Re: My (lack of )wisdom about threads

=?ISO-8859-1?Q?Arne_Vajh=F8j?= <>
Sun, 24 May 2009 14:47:40 -0400
Tom Anderson wrote:

On Sat, 23 May 2009, Joshua Cranmer wrote:

Stefan Ram wrote:

  So, inspired by ?Swing application architecture question.?, here is
  my (lack of )wisdoms about threads:

    - To correctly use multi-threading, a special education is needed.
      I do not yet have taken the time to undergo this, so I need
      to refrain from using threads (that is, more than one thread).

I wouldn't say that special education is needed at Java's level of
abstraction. I've been able to do it to some degree, and I certainly
never had it yet. If you know what synchronized does and when you
might want to use volatile, you'll probably be fine. Java 5 and 6 (and
possibly 7) introduce new concurrency utilities that eases some use,
especially if you have a lot of threads interacting.

Some of them also make life more complicated, because you have more

I do like AtomicBoolean, though. It lets you implement something that's
like an optional synchronized block. Rather than:

private final Object lock = new Object();

synchronized (lock) {

You do:

private final AtomicBoolean lock = new AtomicBoolean();

if (lock.compareAndSet(false, true)) {
    try {
    finally {

This still guarantees mutual exclusion, but means that if a second
thread comes along while a first thread is in the critical section,
rather than blocking, it skips over the critical section. I used this
construct to guard some housekeeping work in a multithreaded program;
something that needs to be done quite often, but must only be done by
one thread.

You could also use Semaphore.tryAcquire for a similar effect.

java.util.concurrent is a great package.

I assume that one could code the exact same thing oneself, but
it is always nice to get high quality code for free.


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