import java.util.concurrent.Semaphore;
public class BoundedBuffer<E> {
private final Semaphore availableItems, availableSpaces;
private final E[] items;
private int putPosition = 0;
private int takePosition = 0;
@SuppressWarnings("unchecked")
public BoundedBuffer(int capacity) {
availableItems = new Semaphore(0);
availableSpaces = new Semaphore(capacity);
items = (E[]) new Object[capacity];
}
public boolean isEmpty() {
return availableItems.availablePermits() == 0;
}
public boolean isFull() {
return availableSpaces.availablePermits() == 0;
}
public void put(E x) throws InterruptedException {
availableSpaces.acquire();
doInsert(x);
availableItems.release();
}
public E take() throws InterruptedException {
availableItems.acquire();
E item = doExtract();
availableSpaces.release();
return item;
}
private synchronized void doInsert(E x) {
int i = putPosition;
items[i] = x;
putPosition = (++i == items.length)? 0 : i;
}
private synchronized E doExtract() {
int i = takePosition;
E x = items[i];
items[i] = null;
takePosition = (++i == items.length)?
0 : i;
return x;
}
}
import static org.junit.Assert.*;
import org.junit.Test;
public class BoundedBufferTests {
@Test
public void testIsEmptyWhenConstructed() {
BoundedBuffer<Integer> bb = new BoundedBuffer<Integer>(10);
assertTrue(bb.isEmpty());
assertFalse(bb.isFull());
}
@Test
public void testIsFullAfterPuts() throws InterruptedException {
BoundedBuffer<Integer> bb = new BoundedBuffer<Integer>(10);
for (int i = 0; i < 10; i++) {
bb.put(i);
}
assertTrue(bb.isFull());
assertTrue(bb.isEmpty());
}
} @Test
public void testTakeBlocksWhenEmpty(){
final BoundedBuffer<Integer> bb = new BoundedBuffer<Integer>(10);
Thread taker = new Thread(){
@Override
public void run() {
try {
int unused = bb.take();
fail(); //假设运行到这里。那么表示出现了一个错误
} catch (InterruptedException e) { }
}
};
try {
taker.start();
Thread.sleep(LOCKUP_DETECT_TIMEOUT);
taker.interrupt();
taker.join(LOCKUP_DETECT_TIMEOUT);
assertFalse(taker.isAlive());
} catch (InterruptedException e) {
fail();
}
}被堵塞线程并不须要进入WAITING或者TIMED_WAITING等状态，因此JVM能够选择通过自旋等待来实现堵塞。
import java.util.concurrent.CyclicBarrier;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.atomic.AtomicInteger;
import junit.framework.TestCase;
public class PutTakeTest extends TestCase {
private static final ExecutorService pool = Executors.newCachedThreadPool();
private final AtomicInteger putSum = new AtomicInteger(0);
private final AtomicInteger takeSum = new AtomicInteger(0);
private final CyclicBarrier barrier;
private final BoundedBuffer<Integer> bb;
private final int nTrials, nPairs;
public static void main(String[] args) {
new PutTakeTest(10, 10, 100000).test(); // 演示样例參数
pool.shutdown();
}
static int xorShift(int y) {
y ^= (y << 6);
y ^= (y >>> 21);
y ^= (y << 7);
return y;
}
public PutTakeTest(int capacity, int nPairs, int nTrials) {
this.bb = new BoundedBuffer<Integer>(capacity);
this.nTrials = nTrials;
this.nPairs = nPairs;
this.barrier = new CyclicBarrier(nPairs * 2 + 1);
}
void test() {
try {
for (int i = 0; i < nPairs; i++) {
pool.execute(new Producer());
pool.execute(new Consumer());
}
barrier.await(); // 等待全部的线程就绪
barrier.await(); // 等待全部的线程运行完毕
assertEquals(putSum.get(), takeSum.get());
} catch (Exception e) {
throw new RuntimeException(e);
}
}
class Producer implements Runnable {
@Override
public void run() {
try {
int seed = (this.hashCode() ^ (int) System.nanoTime());
int sum = 0;
barrier.await();
for (int i = nTrials; i > 0; --i) {
bb.put(seed);
sum += seed;
seed = xorShift(seed);
}
putSum.getAndAdd(sum);
barrier.await();
} catch (Exception e) {
throw new RuntimeException(e);
}
}
}
class Consumer implements Runnable {
@Override
public void run() {
try {
barrier.await();
int sum = 0;
for (int i = nTrials; i > 0; --i) {
sum += bb.take();
}
takeSum.getAndAdd(sum);
barrier.await();
} catch (Exception e) {
throw new RuntimeException(e);
}
}
}
}class Big {
double[] data = new double[100000];
};
void testLeak() throws InterruptedException{
BoundedBuffer<Big> bb = new BoundedBuffer<Big>(CAPACITY);
int heapSize1 = /* 生成堆的快照 */;
for (int i = 0; i < CAPACITY; i++){
bb.put(new Big());
}
for (int i = 0; i < CAPACITY; i++){
bb.take();
}
int heapSize2 = /* 生成堆的快照 */;
assertTrue(Math.abs(heapSize1 - heapSize2) < THRESHOLD);
} this .timer = new BarrierTimer();
this .barrier = new CyclicBarrier(nPairs * 2 + 1, timer);
public class BarrierTimer implements Runnable{
private boolean started ;
private long startTime ;
private long endTime ;
@Override
public synchronized void run() {
long t = System.nanoTime();
if (!started ){
started = true ;
startTime = t;
} else {
endTime = t;
}
}
public synchronized void clear(){
started = false ;
}
public synchronized long getTime(){
return endTime - startTime;
}
} void test(){
try {
timer.clear();
for (int i = 0; i < nPairs; i++){
pool .execute( new Producer());
pool .execute( new Consumer());
}
barrier .await();
barrier .await();
long nsPerItem = timer.getTime() / ( nPairs * (long )nTrials );
System. out .println("Throughput: " + nsPerItem + " ns/item");
assertEquals(putSum.get(), takeSum.get() )
} catch (Exception e) {
throw new RuntimeException(e);
}
} public static void main(String[] args) throws InterruptedException {
int tpt = 100000; // 每一个线程中的測试次数
for (int cap = 1; cap <= tpt; cap *= 10){
System. out .println("Capacity: " + cap);
for (int pairs = 1; pairs <= 128; pairs *= 2){
TimedPutTakeTest t = new TimedPutTakeTest(cap, pairs, tpt);
System. out .println("Pairs: " + pairs + "\t");
t.test();
System. out .println("\t" );
Thread. sleep(1000);
t.test();
System. out .println();
Thread. sleep(1000);
}
}
pool .shutdown();
}版权声明：本文博主原创文章，博客，未经同意不得转载。
原文：http://www.cnblogs.com/gcczhongduan/p/4850070.html