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| 1 | +import java.util.concurrent.locks.ReadWriteLock; |
| 2 | +import java.util.concurrent.locks.ReentrantReadWriteLock; |
| 3 | + |
| 4 | +public class SharedState { |
| 5 | + // shared resource |
| 6 | + private volatile int data; |
| 7 | + // lock for the resource |
| 8 | + ReadWriteLock rwLock = new ReentrantReadWriteLock(); |
| 9 | + |
| 10 | + private static final int READ_CYCLES = (int)1e8; |
| 11 | + private static final int WRITE_CYCLES = (int)1e8; |
| 12 | + |
| 13 | + public SharedState(int initialData) { |
| 14 | + this.data = initialData; |
| 15 | + } |
| 16 | + |
| 17 | + /** |
| 18 | + * Retrieves the data from a private static variable. |
| 19 | + * Representing a shared resource |
| 20 | + * |
| 21 | + * @return The data value stored |
| 22 | + */ |
| 23 | + private int getData() { |
| 24 | + rwLock.readLock().lock(); |
| 25 | + try { |
| 26 | + return data; |
| 27 | + } finally { |
| 28 | + rwLock.readLock().unlock(); |
| 29 | + } |
| 30 | + } |
| 31 | + |
| 32 | + /** |
| 33 | + * Updates the value of the private static variable 'data'. |
| 34 | + */ |
| 35 | + private void updateData() { |
| 36 | + rwLock.writeLock().lock(); |
| 37 | + try { |
| 38 | + data += 1; |
| 39 | + } finally { |
| 40 | + rwLock.writeLock().unlock(); |
| 41 | + } |
| 42 | + |
| 43 | + } |
| 44 | + |
| 45 | + public static void main(String ...args) throws InterruptedException { |
| 46 | + final long startTime = System.nanoTime(); |
| 47 | + SharedState sharedState = new SharedState(0); |
| 48 | + Thread readerThread = new Thread(new Runnable() { |
| 49 | + @Override |
| 50 | + public void run() { |
| 51 | + for(int cycles = 0; cycles < READ_CYCLES; cycles++) { |
| 52 | + int value = sharedState.getData(); |
| 53 | + // to keep I/O low to influence perf |
| 54 | + if(cycles % (READ_CYCLES/10) == 0){ |
| 55 | + System.out.println("read: " + value); |
| 56 | + System.out.flush(); |
| 57 | + } |
| 58 | + } |
| 59 | + } |
| 60 | + }); |
| 61 | + Thread writerThread = new Thread(new Runnable() { |
| 62 | + @Override |
| 63 | + public void run() { |
| 64 | + for(int cycles = 0; cycles < WRITE_CYCLES; cycles++) { |
| 65 | + sharedState.updateData(); |
| 66 | + int value = sharedState.getData(); |
| 67 | + if(cycles % (WRITE_CYCLES/10) == 0){ |
| 68 | + System.out.println("post write: " + value); |
| 69 | + System.out.flush(); |
| 70 | + } |
| 71 | + } |
| 72 | + } |
| 73 | + }); |
| 74 | + readerThread.start(); |
| 75 | + writerThread.start(); |
| 76 | + readerThread.join(); |
| 77 | + writerThread.join(); |
| 78 | + final long duration = System.nanoTime() - startTime; |
| 79 | + System.out.println("time taken(ns): " + duration); |
| 80 | + } |
| 81 | +} |
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