07 local method stack

1. Introduce

• Java The virtual machine stack is used to manage Java Method call , The local method stack is used to manage calls to local methods .
• Native Method Stack , It's also thread private .
• The memory can be dynamically expanded （ In terms of memory overflow, it is the same as the virtual machine stack ）
  • If the stack capacity allocated by thread request exceeds the maximum allowed capacity of local method stack ,Java The virtual machine will throw a StackoverflowError abnormal .
  • If the native method stack can be dynamically extended , And can't get enough memory when trying to expand , Or when creating a new thread, there is not enough memory to create the corresponding local method stack , that Java The virtual machine will throw a OutofMemoryError abnormal .
• Local methods generally use C The realization of language .
• Its concrete method is Native Method Stack Registered in native Method , stay Execution Engine Load local method library on execution .
  

2. Other matters

• When a thread calls a local method , It's entering a whole new world that's no longer limited by virtual machines . It has the same permissions as a virtual machine .
  • Local methods can be implemented through local method interfaces Access the runtime data area inside the virtual machine
  • It can even use the registers in the local processor directly
  • Allocate any amount of memory directly from the local memory heap
• Not all JVM Both support local methods . because Java The virtual machine specification does not explicitly require the language of the local method stack 、 How to realize it 、 Data structure, etc . If JVM The product is not intended to support native Method , You don't need to implement a local method stack .
• stay Hotspot JVM in , Directly combines the local method stack with the virtual machine stack .