[THRIFT-1469] Java isset space optimization

• Type: Improvement
• Status: Closed
• Priority: Minor
• Resolution: Fixed
• Affects Version/s: 0.8
• Fix Version/s: 0.9
• Component/s: Java - Compiler
• Labels: patch
• Patch Info: Patch Available
• Assignee: Brian Bloniarz
• Reporter: Brian Bloniarz
• Created: 19/Dec/11 20:41
• Updated: 21/Dec/11 19:58
• Resolved: 21/Dec/11 18:15

Description

Attached is a small patch and unit tests for Java to optimize the heapspace
footprint of (for example):

struct OptIntPair {
1: i32 a
2: i32 b
}

Each instance will have an __isset_bit_vector which points to a BitSet,
which points to a long[], adding around 50 bytes of overhead to this object.

The patch changes this by storing a raw byte and doing direct bitfield operations, like:
byte __isset_bitfield;

public void unsetB()

{ __isset_bitfield = EncodingUtils.clearBit(__isset_bitfield, __B_ISSET_ID); }

A little nasty, but a big space win: on my machine, this brings down the total
size of an OptIntPair from 85 bytes to 25 bytes. A BitSet gets used as a fallback
when more than 64 __isset entries are needed.