Parallelism, concurrency and life cycle of threads

This article is only a simple record , For more professional content, it is recommended to read about threads in the operating system 、 Knowledge of processes .

Concurrency and parallelism

Running programs （ Software ） It's an independent process , Threads belong to processes , Multiple threads are actually concurrent and parallel .

Understanding of concurrency
1.CPU The number of simultaneous processing threads is limited ;
2.CPU Will poll for each thread of the system , because CPU The switching speed is very fast , It gives us the feeling that these threads are executing at the same time , This is concurrency .

Parallel understanding
At the same time , There are multiple threads being used at the same time CPU Process and execute .

Declaration cycle of thread

State of thread
That is, the process of thread from birth to death , And various states and state transitions in the middle , Understanding the state of threads is helpful to improve the understanding ability of concurrent programming .

Java State of thread
Java In all, it defines 6 States , It's defined in Thread The internal enumeration of the class .

     public enum State {
    
         	NEW,
         	RUNNABLE,
         	BLOCKED,
         	WAITING,
         	TIMED_WAITING,
         	TERMINATED;
}

state	explain
NEW( newly build )	Thread just created , But it didn't start
Runnable( Can run )	The thread has called start() wait for CPU Dispatch
Blocked( The lock is blocked )	The thread does not compete for the lock object when executing , Then the thread enters Blocked state
Waiting( Wait indefinitely )	A thread enters Waiting state , Another thread called notify perhaps notifyAll Method to wake up
Timed Waiting( Time wait for )	Same as waiting state , There are several methods that have timeout parameters , Call them and they will enter Timed Waiting state . Common methods with timeout parameters are Thread.sleep 、Object.wait
Teminated( Terminated )

Knowledge Links ：Java Thread communication

Thread 6 Mutual transformation of States