com.sun.squawk
Class Lisp2GenerationalCollector

java.lang.Object
  com.sun.squawk.GarbageCollector
      com.sun.squawk.Lisp2GenerationalCollector

public final class Lisp2GenerationalCollector
extends GarbageCollector

A collector based on the lisp 2 algorithm described in "Garbage Collection : Algorithms for Automatic Dynamic Memory Management" by Richard Jones, Rafael Lins.

Object Header Layout

For objects that move during a collection, forwarding offsets are installed in high bits of the class word in the object's header. The class pointer is made relative to the space in which the class lies (i.e. ROM, NVM or RAM) and this offset is stored in the lower bits. the two lowest bits of the class word are used as a determine if the object has forwarded ('00' if not) and if so, where is the class located ('01' in the heap, '11' in NVM and '10' in ROM). The forwarding offset is relative to the start of a "slice" with the absolute offset of the slice stored in a fixed size "slice offset table".

       <-------------- (W-C-2) ---------> <------ C ------> <-2->
      +----------------------------------+-----------------+-----+
      |  forwarding offset               | class offset    | tag |
      +----------------------------------+-----------------+-----+
       <--------------------------- w -------------------------->
                                          <-- sliceOffsetShift ->
 

Heap Layout

                      memoryEnd ->
                                    Slice table


                                    Bitmap


                                    Fixed marking stack

                        heapEnd ->                                                 --+
                                                                                     |
                                    Unused heap (except as extra marking stack)      |
                                                                                     |
              youngGenerationEnd ->                                                  |
                                                                                     |
                                    Young Generation                                 |
                                                                                     |
            youngGenerationStart ->                                                  | Covered by bitmap
                                                                                     |
                                    Old Generation                                   |
                                                                                     |
                       heapStart ->                                                  |
                                                                                     |
                                    {unused space to align heapStart for bitmap}     |
                                                                                     |
                     memoryStart ->                                                  |
                                                                                     |
                                    Permanent space                                  |
                                                                                     |
            permanentMemoryStart ->                                                --+
 

Field Summary

Fields inherited from class com.sun.squawk.GarbageCollector

NATIVE_GC_ONLY

Method Summary

int	getIdealYoungGenerationSize() Gets a size for the young generation based on its ideal ratio to the heap size.
int	getYoungGenerationSize() Gets the actual size (in bytes) of the young generation based on the current start address of the young generation, the ideal young generation size and the remaining amount of free memory in the heap.
void	setIdealYoungGenerationSizePercent(int ygPct) Sets the size for the young generation based on its ideal ratio to the heap size.

Methods inherited from class com.sun.squawk.GarbageCollector

getBytesAllocatedSinceLastGC, getBytesAllocatedTotal, getBytesFreedTotal, getBytesLastFreed, getBytesLastScanned, getLastGCTime, getMaxFullGCTime, getMaxGCTime, getMaxPartialGCTime, getTotalFullGCTime, getTotalGCTime, getTotalPartialGCTime

Methods inherited from class java.lang.Object

equals, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Method Detail

getIdealYoungGenerationSize

public int getIdealYoungGenerationSize()

Gets a size for the young generation based on its ideal ratio to the heap size.

Returns:

the ideal young generation size

getYoungGenerationSize

public int getYoungGenerationSize()

Gets the actual size (in bytes) of the young generation based on the current start address of the young generation, the ideal young generation size and the remaining amount of free memory in the heap.

Returns:

the minimum of the ideal young generation size and the amount of memory between the current start of the young generation and the end of the heap

setIdealYoungGenerationSizePercent

public void setIdealYoungGenerationSizePercent(int ygPct)

Sets the size for the young generation based on its ideal ratio to the heap size.

Parameters:

ygPct - the new young generation percent