Java Concurrency Tutorial
Selected Reading
- Concurrency - Discussion
- Concurrency - Useful Resources
- Concurrency - Quick Guide
- ConcurrentNavigableMap
- Concurrency - ConcurrentMap
- Concurrency - BlockingQueue
- Concurrency - Fork-Join framework
- Concurrency - Futures and Callables
- ScheduledThreadPoolExecutor
- Concurrency - ThreadPoolExecutor
- newSingleThreadExecutor
- newScheduledThreadPool
- Concurrency - newCachedThreadPool
- Concurrency - newFixedThreadPool
- ScheduledExecutorService
- Concurrency - ExecutorService
- Concurrency - Executor
- Concurrency - AtomicReferenceArray
- Concurrency - AtomicLongArray
- Concurrency - AtomicIntegerArray
- Concurrency - AtomicReference
- Concurrency - AtomicBoolean
- Concurrency - AtomicLong
- Concurrency - AtomicInteger
- Concurrency - Condition
- Concurrency - ReadWriteLock
- Concurrency - Lock
- Concurrency - ThreadLocalRandom
- Concurrency - ThreadLocal
- Concurrency - Deadlock
- Concurrency - Synchronization
- Interthread Communication
- Concurrency - Major Operations
- Concurrency - Environment Setup
- Concurrency - Overview
- Concurrency - Home
Selected Reading
- Who is Who
- Computer Glossary
- HR Interview Questions
- Effective Resume Writing
- Questions and Answers
- UPSC IAS Exams Notes
Concurrency - ReadWriteLock
Java Concurrency - ReadWriteLock Interface
A java.util.concurrent.locks.ReadWriteLock interface allows multiple threads to read at a time but only one thread can write at a time.
Read Lock − If no thread has locked the ReadWriteLock for writing then multiple thread can access the read lock.
Write Lock − If no thread is reading or writing, then one thread can access the write lock.
Lock Methods
Following is the pst of important methods available in the Lock class.
| Sr.No. | Method & Description |
|---|---|
| 1 | pubpc Lock readLock() Returns the lock used for reading. |
| 2 | pubpc Lock writeLock() Returns the lock used for writing. |
Example
The following TestThread program demonstrates these methods of the ReadWriteLock interface. Here we ve used readlock() to acquire the read-lock and writeLock() to acquire the write-lock.
import java.util.concurrent.locks.ReentrantReadWriteLock;
pubpc class TestThread {
private static final ReentrantReadWriteLock lock = new ReentrantReadWriteLock(true);
private static String message = "a";
pubpc static void main(String[] args) throws InterruptedException {
Thread t1 = new Thread(new WriterA());
t1.setName("Writer A");
Thread t2 = new Thread(new WriterB());
t2.setName("Writer B");
Thread t3 = new Thread(new Reader());
t3.setName("Reader");
t1.start();
t2.start();
t3.start();
t1.join();
t2.join();
t3.join();
}
static class Reader implements Runnable {
pubpc void run() {
if(lock.isWriteLocked()) {
System.out.println("Write Lock Present.");
}
lock.readLock().lock();
try {
Long duration = (long) (Math.random() * 10000);
System.out.println(Thread.currentThread().getName()
+ " Time Taken " + (duration / 1000) + " seconds.");
Thread.sleep(duration);
} catch (InterruptedException e) {
e.printStackTrace();
} finally {
System.out.println(Thread.currentThread().getName() +": "+ message );
lock.readLock().unlock();
}
}
}
static class WriterA implements Runnable {
pubpc void run() {
lock.writeLock().lock();
try {
Long duration = (long) (Math.random() * 10000);
System.out.println(Thread.currentThread().getName()
+ " Time Taken " + (duration / 1000) + " seconds.");
Thread.sleep(duration);
} catch (InterruptedException e) {
e.printStackTrace();
} finally {
message = message.concat("a");
lock.writeLock().unlock();
}
}
}
static class WriterB implements Runnable {
pubpc void run() {
lock.writeLock().lock();
try {
Long duration = (long) (Math.random() * 10000);
System.out.println(Thread.currentThread().getName()
+ " Time Taken " + (duration / 1000) + " seconds.");
Thread.sleep(duration);
} catch (InterruptedException e) {
e.printStackTrace();
} finally {
message = message.concat("b");
lock.writeLock().unlock();
}
}
}
}
This will produce the following result.
Output
Writer A Time Taken 6 seconds. Write Lock Present. Writer B Time Taken 2 seconds. Reader Time Taken 0 seconds. Reader: aabAdvertisements