Using CyclicBarrier in Java
January 16, 2023
On this page, we will learn using CyclicBarrier in our Java application.
1. The
CyclicBarrier class helps in synchronization of threads in such a way that all parties(threads) wait for each other to reach a common barrier point. This barrier is called cyclic because it can be re-used after the waiting threads are released.
2. The
CyclicBarrier is created with number of parties and with optional Runnable. All the threads of the group will wait for each other to complete and once all threads complete its task then the specified Runnable instance will execute.
3. The
CyclicBarrier is used in such programs where a party of threads of fixed size need to wait for each other.
Understanding the Working
To understand the working ofCyclicBarrier, find the diagram.
1. A group of three threads are created and started.
2. Each thread reaches to common barrier point after completing its tasks. Order of reaching to common barrier point does not matter.
3. Once each thread of the group has reached to the common barrier point,
CyclicBarrier trips and specified Runnable to the CyclicBarrier constructor, is started to execute.
Now understand by the code.
CyclicBarrierDemo.java
package com.concretepage;
import java.util.concurrent.BrokenBarrierException;
import java.util.concurrent.CyclicBarrier;
class CyclicBarrierDemo {
class Worker implements Runnable {
String workName;
CyclicBarrier barrier;
Worker(String workName, CyclicBarrier barrier) {
this.workName = workName;
this.barrier = barrier;
}
public void run() {
doWork(workName);
try {
barrier.await(); // Threads reach here after completing its task
} catch (InterruptedException e) {
e.printStackTrace();
} catch (BrokenBarrierException e) {
e.printStackTrace();
}
}
}
void doWork(String workName) {
System.out.println(workName + " processed.");
}
public static void main(String[] args) {
Runnable barrierAction = () -> System.out.println("Executing Runnable after completing all threads of the party.");
int partySize = 3;
CyclicBarrier barrier = new CyclicBarrier(partySize, barrierAction);
CyclicBarrierDemo ob = new CyclicBarrierDemo();
// Thread-1
Thread thread1 = new Thread(ob.new Worker("work-1", barrier));
// Thread-2
Thread thread2 = new Thread(ob.new Worker("work-2", barrier));
// Thread-3
Thread thread3 = new Thread(ob.new Worker("work-3", barrier));
thread1.start();
thread2.start();
thread3.start();
}
}
work-2 processed. work-3 processed. work-1 processed. Executing Runnable after completing all threads of the party.
Constructors
Find the constructors of theCyclicBarrier class.
1.
public CyclicBarrier(int parties)
CyclicBarrier that will trip when the given number of parties (threads) are waiting upon it.
Parameters:
The parties is the number of threads that must invoke
await() before the barrier is tripped.
Throws:
It throws
IllegalArgumentException, if parties is less than 1.
2.
public CyclicBarrier(int parties, Runnable barrierAction)
CyclicBarrier that will trip when the given number of parties (threads) are waiting upon it. Once the barrier is tripped, the given barrierAction is executed.
Parameters:
The parties is the number of threads that must invoke
await() before the barrier is tripped.
The barrierAction is the command to execute when the barrier is tripped, or null if there is no action.
Throws:
It throws
IllegalArgumentException, if parties is less than 1.
Methods
1.public int await() throws InterruptedException, BrokenBarrierException
Returns the arrival index of the current thread.
2.
public int await(long timeout, TimeUnit unit)
throws InterruptedException, BrokenBarrierException, TimeoutException
Returns the arrival index of the current thread.
3.
public int getNumberWaiting()
4.
public int getParties()
5.
public boolean isBroken()
6.
public void reset()
Examples
Find the example.AddMultiply.java
package com.concretepage;
import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.BrokenBarrierException;
import java.util.concurrent.CyclicBarrier;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
class AddMultiply {
static List<Integer> dataToAddList = new ArrayList<>();
class Worker implements Runnable {
int num1;
int num2;
CyclicBarrier barrier;
Worker(int num1, int num2, CyclicBarrier barrier) {
this.num1 = num1;
this.num2 = num2;
this.barrier = barrier;
}
public void run() {
int multiplyRes = addNum(num1, num2);
System.out.println(String.format("%d * %d = %d", num1, num2, multiplyRes));
dataToAddList.add(multiplyRes);
try {
barrier.await();
} catch (InterruptedException e) {
e.printStackTrace();
} catch (BrokenBarrierException e) {
e.printStackTrace();
}
}
}
int addNum(int num1, int num2) {
return num1 * num2;
}
public static void main(String[] args) {
Runnable barrierAction = () -> {
int sum = 0;
for (int i = 0; i < dataToAddList.size(); i++) {
sum += dataToAddList.get(i);
}
System.out.println("sum: " + sum);
};
int[][] arr = { { 2, 3 }, { 4, 5 }, { 6, 7 } };
final int partySize = arr.length;
CyclicBarrier barrier = new CyclicBarrier(partySize, barrierAction);
AddMultiply ob = new AddMultiply();
ExecutorService executorService = Executors.newFixedThreadPool(partySize);
for (int i = 0; i < arr.length; i++) {
executorService.execute(ob.new Worker(arr[i][0], arr[i][1], barrier));
}
executorService.shutdown();
}
}
4 * 5 = 20 2 * 3 = 6 6 * 7 = 42 sum: 68
Reusing cyclic barrier
In
CyclicBarrier, the cyclic barrier is reusable. Now find one more example. In this example, data to process are more than the number of CyclicBarrier party numbers i.e. 2 and data to process are 10. Once the 2 threads reach to the common barrier point, CyclicBarrier will trip and given Runnable starts executing. Again once two more threads reach to the common barrier point, CyclicBarrier will trip and given Runnable starts executing, and so on.
Find the example.
ReusingCyclicBarrier.java
package com.concretepage;
import java.util.concurrent.BrokenBarrierException;
import java.util.concurrent.CyclicBarrier;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
class ReusingCyclicBarrier {
class Worker implements Runnable {
int task;
CyclicBarrier barrier;
Worker(int task, CyclicBarrier barrier) {
this.task = task;
this.barrier = barrier;
}
public void run() {
System.out.println(String.format("Task %d is processed and reached to common barrier point.", task));
try {
barrier.await();
} catch (InterruptedException e) {
e.printStackTrace();
} catch (BrokenBarrierException e) {
e.printStackTrace();
}
}
}
public static void main(String[] args) {
Runnable barrierAction = () -> {
System.out.println("Barrier is tripped");
};
final int partySize = 2;
final int poolSize = 2;
CyclicBarrier barrier = new CyclicBarrier(partySize, barrierAction);
ReusingCyclicBarrier ob = new ReusingCyclicBarrier();
ExecutorService executorService = Executors.newFixedThreadPool(poolSize);
for (int i = 1; i <= 10; i++) {
executorService.execute(ob.new Worker(i, barrier));
}
executorService.shutdown();
}
}
Task 2 is processed and reached to common barrier point. Task 1 is processed and reached to common barrier point. Barrier is tripped Task 3 is processed and reached to common barrier point. Task 4 is processed and reached to common barrier point. Barrier is tripped Task 5 is processed and reached to common barrier point. Task 6 is processed and reached to common barrier point. Barrier is tripped Task 7 is processed and reached to common barrier point. Task 8 is processed and reached to common barrier point. Barrier is tripped Task 9 is processed and reached to common barrier point. Task 10 is processed and reached to common barrier point. Barrier is tripped
