Gc info

Column "Number created"

This is the number of objects (of the specified type) created since program start, (i.e. this figure is accumulative). This is not the number of actually existing objects.

Column "Total size"

This is the same as "Number created", except the unit is bytes.

Column "Store left"

This is the number of free objects left in the "store chunk" of the specified type. This number is mainly interesting because it is zero for the type that triggered the collection cycle. Here's why: the gc will firstly allocate new objects in the store chunk. Only when there is no store left will the gc start looking for space elsewhere, which will result in one of the following outcomes:

• Previously reclaimed garbage is recycled as a new object.
• A new store chunk is allocated.
• A garbage collection cycle is started. If garbage of the correct type was reclaimed, garbage is recycled. Else, a new store chunk is allocated.

Where is the information about the freed memory, i.e. about the effect of the last GC cycle?

I am sad to report that this information is currently missing.

What does the cryptic final lines mean?

C-stack=xx

xx is the number of pointers in the stack, i.e. the number of conservative roots.

main-table=xx/yyyy

xx is the number of memory chunks currently allocated. yyyy is the number of chunks that the main table can hold. When xx grows larger than yyyy, the gc needs to realloc a larger main table (not a very costly operation unless yyyy is huge).

fsoc:xx(free=yy ceil=zz)

xx is the number of memory chunks currently allocated to fixed-size objects (all objects except NATIVE_ARRAYs). yy is the number of free memory chunks, that is chunks that are devoted to fixed-size objects, but that do not hold any objects. zz is the number of chunks that can be allocated to fixed-size objects before a gc-cycle is triggered.

When the gc needs to allocate a new object and it has exhausted that type's store chunk and reclaimed garbage, it tries to find a new store chunk for that type. If yy is non-null, a free memory chunk is converted to a store chunk. Else, if xx is smaller than zz, a chunk is allocated from the system. Else, a garbage-collection cycle is started.

rsoc:xx(ceil=yy)

xx is the number of memory chunks currently allocated to resizable objects (NATIVE_ARRAYs). yy is the number of chunks that can be allocated to resizable objects before a gc-cycle is triggered.