Java Semaphore

java.util.concurrent.Semaphore

A counting semaphore. The methods acquire() and release() are used here instead of P() and V(). Each acquire() blocks if necessary until a permit is available, and then takes it. Each release() adds a permit, potentially releasing a blocking acquirer. [1]

+ Show Code

[[code type="Java"]]
import java.util.concurrent.Semaphore;
import java.util.Random;

//Solving the mutual exclusion problem using Semaphore class

class Process2 extends Thread
{
private static final Random rand = new Random();

private int id;

private Semaphore sem;

public Process2(int i, Semaphore s)
{
id = i;
sem = s;
}

private void busy()
{
try
{
sleep(rand.nextInt(500));
}
catch (InterruptedException e)
{
}
}

private void noncritical()
{
System.out.println("Thread " + id + " is NON critical");
busy();
}

private void critical()
{
System.out.println("Thread " + id + " entering critical section");
busy();
System.out.println("Thread " + id + " leaving critical section");
}

public void run()
{
for (int i = 0; i < 2; ++i)
{
noncritical();
try
{
sem.acquire();
} catch (InterruptedException e)
{
// …
}
critical();
sem.release();
}
}

public static void main(String[] args)
{
final int N = 4;

System.out.println("Busy waiting…");

//Semaphore(int permits, boolean fair)
Semaphore sem = new Semaphore(N, true);

Process2[] p = new Process2[N];

for (int i = 0; i < N; i++)
{
p[i] = new Process2(i, sem);
p[i].start();
}
}
}

[[/code]]

Need More Help?

Bibliography

1. Java API

More Examples on Java

java

Poll

Special Discounts for Students