I want to understand how java allocates objects in heap. I want to know which parts of the JDK code are triggered when the “new” keyword is used. How can I define a function that a user can call from the java code and that would implement functionality in JDK source code? I am aware of the fact that jdk14 uses G1GC as a default garbage collector and G1GC code is present in jdk14/src/hotspot/share/GC/G1 folder but I am unable to follow G1Allocator allocates memory to the user threads(if it does).
Advertisement
Answer
Any known implementation will use TLAB (thread local allocation buffer) by default when allocating memory. Without it – the allocation would be much more slower. Though I have not dived into the code too much about this subject, you can start from here, for example.
There is a very good comment in the source code about what happens when a new is requested here. Basically if TLAB can be used (an Object is not bigger than that for example), it will be; otherwise raw malloc for every new will be done.
Regarding G1 here are the mains points of what it does. A general explanation is again in the comments, with a phrase :
All non-TLAB allocation requests should go to mem_allocate()
What mem_allocate does can be started from here.