One 、 basic

• The red part ： Will be created as the virtual machine starts , Destroy with virtual machine exit
• The gray part ： One to one correspondence with thread , As the thread starts and ends , And end with it
• One Runtime, Corresponding to one JVM virtual machine
  
  

Two 、 Concept

1. Threads

1.  A thread is a running unit in a program , JVM Allow an application to have multiple threads executing in parallel 
2.  Each thread is mapped directly to the local thread of the operating system 
    2.1  When one java When the thread is ready , At this point, a local thread of the operating system will also be created 
    2.2 java After thread execution is terminated , Local threads also recycle 
3.  The operating system is responsible for scheduling threads to any available cpu On 
    Once the local thread is initialized successfully , Will call java In thread run()

2. Program counter

2.1 Concept

• PC register , PC Register, Program Counter Register, Instruction counter
• Thread code instructions ： Save and retrieve again through the program counter , Is used for thread switching
• A thread will contain a program counter , Record the number of lines executed by code instructions , It belongs to thread private
• The storage space is small , Almost negligible , It is also the fastest
• non-existent OOM

 At any time, a thread has only one method to execute ( The current method )
 Store what the current thread is executing java Methodical jvm Instruction address , If you execute native Method , It is undefined