Obtaining A Thread’s State

Obtaining A Thread’s State

As mentioned earlier in this chapter, a thread can exist in a number of different states. You can obtain the current state of a thread by calling the getState( ) method defined by Thread. It is shown here:

Thread.State getState( )

It returns a value of type Thread.State that indicates the state of the thread at the time at which the call was made. State is an enumeration defined by Thread. (An enumeration is a list of named constants. It is discussed in detail in Chapter 12.) Here are the values that can be returned by getState( ):

Given a Thread instance, you can use getState( ) to obtain the state of a thread. For example, the following sequence determines if a thread called thrd is in the RUNNABLE state at the time getState( ) is called:

Thread.State ts = thrd.getState();

if(ts == Thread.State.RUNNABLE) // ...

It is important to understand that a thread’s state may change after the call to getState( ). Thus, depending on the circumstances, the state obtained by calling getState( ) may not reflect the actual state of the thread only a moment later. For this (and other) reasons, getState( ) is not intended to provide a means of synchronizing threads. It’s primarily used for debugging or for profiling a thread’s run-time characteristics.