Java nonblocking memory allocation

Question

I read somewhere that java can allocate memory for objects in about 12 machine instructions. It\'s quite impressive for me. As far as I understand one of tricks JVM using is pre

Answer 1

There is no single memory allocator for the JVM. IIRC Sun's JVM and IBM's managed memory differently. However generally the way the JVM will operate is that it will initially allocate one piece of memory, this segment will be small enough to live in the processors cache making all access to this extremely fast.

As the application creates objects, the objects will take memory from within this segment. The object allocation within the segment is simply pointer arithmetic.

Initially the offset address into the freshly minted segment will be zero. The first object allocated will have an 'address' (actually an offset into the segment) of zero. When you allocate object then the memory manager will know how big the object is, allocate that much space within the segment (16 bytes say) and then increment it's "offset address" by that amount meaning that memory allocation is blindingly fast, it's just pointer arithmetic.

Sun have a whitepaper here Memory Management in the JavaHotSpot™ Virtual Machine and IBM used to have a bunch of stuff on ibm.com/developerworks