Tuesday, June 01, 2010

Java Thread States

We had a little bit of debate last week about Java Thread states and I found the explanation for our questions in the Thread.State javadoc. The main question is the difference between BLOCKED and WAITING, but I guess this subtle difference is clear below:

NEW
Thread state for a thread which has not yet started.

RUNNABLE
Thread state for a runnable thread. A thread in the runnable state is executing in the Java virtual machine but it may be waiting for other resources from the operating system such as processor.

BLOCKED
Thread state for a thread blocked waiting for a monitor lock. A thread in the blocked state is waiting for a monitor lock to enter a synchronized block/method or reenter a synchronized block/method after calling Object.wait.

WAITING
Thread state for a waiting thread. A thread is in the waiting state due to calling one of the following methods:

* Object.wait with no timeout
* Thread.join with no timeout
* LockSupport.park

A thread in the waiting state is waiting for another thread to perform a particular action. For example, a thread that has called Object.wait() on an object is waiting for another thread to call Object.notify() or Object.notifyAll() on that object. A thread that has called Thread.join() is waiting for a specified thread to terminate.

TIMED_WAITING
Thread state for a waiting thread with a specified waiting time. A thread is in the timed waiting state due to calling one of the following methods with a specified positive waiting time:
* Thread.sleep
* Object.wait with timeout
* Thread.join with timeout
* LockSupport.parkNanos
* LockSupport.parkUntil

TERMINATED
Thread state for a terminated thread. The thread has completed execution.
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