records can cover primitive arrays and object arrays.

Primitive array record

The primitive array record contains:

• The 1 byte tag. The third bit (0x20) is set and the following 5 bits in descending order contain:
  • 3 bits containing the array type. The array type values are:
    • 0 = bool
    • 1 = char
    • 2 = float
    • 3 = double
    • 4 = byte
    • 5 = short
    • 6 = int
    • 7 = long

  • 2 bits indicating the length of the array size and also the length of the gap. These values apply:
    • 0 indicates a "byte".
    • 1 indicates a "short".
    • 2 indicates an "int".
    • 3 indicates a "long".

• "byte", "short", "int" or "long" containing the gap between the address of this object and the address of the preceding object. For more information, see the description in the short object record format.
• "byte", "short", "int" or "long" containing the array length.
• If all objects are hashed, a "short" containing the hashcode.

Long primitive array record

The long primitive array record is used when a primitive array has been hashed. The format is:

• The 1 byte tag containing the value 7.
• A "byte" containing flags, with these bits in descending order:
  • 3 bits containing the array type. For more information, see the description of the primitive array record.
  • 1 bit indicating the length of the array size and also the length of the gap. The range for this value includes:
    • 0 indicating a "byte".
    • 1 indicating a "word".

  • 2 unused bits.
  • 1 bit indicating if the object was hashed and moved. If this bit is set, the record includes the hashcode.
  • 1 bit indicating if the object was hashed.

• a "byte" or "word" containing the gap between the address of this object and the address of the preceding object. For more information, see the description in the short object record format.
• a "byte" or "word" containing the array length.
• If all objects are hashed, a "short" containing the hashcode. Otherwise, an optional "int" containing the hashcode if the hashed and moved bit is set in the record flag byte.

Object array record

The object array record format is:

• The 1 byte tag containing the value 5.
• A "byte" containing flags with these bits in descending order:
  • 2 bits to indicate whether the gap is "byte", "short", "int" or "long".
  • 2 bits indicating the size of each reference. For more information, see the description in the short record format.
  • 2 unused bits.
  • 1 bit indicating if the object was hashed and moved. If this bit is set, the record includes the hashcode.
  • 1 bit indicating if the object was hashed.

• A "byte", "short", "int" or "long" containing the gap between the address of this object and the address of the preceding object. For more information, see the description in the short record format.
• A "word" containing the address of the class of the objects in the array. Object array records do not update the class cache.
• If all objects are hashed, a "short" containing the hashcode. If the hashed and moved bit is set in the records flag, this field contains an "int".
• An "int" containing the length of the array of references.
• The array of references. For more information, see the description in the short record format.

Object array record (revised) - from PHD version 5

This array record is similar to the previous array record with two key differences:

1. The tag value is 8.
2. An extra "int" value is shown at the end. This int contains the true array length, shown as a number of array elements. The true array length might differ from the length of the array of references because null references are excluded.

This record type was added in PHD version 5.

Parent: Portable Heap Dump (PHD) file format

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