What does the java thread's state really mean?

Question

I am learning the tool in Android Studio, get thread dump, as follow:

I notice the different state of every thread like this,

I can see there are runnable,sleeping,waiting. And I deep into the thread stack, most thread stack like this,

"<61> RxComputationScheduler-3@830064517520" daemon prio=5 waiting
    java.lang.Thread.State: WAITING
        at java.lang.Object.wait(Object.java:-1)
        at java.lang.Thread.parkFor(Thread.java:1205)
        at sun.misc.Unsafe.park(Unsafe.java:325)
        at java.util.concurrent.locks.LockSupport.park(LockSupport.java:157)
        at java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.await(AbstractQueuedSynchronizer.java:2017)
        at java.util.concurrent.ScheduledThreadPoolExecutor$DelayedWorkQueue.take(ScheduledThreadPoolExecutor.java:1050)
        at java.util.concurrent.ScheduledThreadPoolExecutor$DelayedWorkQueue.take(ScheduledThreadPoolExecutor.java:778)
        at java.util.concurrent.ThreadPoolExecutor.getTask(ThreadPoolExecutor.java:1035)
        at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1097)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:587)
        at java.lang.Thread.run(Thread.java:841)

I am confused that they do all halt at Object.wait, however the state of thread can be runnable,sleeping,waiting?

Here is the other state thread's stack.

RUNNABLE

<53> RxSchedulerPurge-1@830057651944" daemon prio=5 runnable
  java.lang.Thread.State: RUNNABLE
      at java.lang.Object.wait(Object.java:-1)
      at java.lang.Thread.parkFor(Thread.java:1205)
      at sun.misc.Unsafe.park(Unsafe.java:325)
      at java.util.concurrent.locks.LockSupport.parkNanos(LockSupport.java:197)
      at java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.awaitNanos(AbstractQueuedSynchronizer.java:2056)
      at java.util.concurrent.ScheduledThreadPoolExecutor$DelayedWorkQueue.take(ScheduledThreadPoolExecutor.java:1062)
      at java.util.concurrent.ScheduledThreadPoolExecutor$DelayedWorkQueue.take(ScheduledThreadPoolExecutor.java:778)
      at java.util.concurrent.ThreadPoolExecutor.getTask(ThreadPoolExecutor.java:1035)
      at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1097)
      at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:587)
      at java.lang.Thread.run(Thread.java:841)</code>

TIMED_WAITING

<58> RxScheduledExecutorPool-2@830064740632" daemon prio=5 sleeping
  java.lang.Thread.State: TIMED_WAITING
      at java.lang.Object.wait(Object.java:-1)
      at java.lang.Thread.parkFor(Thread.java:1205)
      at sun.misc.Unsafe.park(Unsafe.java:325)
      at java.util.concurrent.locks.LockSupport.parkNanos(LockSupport.java:197)
      at java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.awaitNanos(AbstractQueuedSynchronizer.java:2056)
      at java.util.concurrent.ScheduledThreadPoolExecutor$DelayedWorkQueue.take(ScheduledThreadPoolExecutor.java:1062)
      at java.util.concurrent.ScheduledThreadPoolExecutor$DelayedWorkQueue.take(ScheduledThreadPoolExecutor.java:778)
      at java.util.concurrent.ThreadPoolExecutor.getTask(ThreadPoolExecutor.java:1035)
      at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1097)
      at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:587)
      at java.lang.Thread.run(Thread.java:841)

Cordless

Please use code instead of images for the stack trace. – Opera

Please start accepting answers. I'm not talking about this question in particular, I'm talking about all your questions where you have good but unaccepted answers. – Empson

Answer 1

New means the thread is in new state if you create an instance of Thread class but before the invocation of start() method:

Thread t = new Thread(...); // t is New

Runnable means the thread is in runnable state after invocation of start() method. Basically:

t.start(); // t is Runnable

Running is the "sub-state" of Runnable: the thread is in running state if the thread scheduler has selected it. You can't do anything with it explicitly, meaning you call start() and then just wait.

Ready is another "sub-state" of Runnable: the thread is eligible for running and waits for the thread scheduler to select it.

Blocked means the state when the thread is still alive, but is currently not eligible to run. This happens, for example, when one thread comes across a synchronized block, which is processed by another thread. In this case the first thread becomes blocked.

Waiting is the state when your thread is neither blocked nor ready. This usually happens when you call wait() or join() on a thread.

Thread t1 = new Thread(); // t1 is New
Thread t2 = new Thread(); // t2 is New
t1.start(); // t1 becomes Runnable
t2.start(); // t2 becomes Runnable
t1.join(); // t2 becomes Waiting, because t1 is processed until it terminates

There is also a state called Timed Waiting, which is almost the same thing, but is caused by calling sleep(). If you call wait(timeout) or join(timeout), the thread also gets timed waiting state.

Thread t = new Thread(); // t is New
t.start(); // t is Runnable
t.sleep(4000); // t get state of Timed Waiting for 4 seconds

Terminated is a thread in terminated or dead state when it's run() method exits.

I think I covered it all :) Here is an image to help you understand it more clearly:

As JoxTraex requested, here're sources I read before posting:

1. https://docs.oracle.com/javase/7/docs/api/java/lang/Thread.State.html
2. javarush.ru
3. http://www.uml-diagrams.org/examples/java-6-thread-state-machine-diagram-example.html
4. http://www.journaldev.com/1044/thread-life-cycle-in-java-thread-states-in-java

It's just a matter of good googling skill, really...

Empson

Could you please post your source and where you ate getting this info from? – Unfortunate

Answer 2

public static enum Thread.State
extends Enum<Thread.State>

A thread state. A thread can be in one of the following states:

NEW
A thread that has not yet started is in this state.

RUNNABLE
A thread executing in the Java virtual machine is in this state.

BLOCKED
A thread that is blocked waiting for a monitor lock is in this state.

WAITING
A thread that is waiting indefinitely for another thread to perform a particular action is in this state.

TIMED_WAITING
A thread that is waiting for another thread to perform an action for up to a specified waiting time is in this state.

TERMINATED
A thread that has exited is in this state.

A thread can be in only one state at a given point in time. These states are virtual machine states which do not reflect any operating system thread states.

refer oracle's api for more information.

Subsidence