JVM: Runtime Data Area - PC Register (Program Counter)

JVM:Runtime Data Area

1. What is the pc register:
The pc register of the JVM is also called the program counter, which is an abstract virtual of the physical pc register.
It is used to store the address pointing to the next instruction, the instruction code to be executed, and the next instruction is read by the execution engine.

2.pc register features:
Each thread has a pc register, the pc register will store the jvm instruction address of the java method being executed by the current thread: if it is a local method, it is undefined (the local method refers to c orc++ code).
3. javap decompiles the id code, the left is the instruction address, the right is the instruction code, pc register stores the instruction address, the execution engine reads the stored instruction address in the pc registercorresponding command code.
4.Program branch, loop, jump, exception handling, thread recovery, depend on pc register.
When the bytecode interpreter works, it iterates by changing the value of this counter and reads the next bytecode instruction to be executed.
He is the only area that does not have an oom case in the java virtual machine specification.

Method area, heap have gc
Stack and pc registers have no gc

Two questions about the pc register: (eight-legged text)
What is the use of the pc register to store the bytecode instruction address?
The cpu needs to constantly switch threads. After the thread switches back, where to continue execution, it needs the pc register to tell it.

Why use the pc register to record the execution address of the current thread?
The bytecode interpreter needs to change the value of the pc register to know what bytecode instruction should be executed next.