Shulou(Shulou.com)06/01 Report--

This article introduces the knowledge of "what is the life cycle of Java threads". In the operation of actual cases, many people will encounter such a dilemma, so let the editor lead you to learn how to deal with these situations. I hope you can read it carefully and be able to achieve something!

The thread life cycle of Java has six states:

New (initialization status)

Runnable (runnable / operational status)

Blocked (blocking state)

Waiting (wait status without time limit)

Timed_Waiting (wait status with time limit)

Terminated (termination status)

1.New (initialization state): refers to a high-level language such as Java. The thread at the Java level has been created, but the thread in the operating system has not been created yet, so it is impossible to assign CPU to execute this thread at this time! So this state is unique to high-level languages, and operating system threads do not have this state. We New a thread, and it was in this state at that time.

2.Runnable (runnable / runnable state): CPU execution can be assigned in this state, which is where the thread is after we call the start () method in the New state.

3.Blocked (blocking state): CPU execution cannot be allocated in this state, and there is only one situation that will cause thread blocking, that is, synchronized! We know that synchronized-decorated methods or blocks of code can only be executed by one thread at a time, while other threads competing for locks go from Runnable to Blocked state! When a thread competes for a lock, it becomes Runnable.

Note that the Lock in the concurrent package leaves the thread waiting instead of blocking, and only synchronized is blocking. (it feels like a problem left over by history, there is no need for another blocking state and there is no difference between waiting)

4.Waiting (unlimited wait state): CPU cannot be allocated for execution in this state. There are three situations that bring the Runnable state to the waiting state

1. Call the Object.wait () method with no arguments. When notifyAll () or notify () wakes up, it will return to the Runnable state.

two。 Call the Thread.join () method with no arguments. That is, for example, if you set up a thread An in the main thread and call A.join (), then your main thread will not continue to execute until A has finished executing, this is your main thread is the waiting state.

3. Call the LockSupport.park () method. LockSupport is a utility class introduced by Java6. Locks in the Java concurrency package are all implemented based on it. If you call LocakSupport.unpark (Thread thread), you will return to the Runnable state.

5.Timed_Waiting (time-limited wait state): in fact, there is no difference in timeout between this state and Waiting, and CPU cannot be assigned to execute in this state. There are five situations that bring the Runnable state to the waiting state.

Object.wait (long timeout).

Thread.join (long millis).

Thread.sleep (long millis). Note that the internal call to Thread.sleep (long millis, int nanos) is actually Thread.sleep (long millis).

LockSupport.parkNanos (Object blocked,long deadline).

LockSupport.parkUntil (long deadline).

6.Terminated (termination status): after the normal run of our thread ends or half of the run is abnormal, that is the termination state!

Note that there is a method Thread.stop () that allows the thread to terminate, but this method has been discarded and is not recommended, because for example, if your thread gets a lock, the lock will disappear after you stop, and no other thread will be able to get the lock! It's over! So the interrupt () method is recommended.

Interrupt () causes threads in the state of Waiting and Timed_Waiting to throw interruptedException exceptions, so that threads in state of Runnabled will throw other exceptions if they operate in Iinterrupt O.

If the thread in the Runnabled state is not blocked in the Icano state, it can only actively detect whether it has been interrupted, using isInterrupted ().

This is the end of the content of "what is the life cycle of Java threads". Thank you for reading. If you want to know more about the industry, you can follow the website, the editor will output more high-quality practical articles for you!

Welcome to subscribe "Shulou Technology Information " to get latest news, interesting things and hot topics in the IT industry, and controls the hottest and latest Internet news, technology news and IT industry trends.