Java并发编程与高并发解决方案（二）
单例模式实现线程安全
1：懒汉式
/**
* 懒汉模式 -》 双重同步锁单例模式
* 单例实例在第一次使用时进行创建
*/
@ThreadSafe
public class SingletonExample5 {
// 私有构造函数
private SingletonExample5() {
}
// 1、memory = allocate() 分配对象的内存空间
// 2、ctorInstance() 初始化对象
// 3、instance = memory 设置instance指向刚分配的内存
// JVM和cpu优化，发生了指令重排
// 1、memory = allocate() 分配对象的内存空间
// 3、instance = memory 设置instance指向刚分配的内存
// 2、ctorInstance() 初始化对象
// 单例对象 volatile + 双重检测机制 -> 禁止指令重排
private volatile static SingletonExample5 instance = null;
// 静态的工厂方法
public static SingletonExample5 getInstance() {
if (instance == null) { // 双重检测机制 // B
synchronized (SingletonExample5.class) { // 同步锁
if (instance == null) {
instance = new SingletonExample5(); // A - 3
}
}
}
return instance;
}
}2：饿汉模式
/**
* 饿汉模式
* 单例实例在类装载时进行创建
*/
@ThreadSafe
public class SingletonExample6 {
// 私有构造函数
private SingletonExample6() {
}
// 单例对象
private static SingletonExample6 instance = null;
static {
instance = new SingletonExample6();
}
// 静态的工厂方法
public static SingletonExample6 getInstance() {
return instance;
}
public static void main(String[] args) {
System.out.println(getInstance().hashCode());
System.out.println(getInstance().hashCode());
}
}3：枚举模式：最安全
/**
* 枚举模式：最安全
*/
@ThreadSafe
@Recommend
public class SingletonExample7 {
// 私有构造函数
private SingletonExample7() {
}
public static SingletonExample7 getInstance() {
return Singleton.INSTANCE.getInstance();
}
private enum Singleton {
INSTANCE;
private SingletonExample7 singleton;
// JVM保证这个方法绝对只调用一次
Singleton() {
singleton = new SingletonExample7();
}
public SingletonExample7 getInstance() {
return singleton;
}
}
}
Immutable实现线程安全
1：线程不安全的
@Slf4j
@NotThreadSafe
public class ImmutableExample1 {
private final static Integer a = 1;
private final static String b = "2";
private final static Map map = Maps.newHashMap();
static {
map.put(1, 2);
map.put(3, 4);
map.put(5, 6);
}
public static void main(String[] args) {
// a = 2;
// b = "3";
// map = Maps.newHashMap();
map.put(1, 3);
log.info("{}", map.get(1));
}
private void test(final int a) {
// a = 1;
}
} 2：线程安全的
@Slf4j
@ThreadSafe
public class ImmutableExample2 {
private static Map map = Maps.newHashMap();
static {
map.put(1, 2);
map.put(3, 4);
map.put(5, 6);
map = Collections.unmodifiableMap(map);
}
public static void main(String[] args) {
map.put(1, 3);
log.info("{}", map.get(1));
}
} 3：线程安全的
@ThreadSafe
public class ImmutableExample3 {
private final static ImmutableList list = ImmutableList.of(1, 2, 3);
private final static ImmutableSet set = ImmutableSet.copyOf(list);
private final static ImmutableMap map = ImmutableMap.of(1, 2, 3, 4);
private final static ImmutableMap map2 = ImmutableMap.builder()
.put(1, 2).put(3, 4).put(5, 6).build();
public static void main(String[] args) {
System.out.println(map2.get(3));
}
} 集合线程安全与不安全
1：ArrayList线程不安全
@Slf4j
@NotThreadSafe
public class ArrayListExample {
// 请求总数
public static int clientTotal = 5000;
// 同时并发执行的线程数
public static int threadTotal = 200;
private static List list = new ArrayList<>();
public static void main(String[] args) throws Exception {
ExecutorService executorService = Executors.newCachedThreadPool();
final Semaphore semaphore = new Semaphore(threadTotal);
final CountDownLatch countDownLatch = new CountDownLatch(clientTotal);
for (int i = 0; i < clientTotal; i++) {
final int count = i;
executorService.execute(() -> {
try {
semaphore.acquire();
update(count);
semaphore.release();
} catch (Exception e) {
log.error("exception", e);
}
countDownLatch.countDown();
});
}
countDownLatch.await();
executorService.shutdown();
log.info("size:{}", list.size());
}
private static void update(int i) {
list.add(i);
}
} 2：HashSet线程不安全
@Slf4j
@NotThreadSafe
public class HashSetExample {
// 请求总数
public static int clientTotal = 5000;
// 同时并发执行的线程数
public static int threadTotal = 200;
private static Set set = new HashSet<>();
public static void main(String[] args) throws Exception {
ExecutorService executorService = Executors.newCachedThreadPool();
final Semaphore semaphore = new Semaphore(threadTotal);
final CountDownLatch countDownLatch = new CountDownLatch(clientTotal);
for (int i = 0; i < clientTotal; i++) {
final int count = i;
executorService.execute(() -> {
try {
semaphore.acquire();
update(count);
semaphore.release();
} catch (Exception e) {
log.error("exception", e);
}
countDownLatch.countDown();
});
}
countDownLatch.await();
executorService.shutdown();
log.info("size:{}", set.size());
}
private static void update(int i) {
set.add(i);
}
} 3：HashMap线程不安全
@Slf4j
@NotThreadSafe
public class HashMapExample {
// 请求总数
public static int clientTotal = 5000;
// 同时并发执行的线程数
public static int threadTotal = 200;
private static Map map = new HashMap<>();
public static void main(String[] args) throws Exception {
ExecutorService executorService = Executors.newCachedThreadPool();
final Semaphore semaphore = new Semaphore(threadTotal);
final CountDownLatch countDownLatch = new CountDownLatch(clientTotal);
for (int i = 0; i < clientTotal; i++) {
final int count = i;
executorService.execute(() -> {
try {
semaphore.acquire();
update(count);
semaphore.release();
} catch (Exception e) {
log.error("exception", e);
}
countDownLatch.countDown();
});
}
countDownLatch.await();
executorService.shutdown();
log.info("size:{}", map.size());
}
private static void update(int i) {
map.put(i, i);
}
} 4：StringBuild线程不安全
@Slf4j
@NotThreadSafe
public class StringExample1 {
// 请求总数
public static int clientTotal = 5000;
// 同时并发执行的线程数
public static int threadTotal = 200;
public static StringBuilder stringBuilder = new StringBuilder();
public static void main(String[] args) throws Exception {
ExecutorService executorService = Executors.newCachedThreadPool();
final Semaphore semaphore = new Semaphore(threadTotal);
final CountDownLatch countDownLatch = new CountDownLatch(clientTotal);
for (int i = 0; i < clientTotal ; i++) {
executorService.execute(() -> {
try {
semaphore.acquire();
update();
semaphore.release();
} catch (Exception e) {
log.error("exception", e);
}
countDownLatch.countDown();
});
}
countDownLatch.await();
executorService.shutdown();
log.info("size:{}", stringBuilder.length());
}
private static void update() {
stringBuilder.append("1");
}
}5：StringBuffer线程安全
@Slf4j
@ThreadSafe
public class StringExample2 {
// 请求总数
public static int clientTotal = 5000;
// 同时并发执行的线程数
public static int threadTotal = 200;
public static StringBuffer stringBuffer = new StringBuffer();
public static void main(String[] args) throws Exception {
ExecutorService executorService = Executors.newCachedThreadPool();
final Semaphore semaphore = new Semaphore(threadTotal);
final CountDownLatch countDownLatch = new CountDownLatch(clientTotal);
for (int i = 0; i < clientTotal ; i++) {
executorService.execute(() -> {
try {
semaphore.acquire();
update();
semaphore.release();
} catch (Exception e) {
log.error("exception", e);
}
countDownLatch.countDown();
});
}
countDownLatch.await();
executorService.shutdown();
log.info("size:{}", stringBuffer.length());
}
private static void update() {
stringBuffer.append("1");
}
}
6：DateFormat实现线程安全
@Slf4j
@ThreadSafe
public class DateFormatExample2 {
// 请求总数
public static int clientTotal = 5000;
// 同时并发执行的线程数
public static int threadTotal = 200;
public static void main(String[] args) throws Exception {
ExecutorService executorService = Executors.newCachedThreadPool();
final Semaphore semaphore = new Semaphore(threadTotal);
final CountDownLatch countDownLatch = new CountDownLatch(clientTotal);
for (int i = 0; i < clientTotal ; i++) {
executorService.execute(() -> {
try {
semaphore.acquire();
update();
semaphore.release();
} catch (Exception e) {
log.error("exception", e);
}
countDownLatch.countDown();
});
}
countDownLatch.await();
executorService.shutdown();
}
private static void update() {
try {
SimpleDateFormat simpleDateFormat = new SimpleDateFormat("yyyyMMdd");
Date parse = simpleDateFormat.parse("20180208");
System.out.println(parse);
} catch (Exception e) {
log.error("parse exception", e);
}
}
}线程不安全
/**
线程不安全
**/
@Slf4j
@NotThreadSafe
public class DateFormatExample1 {
private static SimpleDateFormat simpleDateFormat = new SimpleDateFormat("yyyyMMdd");
// 请求总数
public static int clientTotal = 5000;
// 同时并发执行的线程数
public static int threadTotal = 200;
public static void main(String[] args) throws Exception {
ExecutorService executorService = Executors.newCachedThreadPool();
final Semaphore semaphore = new Semaphore(threadTotal);
final CountDownLatch countDownLatch = new CountDownLatch(clientTotal);
for (int i = 0; i < clientTotal ; i++) {
executorService.execute(() -> {
try {
semaphore.acquire();
update();
semaphore.release();
} catch (Exception e) {
log.error("exception", e);
}
countDownLatch.countDown();
});
}
countDownLatch.await();
executorService.shutdown();
}
private static void update() {
try {
simpleDateFormat.parse("20180208");
} catch (Exception e) {
log.error("parse exception", e);
}
}
}joda实现线程安全时间转化joda-time joda-time 2.9
@Slf4j
@ThreadSafe
public class DateFormatExample3 {
// 请求总数
public static int clientTotal = 5000;
// 同时并发执行的线程数
public static int threadTotal = 200;
private static DateTimeFormatter dateTimeFormatter = DateTimeFormat.forPattern("yyyyMMdd");
public static void main(String[] args) throws Exception {
ExecutorService executorService = Executors.newCachedThreadPool();
final Semaphore semaphore = new Semaphore(threadTotal);
final CountDownLatch countDownLatch = new CountDownLatch(clientTotal);
for (int i = 0; i < clientTotal; i++) {
final int count = i;
executorService.execute(() -> {
try {
semaphore.acquire();
update(count);
semaphore.release();
} catch (Exception e) {
log.error("exception", e);
}
countDownLatch.countDown();
});
}
countDownLatch.await();
executorService.shutdown();
}
private static void update(int i) {
log.info("{}, {}", i, DateTime.parse("20180208", dateTimeFormatter).toDate());
}
}
Vector的使用
// java.util.ConcurrentModificationException
private static void test1(Vector v1) { // foreach
for(Integer i : v1) {
if (i.equals(3)) {
v1.remove(i);
}
}
}
// java.util.ConcurrentModificationException
private static void test2(Vector v1) { // iterator
Iterator iterator = v1.iterator();
while (iterator.hasNext()) {
Integer i = iterator.next();
if (i.equals(3)) {
v1.remove(i);
}
}
}
// success
private static void test3(Vector v1) { // for
for (int i = 0; i < v1.size(); i++) {
if (v1.get(i).equals(3)) {
v1.remove(i);
}
}
}
public static void main(String[] args) {
Vector vector = new Vector<>();
vector.add(1);
vector.add(2);
vector.add(3);
test1(vector);
}