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

The best trick is the generational garbage-collector. This keeps the heap unfragmented, so allocating memory is increasing the pointer to the free space and returning the old value. If memory runs out, the garbage-collection copy objects and creates this way a new unfragmented heap.

As different threads have to synchronize over the pointer to the free memory, if increasing it, they preallocate chunks. So a thread can allocate new memory, without the lock.

All of this is explained in more detail here: http://java.sun.com/javase/technologies/hotspot/gc/gc_tuning_6.html