This question was asked two years ago, but the resources it mentions are either not very helpful (IMHO) or links are no longer valid.
There must be some good tutorials out there to understand Phaser. I've read the javadoc, but my eyes glaze over, since in order to really understand the javadoc you kind of have to know how these classes are supposed to be used.
Anyone have any suggestions?
For Phaser at least, I think the JavaDoc offers a fairly clear explanation. This is a class that you would use to synchronize a batch of threads, in the sense that your can register each thread in the batch with a Phaser and then use the Phaser to have them block until every thread in the batch has notified the Phaser, at which point any blocked thread(s) will begin executing. This wait/notify cycle can repeat over and over again, as desired/required.
Their sample code gives a reasonable example (though I very much dislike their 2-character indentation style):
void runTasks(List<Runnable> tasks) {
final Phaser phaser = new Phaser(1); // "1" to register self
// create and start threads
for (final Runnable task : tasks) {
phaser.register();
new Thread() {
public void run() {
phaser.arriveAndAwaitAdvance(); // await all creation
task.run();
}
}.start();
}
// allow threads to start and deregister self
phaser.arriveAndDeregister();
}
This sets up a Phaser with a registration count of tasks.size() + 1, and for each task creates a new Thread which will block until the next advance of the Phaser (i.e. the time at which tasks.size() + 1 arrivals have been recorded) and then run its associated task. Each Thread that is created is also instantly started, so the Phaser comes out of the loop with tasks.size() arrivals recorded.
The final call to phaser.arriveAndDeregister() will record the final arrival, and also decrement the registration count so that it now equals tasks.size(). This causes the Phaser to advance, which in effect allows all the tasks to start running at the same time. This could be repeated by doing something like:
void