THE PACKAGE JAVA.LANG

java.lang.Thread

20.20

Some thread invokes the

exit

 method ( 20.16.2) of class

Runtime

 (and the

security manager ( 20.17.13) approves execution of the

exit

 operation); this

stops every thread being run by the Java Virtual Machine that is running the

thread that invokes the

exit

 method.

As a thread dies, the

notifyAll

 method ( 20.1.10) is invoked for the

Thread

object that represents it; this fact is important for the proper operation of the

join

methods ( 20.20.28,  20.20.29,  20.20.30). A thread is also removed from its

thread group as it dies. Once a thread has been stopped, it is no longer alive and it

cannot be restarted.

A thread that is alive can be

suspended

 and

resumed

. A suspended thread is

considered to be alive, but it performs no work, makes no progress, executes no

virtual machine instructions. Resumption restores a thread to the state of active

execution. A thread is suspended when it or another thread calls the

suspend

method ( 20.20.17) of the

Thread

 object that represents it (and the security man 

ager ( 20.17.11) approves execution of the

suspend

 operation). A thread is

resumed when another thread calls the

resume

 method ( 20.20.18) of the

Thread

object that represents it (and the security manager ( 20.17.11) approves execution

of the

resume

 operation).

Every thread has a

priority

. When there is competition for processing

resources, threads with higher priority are generally executed in preference to

threads with lower priority. Such preference is not, however, a guarantee that the

highest priority thread will always be running, and thread priorities cannot be used

to implement mutual exclusion. When code running in some thread creates a new

Thread

 object, the newly created thread has its priority initially set equal to the

priority of the creating thread. But the priority of a thread

T

 may be changed at

any time if some thread invokes the

setPriority

 method of the

Thread

 object

that represents

T

 (and the security manager ( 20.17.11) approves execution of the

setPriority

 operation).

Each thread may or may not be marked as a

daemon

. When code running in

some thread creates a new

Thread

 object, the newly created thread is a daemon

thread if and only if the creating thread is a daemon. But the daemonhood of a

thread

T

 may be changed before it is activated if some other thread invokes the

setDaemon

 method of the

Thread

 object that represents

T

 (and the security man 

ager ( 20.17.11) approves execution of the

setDaemon

 operation).

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