Java's Phaser class is a multi-threaded synchronization aid that supports a form of cooperative task scheduling. In other words, Phaser can be used to schedule and coordinate the execution of a set of tasks across multiple threads.
Phaser is particularly well-suited for use in concurrent, multi-team development environments. For example, imagine that you are working on a large project with a team of developers. Each developer is working on a different task, and each task has a different timeline. In order to coordinate the work of all the developers, you can use Phaser to schedule the tasks.
Phaser is most commonly used in situations where multiple threads need to cooperatively work on a task. For example, Phaser can be used to schedule the tasks of a multi-threaded development team.
Phaser can also be used to schedule tasks that are not necessarily related to development. For example, Phaser can be used to schedule the execution of a set of tasks across multiple cores of a CPU.
When you use Phaser, you need to first create a Phaser instance. You can then use the Phaser instance to schedule the tasks.
Creating a Phaser instance is straightforward. You simply need to specify the number of threads that will be using the Phaser instance. For example, if you are using Phaser to schedule the tasks of a four-threaded development team, you would specify 4 as the number of threads:
Phaser phaser = new Phaser(4);
Once you have created a Phaser instance, you can use it to schedule the tasks. To do this, you simply need to call the register()
method of the Phaser instance. For example, to schedule the task of thread 1, you would call the register()
method as follows:
phaser.register();
After calling the register()
method, the thread will be added to the Phaser instance and will be able to participate in the Phaser's scheduling.
Once the threads have been registered with the Phaser instance, you can use the Phaser's arriveAndAwaitAdvance()
method to have the threads cooperatively work on the task. The arriveAndAwaitAdvance()
method will cause the thread to arrive at the Phaser and then wait for all of the other threads to arrive. Once all of the threads have arrived, the Phaser will allow the threads to proceed.
Here is a simple example that shows how to use Phaser to schedule the tasks of a four-threaded development team:
Phaser phaser = new Phaser(4);
for (int i = 0; i < 4; i++) {
final int threadId = i;
new Thread(() -> {
System.out.println("Thread " + threadId + " starting task");
phaser.arriveAndAwaitAdvance();
System.out.println("Thread " + threadId + " completing task");
}).start();
}
In the example, we first create a Phaser instance with four threads. We then create four threads and register them with the Phaser instance. Finally, we use the Phaser's arriveAndAwaitAdvance()
method to have the threads cooperatively work on the task.
When the example is run, the output will be as follows:
Thread 0 starting task
Thread 1 starting task
Thread 2 starting task
Thread 3 starting task
Thread 0 completing task
Thread 1 completing task
Thread 2 completing task
Thread 3 completing task
As you can see, the Phaser caused the threads to cooperate in the execution of the task.
In this article, we have seen how to use Java's Phaser class to schedule the tasks of a multi-threaded development team. Phaser is a powerful tool that can be used to coordinate the work of multiple threads.