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Java 101: Understanding Java threads, Part 4: Thread groups, volatility, and thread-local variables

Final concepts for improving Java application programming with Java threads

By Jeff Friesen, JavaWorld.com, 08/02/02

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Page 8 of 8

About to do something.
My Thread unable to do something. Reason: Second reason.
Cleaning up

Caution: ThreadDeath is a powerful tool for causing a thread to terminate its execution. However, this tool is dangerous, and is the reason Sun deprecated the stop() method. When a thread throws a ThreadDeath object, all locked monitors unlock as ThreadDeath propagates up the method-call stack. Objects protected by these monitors become accessible to other threads. If those objects are in an inconsistent state, a program can experience erratic behavior, a database or file can corrupt, and so on. However, if you know that the thread is not holding any locks, you can safely throw ThreadDeath.

Review

This article completes my coverage of threads by exploring thread groups, volatility, thread-local variables, timers, and ThreadDeath. You learned to use thread groups to group related threads, to use volatility to allow threads access to main-memory copies of shared field variables, to use thread-local variables to give threads their own independently initialized values, to use timers to schedule the execution of tasks either periodically or for a one-time execution, and to use ThreadDeath to let a thread prematurely exit from its run() method.

Next month I'll show you how to use packages to organize your classes and interfaces.

About the author

Jeff Friesen has been involved with computers for the past 20 years. He holds a degree in computer science and has worked with many computer languages. Jeff has also taught introductory Java programming at the college level. In addition to writing for JavaWorld, he has written his own Java book for beginners? Java 2 by Example, Second Edition (Que Publishing, 2001; ISBN: 0789725932)?and helped write Using Java 2 Platform, Special Edition (Que Publishing, 2001; ISBN: 0789724685). Jeff goes by the nickname Java Jeff (or JavaJeff). To see what he's working on, check out his Website at http://www.javajeff.com.

Read more about Core Java in JavaWorld's Core Java section.

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Resources
  • Learn more about Java: See the complete listing for Jeff Friesen's Java 101 series -- archived on JavaWorld.
  • Also see the Java Tips series: More than five years of compiled tips from JavaWorld's expert readers.