JVM

class loader

load code class and other java base classes such as java.io util …
class loader

  • static class will be loaded in prepare in link
  • Resolve change symbol reference to actural address

  • parallel to speed up

  • NoClassDeFoundError from the first load part

  • ClassNotFoundException from solve in link

runtime data: memory

runtime

  • metaspace: class like static, default 64MB max before Java 8
  • heap: 25% space of memory
    pay attention: heap is not the HEAP in data structure. It’s just an area in memory to store all objects.
  • pc register: record each threads’s pc
    which is a fixed concept representing an address in system

  • stack frame stores local data and addresses of objects
    actually, t1 points address of metaspace because the code is complied as byte code

  • Qustions:

    • OutOfMemoryError: PermGen Space
      1 PermGen Space is another name of metaspace
    • StackOverFlowError: 4 and 5

Execution Engine

execution

  • JIT(just in time) Compiler: like cache to store those functions would be used frequently
  • Hotspot profiler will count the calls of each func. When the number exceed the threshold
    each time the count exceed some number, give a faster complier and reset to zero, count again
  • Garbage collection will save space by eliminating unuseful object

summary

whole

reference

https://www.youtube.com/watch?v=ZBJ0u9MaKtM
https://www.youtube.com/watch?v=UnaNQgzw4zY
https://www.youtube.com/watch?v=_8-ht2AKyH4