Threads can be in one of six states:
Each of these states is explained in the sections that follow. To determine the current state of a thread, simply call the getState method.
When you create a thread with the new operator—for example, new Thread(r)—the thread is not yet running. This means that it is in the new state. When a thread is in the new state, the program has not started executing code inside of it. A certain amount of book keeping needs to be done before a thread can run.
Once you invoke the start method, the thread is in the runnable state. A runnable thread may or may not actually be running. It is up to the operating system to give the thread time to run. (The Java specification does not call this a separate state, though. A running thread is still in the runnable state.)
Once a thread is running, it doesn’t necessarily keep running. In fact, it is desirable if running threads occasionally pause so that other threads have a chance to run. The details of thread scheduling depend on the services that the operating system provides. Preemptive scheduling systems give each runnable thread a slice of time to perform its task. When that slice of time is exhausted, the operating system preemptsthe thread and gives another thread an opportunity to work (see Figure below). When selecting the next thread, the operating system takes into account the thread priorities.
All modern desktop and server operating systems use preemptive scheduling. However, small devices such as cell phones may use cooperative scheduling. In such adevice, a thread loses control only when it calls the yield method, or it is blocked or waiting.
On a machine with multiple processors, each processor can run a thread, and you can have multiple threads run in parallel. Of course, if there are more threads than processors, the scheduler still has to do time-slicing. Always keep in mind that a runnable thread may or may not be running at any given time.(This is why the state is called “runnable” and not “running.”).
Blocked and Waiting Threads
When a thread is blocked or waiting, it is temporarily inactive. It doesn’t execute any code and it consumes minimal resources. It is up to the thread scheduler to reactivate it.
The details depend on how the inactive state was reached.
the states that a thread can have and the possible transitions from one state to another. When a thread is blocked or waiting (or, of course, when it terminates), another thread will be scheduled to run. When a thread is reactivated (for example, because its timeout has expired or it has succeeded in acquiring a lock), the scheduler checks to see if it has a higher priority than the currently running threads. If so, it preempts one of the current threads and picks a new thread to run.
A thread is terminated for one of two reasons:
In particular, you can kill a thread by invoking its stop method. That method throws a ThreadDeath error object that kills the thread. However, the stop method is deprecated, and you should never call it in your own code.
This method is deprecated.
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Core Java Tutorial
An Introduction To Java
The Java Programming Environment
Fundamental Programming Structures In Java
Objects And Classes
Interfaces And Inner Classes
User Interface Components With Swing
Deploying Applications And Applets
Exceptions, Logging, Assertions, And Debugging
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